from sympy import (acos, acosh, asinh, atan, cos, Derivative, diff, dsolve, Dummy, Eq, Ne, erf, erfi, exp, Function, I, Integral, LambertW, log, O, pi, Rational, rootof, S, simplify, sin, sqrt, Subs, Symbol, tan, asin, sinh, Piecewise, symbols, Poly, sec, Ei, re, im) from sympy.solvers.ode import (_undetermined_coefficients_match, checkodesol, classify_ode, classify_sysode, constant_renumber, constantsimp, homogeneous_order, infinitesimals, checkinfsol, checksysodesol, solve_ics, dsolve, get_numbered_constants) from sympy.solvers.deutils import ode_order from sympy.utilities.pytest import XFAIL, skip, raises, slow, ON_TRAVIS C0, C1, C2, C3, C4, C5, C6, C7, C8, C9, C10 = symbols('C0:11') u, x, y, z = symbols('u,x:z', real=True) f = Function('f') g = Function('g') h = Function('h') # Note: the tests below may fail (but still be correct) if ODE solver, # the integral engine, solve(), or even simplify() changes. Also, in # differently formatted solutions, the arbitrary constants might not be # equal. Using specific hints in tests can help to avoid this. # Tests of order higher than 1 should run the solutions through # constant_renumber because it will normalize it (constant_renumber causes # dsolve() to return different results on different machines) def test_linear_2eq_order1(): x, y, z = symbols('x, y, z', cls=Function) k, l, m, n = symbols('k, l, m, n', Integer=True) t = Symbol('t') x0, y0 = symbols('x0, y0', cls=Function) eq1 = (Eq(diff(x(t),t), 9*y(t)), Eq(diff(y(t),t), 12*x(t))) sol1 = [Eq(x(t), 9*C1*exp(6*sqrt(3)*t) + 9*C2*exp(-6*sqrt(3)*t)), \ Eq(y(t), 6*sqrt(3)*C1*exp(6*sqrt(3)*t) - 6*sqrt(3)*C2*exp(-6*sqrt(3)*t))] assert checksysodesol(eq1, sol1) == (True, [0, 0]) eq2 = (Eq(diff(x(t),t), 2*x(t) + 4*y(t)), Eq(diff(y(t),t), 12*x(t) + 41*y(t))) sol2 = [Eq(x(t), 4*C1*exp(t*(sqrt(1713)/2 + S(43)/2)) + 4*C2*exp(t*(-sqrt(1713)/2 + S(43)/2))), \ Eq(y(t), C1*(S(39)/2 + sqrt(1713)/2)*exp(t*(sqrt(1713)/2 + S(43)/2)) + \ C2*(-sqrt(1713)/2 + S(39)/2)*exp(t*(-sqrt(1713)/2 + S(43)/2)))] assert checksysodesol(eq2, sol2) == (True, [0, 0]) eq3 = (Eq(diff(x(t),t), x(t) + y(t)), Eq(diff(y(t),t), -2*x(t) + 2*y(t))) sol3 = [Eq(x(t), (C1*cos(sqrt(7)*t/2) + C2*sin(sqrt(7)*t/2))*exp(3*t/2)), \ Eq(y(t), (C1*(-sqrt(7)*sin(sqrt(7)*t/2)/2 + cos(sqrt(7)*t/2)/2) + \ C2*(sin(sqrt(7)*t/2)/2 + sqrt(7)*cos(sqrt(7)*t/2)/2))*exp(3*t/2))] assert checksysodesol(eq3, sol3) == (True, [0, 0]) eq4 = (Eq(diff(x(t),t), x(t) + y(t) + 9), Eq(diff(y(t),t), 2*x(t) + 5*y(t) + 23)) sol4 = [Eq(x(t), C1*exp(t*(sqrt(6) + 3)) + C2*exp(t*(-sqrt(6) + 3)) - S(22)/3), \ Eq(y(t), C1*(2 + sqrt(6))*exp(t*(sqrt(6) + 3)) + C2*(-sqrt(6) + 2)*exp(t*(-sqrt(6) + 3)) - S(5)/3)] assert checksysodesol(eq4, sol4) == (True, [0, 0]) eq5 = (Eq(diff(x(t),t), x(t) + y(t) + 81), Eq(diff(y(t),t), -2*x(t) + y(t) + 23)) sol5 = [Eq(x(t), (C1*cos(sqrt(2)*t) + C2*sin(sqrt(2)*t))*exp(t) - S(58)/3), \ Eq(y(t), (-sqrt(2)*C1*sin(sqrt(2)*t) + sqrt(2)*C2*cos(sqrt(2)*t))*exp(t) - S(185)/3)] assert checksysodesol(eq5, sol5) == (True, [0, 0]) eq6 = (Eq(diff(x(t),t), 5*t*x(t) + 2*y(t)), Eq(diff(y(t),t), 2*x(t) + 5*t*y(t))) sol6 = [Eq(x(t), (C1*exp(2*t) + C2*exp(-2*t))*exp(S(5)/2*t**2)), \ Eq(y(t), (C1*exp(2*t) - C2*exp(-2*t))*exp(S(5)/2*t**2))] s = dsolve(eq6) assert checksysodesol(eq6, sol6) == (True, [0, 0]) eq7 = (Eq(diff(x(t),t), 5*t*x(t) + t**2*y(t)), Eq(diff(y(t),t), -t**2*x(t) + 5*t*y(t))) sol7 = [Eq(x(t), (C1*cos((t**3)/3) + C2*sin((t**3)/3))*exp(S(5)/2*t**2)), \ Eq(y(t), (-C1*sin((t**3)/3) + C2*cos((t**3)/3))*exp(S(5)/2*t**2))] assert checksysodesol(eq7, sol7) == (True, [0, 0]) eq8 = (Eq(diff(x(t),t), 5*t*x(t) + t**2*y(t)), Eq(diff(y(t),t), -t**2*x(t) + (5*t+9*t**2)*y(t))) sol8 = [Eq(x(t), (C1*exp((sqrt(77)/2 + S(9)/2)*(t**3)/3) + \ C2*exp((-sqrt(77)/2 + S(9)/2)*(t**3)/3))*exp(S(5)/2*t**2)), \ Eq(y(t), (C1*(sqrt(77)/2 + S(9)/2)*exp((sqrt(77)/2 + S(9)/2)*(t**3)/3) + \ C2*(-sqrt(77)/2 + S(9)/2)*exp((-sqrt(77)/2 + S(9)/2)*(t**3)/3))*exp(S(5)/2*t**2))] assert checksysodesol(eq8, sol8) == (True, [0, 0]) eq10 = (Eq(diff(x(t),t), 5*t*x(t) + t**2*y(t)), Eq(diff(y(t),t), (1-t**2)*x(t) + (5*t+9*t**2)*y(t))) sol10 = [Eq(x(t), C1*x0(t) + C2*x0(t)*Integral(t**2*exp(Integral(5*t, t))*exp(Integral(9*t**2 + 5*t, t))/x0(t)**2, t)), \ Eq(y(t), C1*y0(t) + C2*(y0(t)*Integral(t**2*exp(Integral(5*t, t))*exp(Integral(9*t**2 + 5*t, t))/x0(t)**2, t) + \ exp(Integral(5*t, t))*exp(Integral(9*t**2 + 5*t, t))/x0(t)))] s = dsolve(eq10) assert s == sol10 # too complicated to test with subs and simplify # assert checksysodesol(eq10, sol10) == (True, [0, 0]) # this one fails def test_linear_2eq_order1_nonhomog_linear(): e = [Eq(diff(f(x), x), f(x) + g(x) + 5*x), Eq(diff(g(x), x), f(x) - g(x))] raises(NotImplementedError, lambda: dsolve(e)) def test_linear_2eq_order1_nonhomog(): # Note: once implemented, add some tests esp. with resonance e = [Eq(diff(f(x), x), f(x) + exp(x)), Eq(diff(g(x), x), f(x) + g(x) + x*exp(x))] raises(NotImplementedError, lambda: dsolve(e)) def test_linear_2eq_order1_type2_degen(): e = [Eq(diff(f(x), x), f(x) + 5), Eq(diff(g(x), x), f(x) + 7)] s1 = [Eq(f(x), C1*exp(x) - 5), Eq(g(x), C1*exp(x) - C2 + 2*x - 5)] assert checksysodesol(e, s1) == (True, [0, 0]) def test_dsolve_linear_2eq_order1_diag_triangular(): e = [Eq(diff(f(x), x), f(x)), Eq(diff(g(x), x), g(x))] s1 = [Eq(f(x), C1*exp(x)), Eq(g(x), C2*exp(x))] assert checksysodesol(e, s1) == (True, [0, 0]) e = [Eq(diff(f(x), x), 2*f(x)), Eq(diff(g(x), x), 3*f(x) + 7*g(x))] s1 = [Eq(f(x), -5*C2*exp(2*x)), Eq(g(x), 5*C1*exp(7*x) + 3*C2*exp(2*x))] assert checksysodesol(e, s1) == (True, [0, 0]) def test_sysode_linear_2eq_order1_type1_D_lt_0(): e = [Eq(diff(f(x), x), -9*I*f(x) - 4*g(x)), Eq(diff(g(x), x), -4*I*g(x))] s1 = [Eq(f(x), -4*C1*exp(-4*I*x) - 4*C2*exp(-9*I*x)), \ Eq(g(x), 5*I*C1*exp(-4*I*x))] assert checksysodesol(e, s1) == (True, [0, 0]) def test_sysode_linear_2eq_order1_type1_D_lt_0_b_eq_0(): e = [Eq(diff(f(x), x), -9*I*f(x)), Eq(diff(g(x), x), -4*I*g(x))] s1 = [Eq(f(x), -5*I*C2*exp(-9*I*x)), Eq(g(x), 5*I*C1*exp(-4*I*x))] assert checksysodesol(e, s1) == (True, [0, 0]) def test_sysode_linear_2eq_order1_many_zeros(): t = Symbol('t') corner_cases = [(0, 0, 0, 0), (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1), (1, 0, 0, I), (I, 0, 0, -I), (0, I, 0, 0), (0, I, I, 0)] s1 = [[Eq(f(t), C1), Eq(g(t), C2)], [Eq(f(t), C1*exp(t)), Eq(g(t), -C2)], [Eq(f(t), C1 + C2*t), Eq(g(t), C2)], [Eq(f(t), C2), Eq(g(t), C1 + C2*t)], [Eq(f(t), -C2), Eq(g(t), C1*exp(t))], [Eq(f(t), C1*(1 - I)*exp(t)), Eq(g(t), C2*(-1 + I)*exp(I*t))], [Eq(f(t), 2*I*C1*exp(I*t)), Eq(g(t), -2*I*C2*exp(-I*t))], [Eq(f(t), I*C1 + I*C2*t), Eq(g(t), C2)], [Eq(f(t), I*C1*exp(I*t) + I*C2*exp(-I*t)), \ Eq(g(t), I*C1*exp(I*t) - I*C2*exp(-I*t))] ] for r, sol in zip(corner_cases, s1): eq = [Eq(diff(f(t), t), r[0]*f(t) + r[1]*g(t)), Eq(diff(g(t), t), r[2]*f(t) + r[3]*g(t))] assert checksysodesol(eq, sol) == (True, [0, 0]) def test_dsolve_linsystem_symbol_piecewise(): u = Symbol('u') # XXX it's more complicated with real u eq = (Eq(diff(f(x), x), 2*f(x) + g(x)), Eq(diff(g(x), x), u*f(x))) s1 = [Eq(f(x), Piecewise((C1*exp(x*(sqrt(4*u + 4)/2 + 1)) + C2*exp(x*(-sqrt(4*u + 4)/2 + 1)), Ne(4*u + 4, 0)), ((C1 + C2*(x + Piecewise((0, Eq(sqrt(4*u + 4)/2 + 1, 2)), (1/(-sqrt(4*u + 4)/2 + 1), True))))*exp(x*(sqrt(4*u + 4)/2 + 1)), True))), Eq(g(x), Piecewise((C1*(sqrt(4*u + 4)/2 - 1)*exp(x*(sqrt(4*u + 4)/2 + 1)) + C2*(-sqrt(4*u + 4)/2 - 1)*exp(x*(-sqrt(4*u + 4)/2 + 1)), Ne(4*u + 4, 0)), ((C1*(sqrt(4*u + 4)/2 - 1) + C2*(x*(sqrt(4*u + 4)/2 - 1) + Piecewise((1, Eq(sqrt(4*u + 4)/2 + 1, 2)), (0, True))))*exp(x*(sqrt(4*u + 4)/2 + 1)), True)))] assert dsolve(eq) == s1 # FIXME: assert checksysodesol(eq, s) == (True, [0, 0]) # Remove lines below when checksysodesol works s = [(l.lhs, l.rhs) for l in s1] for v in [0, 7, -42, 5*I, 3 + 4*I]: assert eq[0].subs(s).subs(u, v).doit().simplify() assert eq[1].subs(s).subs(u, v).doit().simplify() # example from https://groups.google.com/d/msg/sympy/xmzoqW6tWaE/sf0bgQrlCgAJ i, r1, c1, r2, c2, t = symbols('i, r1, c1, r2, c2, t') x1 = Function('x1') x2 = Function('x2') eq1 = r1*c1*Derivative(x1(t), t) + x1(t) - x2(t) - r1*i eq2 = r2*c1*Derivative(x1(t), t) + r2*c2*Derivative(x2(t), t) + x2(t) - r2*i sol = dsolve((eq1, eq2)) # FIXME: assert checksysodesol(eq, sol) == (True, [0, 0]) # Remove line below when checksysodesol works assert all(s.has(Piecewise) for s in sol) @slow def test_linear_2eq_order2(): x, y, z = symbols('x, y, z', cls=Function) k, l, m, n = symbols('k, l, m, n', Integer=True) t, l = symbols('t, l') x0, y0 = symbols('x0, y0', cls=Function) eq1 = (Eq(diff(x(t),t,t), 5*x(t) + 43*y(t)), Eq(diff(y(t),t,t), x(t) + 9*y(t))) sol1 = [Eq(x(t), 43*C1*exp(t*rootof(l**4 - 14*l**2 + 2, 0)) + 43*C2*exp(t*rootof(l**4 - 14*l**2 + 2, 1)) + \ 43*C3*exp(t*rootof(l**4 - 14*l**2 + 2, 2)) + 43*C4*exp(t*rootof(l**4 - 14*l**2 + 2, 3))), \ Eq(y(t), C1*(rootof(l**4 - 14*l**2 + 2, 0)**2 - 5)*exp(t*rootof(l**4 - 14*l**2 + 2, 0)) + \ C2*(rootof(l**4 - 14*l**2 + 2, 1)**2 - 5)*exp(t*rootof(l**4 - 14*l**2 + 2, 1)) + \ C3*(rootof(l**4 - 14*l**2 + 2, 2)**2 - 5)*exp(t*rootof(l**4 - 14*l**2 + 2, 2)) + \ C4*(rootof(l**4 - 14*l**2 + 2, 3)**2 - 5)*exp(t*rootof(l**4 - 14*l**2 + 2, 3)))] assert dsolve(eq1) == sol1 # FIXME: assert checksysodesol(eq1, sol1) == (True, [0, 0]) # this one fails eq2 = (Eq(diff(x(t),t,t), 8*x(t)+3*y(t)+31), Eq(diff(y(t),t,t), 9*x(t)+7*y(t)+12)) sol2 = [Eq(x(t), 3*C1*exp(t*rootof(l**4 - 15*l**2 + 29, 0)) + 3*C2*exp(t*rootof(l**4 - 15*l**2 + 29, 1)) + \ 3*C3*exp(t*rootof(l**4 - 15*l**2 + 29, 2)) + 3*C4*exp(t*rootof(l**4 - 15*l**2 + 29, 3)) - S(181)/29), \ Eq(y(t), C1*(rootof(l**4 - 15*l**2 + 29, 0)**2 - 8)*exp(t*rootof(l**4 - 15*l**2 + 29, 0)) + \ C2*(rootof(l**4 - 15*l**2 + 29, 1)**2 - 8)*exp(t*rootof(l**4 - 15*l**2 + 29, 1)) + \ C3*(rootof(l**4 - 15*l**2 + 29, 2)**2 - 8)*exp(t*rootof(l**4 - 15*l**2 + 29, 2)) + \ C4*(rootof(l**4 - 15*l**2 + 29, 3)**2 - 8)*exp(t*rootof(l**4 - 15*l**2 + 29, 3)) + S(183)/29)] assert dsolve(eq2) == sol2 # FIXME: assert checksysodesol(eq2, sol2) == (True, [0, 0]) # this one fails eq3 = (Eq(diff(x(t),t,t) - 9*diff(y(t),t) + 7*x(t),0), Eq(diff(y(t),t,t) + 9*diff(x(t),t) + 7*y(t),0)) sol3 = [Eq(x(t), C1*cos(t*(S(9)/2 + sqrt(109)/2)) + C2*sin(t*(S(9)/2 + sqrt(109)/2)) + C3*cos(t*(-sqrt(109)/2 + S(9)/2)) + \ C4*sin(t*(-sqrt(109)/2 + S(9)/2))), Eq(y(t), -C1*sin(t*(S(9)/2 + sqrt(109)/2)) + C2*cos(t*(S(9)/2 + sqrt(109)/2)) - \ C3*sin(t*(-sqrt(109)/2 + S(9)/2)) + C4*cos(t*(-sqrt(109)/2 + S(9)/2)))] assert dsolve(eq3) == sol3 assert checksysodesol(eq3, sol3) == (True, [0, 0]) eq4 = (Eq(diff(x(t),t,t), 9*t*diff(y(t),t)-9*y(t)), Eq(diff(y(t),t,t),7*t*diff(x(t),t)-7*x(t))) sol4 = [Eq(x(t), C3*t + t*Integral((9*C1*exp(3*sqrt(7)*t**2/2) + 9*C2*exp(-3*sqrt(7)*t**2/2))/t**2, t)), \ Eq(y(t), C4*t + t*Integral((3*sqrt(7)*C1*exp(3*sqrt(7)*t**2/2) - 3*sqrt(7)*C2*exp(-3*sqrt(7)*t**2/2))/t**2, t))] assert dsolve(eq4) == sol4 assert checksysodesol(eq4, sol4) == (True, [0, 0]) eq5 = (Eq(diff(x(t),t,t), (log(t)+t**2)*diff(x(t),t)+(log(t)+t**2)*3*diff(y(t),t)), Eq(diff(y(t),t,t), \ (log(t)+t**2)*2*diff(x(t),t)+(log(t)+t**2)*9*diff(y(t),t))) sol5 = [Eq(x(t), -sqrt(22)*(C1*Integral(exp((-sqrt(22) + 5)*Integral(t**2 + log(t), t)), t) + C2 - \ C3*Integral(exp((sqrt(22) + 5)*Integral(t**2 + log(t), t)), t) - C4 - \ (sqrt(22) + 5)*(C1*Integral(exp((-sqrt(22) + 5)*Integral(t**2 + log(t), t)), t) + C2) + \ (-sqrt(22) + 5)*(C3*Integral(exp((sqrt(22) + 5)*Integral(t**2 + log(t), t)), t) + C4))/88), \ Eq(y(t), -sqrt(22)*(C1*Integral(exp((-sqrt(22) + 5)*Integral(t**2 + log(t), t)), t) + \ C2 - C3*Integral(exp((sqrt(22) + 5)*Integral(t**2 + log(t), t)), t) - C4)/44)] assert dsolve(eq5) == sol5 assert checksysodesol(eq5, sol5) == (True, [0, 0]) eq6 = (Eq(diff(x(t),t,t), log(t)*t*diff(y(t),t) - log(t)*y(t)), Eq(diff(y(t),t,t), log(t)*t*diff(x(t),t) - log(t)*x(t))) sol6 = [Eq(x(t), C3*t + t*Integral((C1*exp(Integral(t*log(t), t)) + \ C2*exp(-Integral(t*log(t), t)))/t**2, t)), Eq(y(t), C4*t + t*Integral((C1*exp(Integral(t*log(t), t)) - \ C2*exp(-Integral(t*log(t), t)))/t**2, t))] assert dsolve(eq6) == sol6 assert checksysodesol(eq6, sol6) == (True, [0, 0]) eq7 = (Eq(diff(x(t),t,t), log(t)*(t*diff(x(t),t) - x(t)) + exp(t)*(t*diff(y(t),t) - y(t))), \ Eq(diff(y(t),t,t), (t**2)*(t*diff(x(t),t) - x(t)) + (t)*(t*diff(y(t),t) - y(t)))) sol7 = [Eq(x(t), C3*t + t*Integral((C1*x0(t) + C2*x0(t)*Integral(t*exp(t)*exp(Integral(t**2, t))*\ exp(Integral(t*log(t), t))/x0(t)**2, t))/t**2, t)), Eq(y(t), C4*t + t*Integral((C1*y0(t) + \ C2*(y0(t)*Integral(t*exp(t)*exp(Integral(t**2, t))*exp(Integral(t*log(t), t))/x0(t)**2, t) + \ exp(Integral(t**2, t))*exp(Integral(t*log(t), t))/x0(t)))/t**2, t))] assert dsolve(eq7) == sol7 # FIXME: assert checksysodesol(eq7, sol7) == (True, [0, 0]) eq8 = (Eq(diff(x(t),t,t), t*(4*x(t) + 9*y(t))), Eq(diff(y(t),t,t), t*(12*x(t) - 6*y(t)))) sol8 = ("[Eq(x(t), -sqrt(133)*((-sqrt(133) - 1)*(C2*(133*t**8/24 - t**3/6 + sqrt(133)*t**3/2 + 1) + " "C1*t*(sqrt(133)*t**4/6 - t**3/12 + 1) + O(t**6)) - (-1 + sqrt(133))*(C2*(-sqrt(133)*t**3/6 - t**3/6 + 1) + " "C1*t*(-sqrt(133)*t**3/12 - t**3/12 + 1) + O(t**6)) - 4*C2*(133*t**8/24 - t**3/6 + sqrt(133)*t**3/2 + 1) + " "4*C2*(-sqrt(133)*t**3/6 - t**3/6 + 1) - 4*C1*t*(sqrt(133)*t**4/6 - t**3/12 + 1) + " "4*C1*t*(-sqrt(133)*t**3/12 - t**3/12 + 1) + O(t**6))/3192), Eq(y(t), -sqrt(133)*(-C2*(133*t**8/24 - t**3/6 + " "sqrt(133)*t**3/2 + 1) + C2*(-sqrt(133)*t**3/6 - t**3/6 + 1) - C1*t*(sqrt(133)*t**4/6 - t**3/12 + 1) + " "C1*t*(-sqrt(133)*t**3/12 - t**3/12 + 1) + O(t**6))/266)]") assert str(dsolve(eq8)) == sol8 # FIXME: assert checksysodesol(eq8, sol8) == (True, [0, 0]) eq9 = (Eq(diff(x(t),t,t), t*(4*diff(x(t),t) + 9*diff(y(t),t))), Eq(diff(y(t),t,t), t*(12*diff(x(t),t) - 6*diff(y(t),t)))) sol9 = [Eq(x(t), -sqrt(133)*(4*C1*Integral(exp((-sqrt(133) - 1)*Integral(t, t)), t) + 4*C2 - \ 4*C3*Integral(exp((-1 + sqrt(133))*Integral(t, t)), t) - 4*C4 - (-1 + sqrt(133))*(C1*Integral(exp((-sqrt(133) - \ 1)*Integral(t, t)), t) + C2) + (-sqrt(133) - 1)*(C3*Integral(exp((-1 + sqrt(133))*Integral(t, t)), t) + \ C4))/3192), Eq(y(t), -sqrt(133)*(C1*Integral(exp((-sqrt(133) - 1)*Integral(t, t)), t) + C2 - \ C3*Integral(exp((-1 + sqrt(133))*Integral(t, t)), t) - C4)/266)] assert dsolve(eq9) == sol9 assert checksysodesol(eq9, sol9) == (True, [0, 0]) eq10 = (t**2*diff(x(t),t,t) + 3*t*diff(x(t),t) + 4*t*diff(y(t),t) + 12*x(t) + 9*y(t), \ t**2*diff(y(t),t,t) + 2*t*diff(x(t),t) - 5*t*diff(y(t),t) + 15*x(t) + 8*y(t)) sol10 = [Eq(x(t), -C1*(-2*sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 13 + 2*sqrt(-284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + \ 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) - 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + \ 346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3))))*exp((-sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + \ 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3))/2 + 1 + sqrt(-284/sqrt(-346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) - 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)))/2)*log(t)) - \ C2*(-2*sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + \ 13 - 2*sqrt(-284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) - 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3))))*exp((-sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + \ 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3))/2 + 1 - sqrt(-284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + \ 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) - 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)))/2)*log(t)) - C3*t**(1 + sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + \ 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3))/2 + sqrt(-2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)))/2)*(2*sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 13 + 2*sqrt(-2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)))) - C4*t**(-sqrt(-2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)))/2 + 1 + sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3))/2)*(-2*sqrt(-2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3))) + 2*sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 13)), Eq(y(t), C1*(-sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + \ 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 14 + (-sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + \ 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3))/2 + 1 + sqrt(-284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + \ 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) - 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)))/2)**2 + sqrt(-284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + \ 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) - 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3))))*exp((-sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3))/2 + 1 + sqrt(-284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + \ 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) - 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)))/2)*log(t)) + C2*(-sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + \ 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 14 - sqrt(-284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + \ 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) - 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3))) + (-sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3))/2 + 1 - sqrt(-284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + \ 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) - 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)))/2)**2)*exp((-sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3))/2 + 1 - sqrt(-284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + \ 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) - 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)))/2)*log(t)) + C3*t**(1 + sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + \ 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3))/2 + sqrt(-2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)))/2)*(sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + sqrt(-2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3))) + 14 + (1 + sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3))/2 + sqrt(-2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + 346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)))/2)**2) + C4*t**(-sqrt(-2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + \ 346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + \ 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)))/2 + 1 + sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + \ 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3))/2)*(-sqrt(-2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + \ 8 + 346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + \ 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3))) + (-sqrt(-2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3) + 8 + \ 346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 284/sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + \ 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)))/2 + 1 + sqrt(-346/(3*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + \ 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3))/2)**2 + sqrt(-346/(3*(S(4333)/4 + \ 5*sqrt(70771857)/36)**(S(1)/3)) + 4 + 2*(S(4333)/4 + 5*sqrt(70771857)/36)**(S(1)/3)) + 14))] assert dsolve(eq10) == sol10 # FIXME: assert checksysodesol(eq10, sol10) == (True, [0, 0]) # this hangs or at least takes a while... def test_linear_3eq_order1(): x, y, z = symbols('x, y, z', cls=Function) t = Symbol('t') eq1 = (Eq(diff(x(t),t), 21*x(t)), Eq(diff(y(t),t), 17*x(t)+3*y(t)), Eq(diff(z(t),t), 5*x(t)+7*y(t)+9*z(t))) sol1 = [Eq(x(t), C1*exp(21*t)), Eq(y(t), 17*C1*exp(21*t)/18 + C2*exp(3*t)), \ Eq(z(t), 209*C1*exp(21*t)/216 - 7*C2*exp(3*t)/6 + C3*exp(9*t))] assert checksysodesol(eq1, sol1) == (True, [0, 0, 0]) eq2 = (Eq(diff(x(t),t),3*y(t)-11*z(t)),Eq(diff(y(t),t),7*z(t)-3*x(t)),Eq(diff(z(t),t),11*x(t)-7*y(t))) sol2 = [Eq(x(t), 7*C0 + sqrt(179)*C1*cos(sqrt(179)*t) + (77*C1/3 + 130*C2/3)*sin(sqrt(179)*t)), \ Eq(y(t), 11*C0 + sqrt(179)*C2*cos(sqrt(179)*t) + (-58*C1/3 - 77*C2/3)*sin(sqrt(179)*t)), \ Eq(z(t), 3*C0 + sqrt(179)*(-7*C1/3 - 11*C2/3)*cos(sqrt(179)*t) + (11*C1 - 7*C2)*sin(sqrt(179)*t))] assert checksysodesol(eq2, sol2) == (True, [0, 0, 0]) eq3 = (Eq(3*diff(x(t),t),4*5*(y(t)-z(t))),Eq(4*diff(y(t),t),3*5*(z(t)-x(t))),Eq(5*diff(z(t),t),3*4*(x(t)-y(t)))) sol3 = [Eq(x(t), C0 + 5*sqrt(2)*C1*cos(5*sqrt(2)*t) + (12*C1/5 + 164*C2/15)*sin(5*sqrt(2)*t)), \ Eq(y(t), C0 + 5*sqrt(2)*C2*cos(5*sqrt(2)*t) + (-51*C1/10 - 12*C2/5)*sin(5*sqrt(2)*t)), \ Eq(z(t), C0 + 5*sqrt(2)*(-9*C1/25 - 16*C2/25)*cos(5*sqrt(2)*t) + (12*C1/5 - 12*C2/5)*sin(5*sqrt(2)*t))] assert checksysodesol(eq3, sol3) == (True, [0, 0, 0]) f = t**3 + log(t) g = t**2 + sin(t) eq4 = (Eq(diff(x(t),t),(4*f+g)*x(t)-f*y(t)-2*f*z(t)), Eq(diff(y(t),t),2*f*x(t)+(f+g)*y(t)-2*f*z(t)), Eq(diff(z(t),t),5*f*x(t)+f*y(t)+(-3*f+g)*z(t))) sol4 = [Eq(x(t), (C1*exp(-2*Integral(t**3 + log(t), t)) + C2*(sqrt(3)*sin(sqrt(3)*Integral(t**3 + log(t), t))/6 \ + cos(sqrt(3)*Integral(t**3 + log(t), t))/2) + C3*(sin(sqrt(3)*Integral(t**3 + log(t), t))/2 - \ sqrt(3)*cos(sqrt(3)*Integral(t**3 + log(t), t))/6))*exp(Integral(-t**2 - sin(t), t))), Eq(y(t), \ (C2*(sqrt(3)*sin(sqrt(3)*Integral(t**3 + log(t), t))/6 + cos(sqrt(3)*Integral(t**3 + log(t), t))/2) + \ C3*(sin(sqrt(3)*Integral(t**3 + log(t), t))/2 - sqrt(3)*cos(sqrt(3)*Integral(t**3 + log(t), t))/6))*\ exp(Integral(-t**2 - sin(t), t))), Eq(z(t), (C1*exp(-2*Integral(t**3 + log(t), t)) + C2*cos(sqrt(3)*\ Integral(t**3 + log(t), t)) + C3*sin(sqrt(3)*Integral(t**3 + log(t), t)))*exp(Integral(-t**2 - sin(t), t)))] assert dsolve(eq4) == sol4 # FIXME: assert checksysodesol(eq4, sol4) == (True, [0, 0, 0]) # this one fails eq5 = (Eq(diff(x(t),t),4*x(t) - z(t)),Eq(diff(y(t),t),2*x(t)+2*y(t)-z(t)),Eq(diff(z(t),t),3*x(t)+y(t))) sol5 = [Eq(x(t), C1*exp(2*t) + C2*t*exp(2*t) + C2*exp(2*t) + C3*t**2*exp(2*t)/2 + C3*t*exp(2*t) + C3*exp(2*t)), \ Eq(y(t), C1*exp(2*t) + C2*t*exp(2*t) + C2*exp(2*t) + C3*t**2*exp(2*t)/2 + C3*t*exp(2*t)), \ Eq(z(t), 2*C1*exp(2*t) + 2*C2*t*exp(2*t) + C2*exp(2*t) + C3*t**2*exp(2*t) + C3*t*exp(2*t) + C3*exp(2*t))] assert checksysodesol(eq5, sol5) == (True, [0, 0, 0]) eq6 = (Eq(diff(x(t),t),4*x(t) - y(t) - 2*z(t)),Eq(diff(y(t),t),2*x(t) + y(t)- 2*z(t)),Eq(diff(z(t),t),5*x(t)-3*z(t))) sol6 = [Eq(x(t), C1*exp(2*t) + C2*(-sin(t)/5 + 3*cos(t)/5) + C3*(3*sin(t)/5 + cos(t)/5)), Eq(y(t), C2*(-sin(t)/5 + 3*cos(t)/5) + C3*(3*sin(t)/5 + cos(t)/5)), Eq(z(t), C1*exp(2*t) + C2*cos(t) + C3*sin(t))] assert checksysodesol(eq5, sol5) == (True, [0, 0, 0]) def test_linear_3eq_order1_nonhomog(): e = [Eq(diff(f(x), x), -9*f(x) - 4*g(x)), Eq(diff(g(x), x), -4*g(x)), Eq(diff(h(x), x), h(x) + exp(x))] raises(NotImplementedError, lambda: dsolve(e)) @XFAIL def test_linear_3eq_order1_diagonal(): # code makes assumptions about coefficients being nonzero, breaks when assumptions are not true e = [Eq(diff(f(x), x), f(x)), Eq(diff(g(x), x), g(x)), Eq(diff(h(x), x), h(x))] s1 = [Eq(f(x), C1*exp(x)), Eq(g(x), C2*exp(x)), Eq(h(x), C3*exp(x))] s = dsolve(e) assert s == s1 assert checksysodesol(e, s1) == (True, [0, 0, 0]) def test_nonlinear_2eq_order1(): x, y, z = symbols('x, y, z', cls=Function) t = Symbol('t') eq1 = (Eq(diff(x(t),t),x(t)*y(t)**3), Eq(diff(y(t),t),y(t)**5)) sol1 = [ Eq(x(t), C1*exp((-1/(4*C2 + 4*t))**(-S(1)/4))), Eq(y(t), -(-1/(4*C2 + 4*t))**(S(1)/4)), Eq(x(t), C1*exp(-1/(-1/(4*C2 + 4*t))**(S(1)/4))), Eq(y(t), (-1/(4*C2 + 4*t))**(S(1)/4)), Eq(x(t), C1*exp(-I/(-1/(4*C2 + 4*t))**(S(1)/4))), Eq(y(t), -I*(-1/(4*C2 + 4*t))**(S(1)/4)), Eq(x(t), C1*exp(I/(-1/(4*C2 + 4*t))**(S(1)/4))), Eq(y(t), I*(-1/(4*C2 + 4*t))**(S(1)/4))] assert dsolve(eq1) == sol1 assert checksysodesol(eq1, sol1) == (True, [0, 0]) eq2 = (Eq(diff(x(t),t), exp(3*x(t))*y(t)**3),Eq(diff(y(t),t), y(t)**5)) sol2 = [ Eq(x(t), -log(C1 - 3/(-1/(4*C2 + 4*t))**(S(1)/4))/3), Eq(y(t), -(-1/(4*C2 + 4*t))**(S(1)/4)), Eq(x(t), -log(C1 + 3/(-1/(4*C2 + 4*t))**(S(1)/4))/3), Eq(y(t), (-1/(4*C2 + 4*t))**(S(1)/4)), Eq(x(t), -log(C1 + 3*I/(-1/(4*C2 + 4*t))**(S(1)/4))/3), Eq(y(t), -I*(-1/(4*C2 + 4*t))**(S(1)/4)), Eq(x(t), -log(C1 - 3*I/(-1/(4*C2 + 4*t))**(S(1)/4))/3), Eq(y(t), I*(-1/(4*C2 + 4*t))**(S(1)/4))] assert dsolve(eq2) == sol2 assert checksysodesol(eq2, sol2) == (True, [0, 0]) eq3 = (Eq(diff(x(t),t), y(t)*x(t)), Eq(diff(y(t),t), x(t)**3)) tt = S(2)/3 sol3 = [ Eq(x(t), 6**tt/(6*(-sinh(sqrt(C1)*(C2 + t)/2)/sqrt(C1))**tt)), Eq(y(t), sqrt(C1 + C1/sinh(sqrt(C1)*(C2 + t)/2)**2)/3)] assert dsolve(eq3) == sol3 # FIXME: assert checksysodesol(eq3, sol3) == (True, [0, 0]) eq4 = (Eq(diff(x(t),t),x(t)*y(t)*sin(t)**2), Eq(diff(y(t),t),y(t)**2*sin(t)**2)) sol4 = set([Eq(x(t), -2*exp(C1)/(C2*exp(C1) + t - sin(2*t)/2)), Eq(y(t), -2/(C1 + t - sin(2*t)/2))]) assert dsolve(eq4) == sol4 # FIXME: assert checksysodesol(eq4, sol4) == (True, [0, 0]) eq5 = (Eq(x(t),t*diff(x(t),t)+diff(x(t),t)*diff(y(t),t)), Eq(y(t),t*diff(y(t),t)+diff(y(t),t)**2)) sol5 = set([Eq(x(t), C1*C2 + C1*t), Eq(y(t), C2**2 + C2*t)]) assert dsolve(eq5) == sol5 assert checksysodesol(eq5, sol5) == (True, [0, 0]) eq6 = (Eq(diff(x(t),t),x(t)**2*y(t)**3), Eq(diff(y(t),t),y(t)**5)) sol6 = [ Eq(x(t), 1/(C1 - 1/(-1/(4*C2 + 4*t))**(S(1)/4))), Eq(y(t), -(-1/(4*C2 + 4*t))**(S(1)/4)), Eq(x(t), 1/(C1 + (-1/(4*C2 + 4*t))**(-S(1)/4))), Eq(y(t), (-1/(4*C2 + 4*t))**(S(1)/4)), Eq(x(t), 1/(C1 + I/(-1/(4*C2 + 4*t))**(S(1)/4))), Eq(y(t), -I*(-1/(4*C2 + 4*t))**(S(1)/4)), Eq(x(t), 1/(C1 - I/(-1/(4*C2 + 4*t))**(S(1)/4))), Eq(y(t), I*(-1/(4*C2 + 4*t))**(S(1)/4))] assert dsolve(eq6) == sol6 assert checksysodesol(eq6, sol6) == (True, [0, 0]) def test_checksysodesol(): x, y, z = symbols('x, y, z', cls=Function) t = Symbol('t') eq = (Eq(diff(x(t),t), 9*y(t)), Eq(diff(y(t),t), 12*x(t))) sol = [Eq(x(t), 9*C1*exp(-6*sqrt(3)*t) + 9*C2*exp(6*sqrt(3)*t)), \ Eq(y(t), -6*sqrt(3)*C1*exp(-6*sqrt(3)*t) + 6*sqrt(3)*C2*exp(6*sqrt(3)*t))] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t), 2*x(t) + 4*y(t)), Eq(diff(y(t),t), 12*x(t) + 41*y(t))) sol = [Eq(x(t), 4*C1*exp(t*(-sqrt(1713)/2 + S(43)/2)) + 4*C2*exp(t*(sqrt(1713)/2 + \ S(43)/2))), Eq(y(t), C1*(-sqrt(1713)/2 + S(39)/2)*exp(t*(-sqrt(1713)/2 + \ S(43)/2)) + C2*(S(39)/2 + sqrt(1713)/2)*exp(t*(sqrt(1713)/2 + S(43)/2)))] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t), x(t) + y(t)), Eq(diff(y(t),t), -2*x(t) + 2*y(t))) sol = [Eq(x(t), (C1*sin(sqrt(7)*t/2) + C2*cos(sqrt(7)*t/2))*exp(3*t/2)), \ Eq(y(t), ((C1/2 - sqrt(7)*C2/2)*sin(sqrt(7)*t/2) + (sqrt(7)*C1/2 + \ C2/2)*cos(sqrt(7)*t/2))*exp(3*t/2))] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t), x(t) + y(t) + 9), Eq(diff(y(t),t), 2*x(t) + 5*y(t) + 23)) sol = [Eq(x(t), C1*exp(t*(-sqrt(6) + 3)) + C2*exp(t*(sqrt(6) + 3)) - \ S(22)/3), Eq(y(t), C1*(-sqrt(6) + 2)*exp(t*(-sqrt(6) + 3)) + C2*(2 + \ sqrt(6))*exp(t*(sqrt(6) + 3)) - S(5)/3)] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t), x(t) + y(t) + 81), Eq(diff(y(t),t), -2*x(t) + y(t) + 23)) sol = [Eq(x(t), (C1*sin(sqrt(2)*t) + C2*cos(sqrt(2)*t))*exp(t) - S(58)/3), \ Eq(y(t), (sqrt(2)*C1*cos(sqrt(2)*t) - sqrt(2)*C2*sin(sqrt(2)*t))*exp(t) - S(185)/3)] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t), 5*t*x(t) + 2*y(t)), Eq(diff(y(t),t), 2*x(t) + 5*t*y(t))) sol = [Eq(x(t), (C1*exp((Integral(2, t).doit())) + C2*exp(-(Integral(2, t)).doit()))*\ exp((Integral(5*t, t)).doit())), Eq(y(t), (C1*exp((Integral(2, t)).doit()) - \ C2*exp(-(Integral(2, t)).doit()))*exp((Integral(5*t, t)).doit()))] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t), 5*t*x(t) + t**2*y(t)), Eq(diff(y(t),t), -t**2*x(t) + 5*t*y(t))) sol = [Eq(x(t), (C1*cos((Integral(t**2, t)).doit()) + C2*sin((Integral(t**2, t)).doit()))*\ exp((Integral(5*t, t)).doit())), Eq(y(t), (-C1*sin((Integral(t**2, t)).doit()) + \ C2*cos((Integral(t**2, t)).doit()))*exp((Integral(5*t, t)).doit()))] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t), 5*t*x(t) + t**2*y(t)), Eq(diff(y(t),t), -t**2*x(t) + (5*t+9*t**2)*y(t))) sol = [Eq(x(t), (C1*exp((-sqrt(77)/2 + S(9)/2)*(Integral(t**2, t)).doit()) + \ C2*exp((sqrt(77)/2 + S(9)/2)*(Integral(t**2, t)).doit()))*exp((Integral(5*t, t)).doit())), \ Eq(y(t), (C1*(-sqrt(77)/2 + S(9)/2)*exp((-sqrt(77)/2 + S(9)/2)*(Integral(t**2, t)).doit()) + \ C2*(sqrt(77)/2 + S(9)/2)*exp((sqrt(77)/2 + S(9)/2)*(Integral(t**2, t)).doit()))*exp((Integral(5*t, t)).doit()))] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t,t), 5*x(t) + 43*y(t)), Eq(diff(y(t),t,t), x(t) + 9*y(t))) root0 = -sqrt(-sqrt(47) + 7) root1 = sqrt(-sqrt(47) + 7) root2 = -sqrt(sqrt(47) + 7) root3 = sqrt(sqrt(47) + 7) sol = [Eq(x(t), 43*C1*exp(t*root0) + 43*C2*exp(t*root1) + 43*C3*exp(t*root2) + 43*C4*exp(t*root3)), \ Eq(y(t), C1*(root0**2 - 5)*exp(t*root0) + C2*(root1**2 - 5)*exp(t*root1) + \ C3*(root2**2 - 5)*exp(t*root2) + C4*(root3**2 - 5)*exp(t*root3))] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t,t), 8*x(t)+3*y(t)+31), Eq(diff(y(t),t,t), 9*x(t)+7*y(t)+12)) root0 = -sqrt(-sqrt(109)/2 + S(15)/2) root1 = sqrt(-sqrt(109)/2 + S(15)/2) root2 = -sqrt(sqrt(109)/2 + S(15)/2) root3 = sqrt(sqrt(109)/2 + S(15)/2) sol = [Eq(x(t), 3*C1*exp(t*root0) + 3*C2*exp(t*root1) + 3*C3*exp(t*root2) + 3*C4*exp(t*root3) - S(181)/29), \ Eq(y(t), C1*(root0**2 - 8)*exp(t*root0) + C2*(root1**2 - 8)*exp(t*root1) + \ C3*(root2**2 - 8)*exp(t*root2) + C4*(root3**2 - 8)*exp(t*root3) + S(183)/29)] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t,t) - 9*diff(y(t),t) + 7*x(t),0), Eq(diff(y(t),t,t) + 9*diff(x(t),t) + 7*y(t),0)) sol = [Eq(x(t), C1*cos(t*(S(9)/2 + sqrt(109)/2)) + C2*sin(t*(S(9)/2 + sqrt(109)/2)) + \ C3*cos(t*(-sqrt(109)/2 + S(9)/2)) + C4*sin(t*(-sqrt(109)/2 + S(9)/2))), Eq(y(t), -C1*sin(t*(S(9)/2 + sqrt(109)/2)) \ + C2*cos(t*(S(9)/2 + sqrt(109)/2)) - C3*sin(t*(-sqrt(109)/2 + S(9)/2)) + C4*cos(t*(-sqrt(109)/2 + S(9)/2)))] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t,t), 9*t*diff(y(t),t)-9*y(t)), Eq(diff(y(t),t,t),7*t*diff(x(t),t)-7*x(t))) I1 = sqrt(6)*7**(S(1)/4)*sqrt(pi)*erfi(sqrt(6)*7**(S(1)/4)*t/2)/2 - exp(3*sqrt(7)*t**2/2)/t I2 = -sqrt(6)*7**(S(1)/4)*sqrt(pi)*erf(sqrt(6)*7**(S(1)/4)*t/2)/2 - exp(-3*sqrt(7)*t**2/2)/t sol = [Eq(x(t), C3*t + t*(9*C1*I1 + 9*C2*I2)), Eq(y(t), C4*t + t*(3*sqrt(7)*C1*I1 - 3*sqrt(7)*C2*I2))] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t), 21*x(t)), Eq(diff(y(t),t), 17*x(t)+3*y(t)), Eq(diff(z(t),t), 5*x(t)+7*y(t)+9*z(t))) sol = [Eq(x(t), C1*exp(21*t)), Eq(y(t), 17*C1*exp(21*t)/18 + C2*exp(3*t)), \ Eq(z(t), 209*C1*exp(21*t)/216 - 7*C2*exp(3*t)/6 + C3*exp(9*t))] assert checksysodesol(eq, sol) == (True, [0, 0, 0]) eq = (Eq(diff(x(t),t),3*y(t)-11*z(t)),Eq(diff(y(t),t),7*z(t)-3*x(t)),Eq(diff(z(t),t),11*x(t)-7*y(t))) sol = [Eq(x(t), 7*C0 + sqrt(179)*C1*cos(sqrt(179)*t) + (77*C1/3 + 130*C2/3)*sin(sqrt(179)*t)), \ Eq(y(t), 11*C0 + sqrt(179)*C2*cos(sqrt(179)*t) + (-58*C1/3 - 77*C2/3)*sin(sqrt(179)*t)), \ Eq(z(t), 3*C0 + sqrt(179)*(-7*C1/3 - 11*C2/3)*cos(sqrt(179)*t) + (11*C1 - 7*C2)*sin(sqrt(179)*t))] assert checksysodesol(eq, sol) == (True, [0, 0, 0]) eq = (Eq(3*diff(x(t),t),4*5*(y(t)-z(t))),Eq(4*diff(y(t),t),3*5*(z(t)-x(t))),Eq(5*diff(z(t),t),3*4*(x(t)-y(t)))) sol = [Eq(x(t), C0 + 5*sqrt(2)*C1*cos(5*sqrt(2)*t) + (12*C1/5 + 164*C2/15)*sin(5*sqrt(2)*t)), \ Eq(y(t), C0 + 5*sqrt(2)*C2*cos(5*sqrt(2)*t) + (-51*C1/10 - 12*C2/5)*sin(5*sqrt(2)*t)), \ Eq(z(t), C0 + 5*sqrt(2)*(-9*C1/25 - 16*C2/25)*cos(5*sqrt(2)*t) + (12*C1/5 - 12*C2/5)*sin(5*sqrt(2)*t))] assert checksysodesol(eq, sol) == (True, [0, 0, 0]) eq = (Eq(diff(x(t),t),4*x(t) - z(t)),Eq(diff(y(t),t),2*x(t)+2*y(t)-z(t)),Eq(diff(z(t),t),3*x(t)+y(t))) sol = [Eq(x(t), C1*exp(2*t) + C2*t*exp(2*t) + C2*exp(2*t) + C3*t**2*exp(2*t)/2 + C3*t*exp(2*t) + C3*exp(2*t)), \ Eq(y(t), C1*exp(2*t) + C2*t*exp(2*t) + C2*exp(2*t) + C3*t**2*exp(2*t)/2 + C3*t*exp(2*t)), \ Eq(z(t), 2*C1*exp(2*t) + 2*C2*t*exp(2*t) + C2*exp(2*t) + C3*t**2*exp(2*t) + C3*t*exp(2*t) + C3*exp(2*t))] assert checksysodesol(eq, sol) == (True, [0, 0, 0]) eq = (Eq(diff(x(t),t),4*x(t) - y(t) - 2*z(t)),Eq(diff(y(t),t),2*x(t) + y(t)- 2*z(t)),Eq(diff(z(t),t),5*x(t)-3*z(t))) sol = [Eq(x(t), C1*exp(2*t) + C2*(-sin(t) + 3*cos(t)) + C3*(3*sin(t) + cos(t))), \ Eq(y(t), C2*(-sin(t) + 3*cos(t)) + C3*(3*sin(t) + cos(t))), Eq(z(t), C1*exp(2*t) + 5*C2*cos(t) + 5*C3*sin(t))] assert checksysodesol(eq, sol) == (True, [0, 0, 0]) eq = (Eq(diff(x(t),t),x(t)*y(t)**3), Eq(diff(y(t),t),y(t)**5)) sol = [Eq(x(t), C1*exp((-1/(4*C2 + 4*t))**(-S(1)/4))), Eq(y(t), -(-1/(4*C2 + 4*t))**(S(1)/4)), \ Eq(x(t), C1*exp(-1/(-1/(4*C2 + 4*t))**(S(1)/4))), Eq(y(t), (-1/(4*C2 + 4*t))**(S(1)/4)), \ Eq(x(t), C1*exp(-I/(-1/(4*C2 + 4*t))**(S(1)/4))), Eq(y(t), -I*(-1/(4*C2 + 4*t))**(S(1)/4)), \ Eq(x(t), C1*exp(I/(-1/(4*C2 + 4*t))**(S(1)/4))), Eq(y(t), I*(-1/(4*C2 + 4*t))**(S(1)/4))] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(diff(x(t),t), exp(3*x(t))*y(t)**3),Eq(diff(y(t),t), y(t)**5)) sol = [Eq(x(t), -log(C1 - 3/(-1/(4*C2 + 4*t))**(S(1)/4))/3), Eq(y(t), -(-1/(4*C2 + 4*t))**(S(1)/4)), \ Eq(x(t), -log(C1 + 3/(-1/(4*C2 + 4*t))**(S(1)/4))/3), Eq(y(t), (-1/(4*C2 + 4*t))**(S(1)/4)), \ Eq(x(t), -log(C1 + 3*I/(-1/(4*C2 + 4*t))**(S(1)/4))/3), Eq(y(t), -I*(-1/(4*C2 + 4*t))**(S(1)/4)), \ Eq(x(t), -log(C1 - 3*I/(-1/(4*C2 + 4*t))**(S(1)/4))/3), Eq(y(t), I*(-1/(4*C2 + 4*t))**(S(1)/4))] assert checksysodesol(eq, sol) == (True, [0, 0]) eq = (Eq(x(t),t*diff(x(t),t)+diff(x(t),t)*diff(y(t),t)), Eq(y(t),t*diff(y(t),t)+diff(y(t),t)**2)) sol = set([Eq(x(t), C1*C2 + C1*t), Eq(y(t), C2**2 + C2*t)]) assert checksysodesol(eq, sol) == (True, [0, 0]) @slow def test_nonlinear_3eq_order1(): x, y, z = symbols('x, y, z', cls=Function) t, u = symbols('t u') eq1 = (4*diff(x(t),t) + 2*y(t)*z(t), 3*diff(y(t),t) - z(t)*x(t), 5*diff(z(t),t) - x(t)*y(t)) sol1 = [Eq(4*Integral(1/(sqrt(-4*u**2 - 3*C1 + C2)*sqrt(-4*u**2 + 5*C1 - C2)), (u, x(t))), C3 - sqrt(15)*t/15), Eq(3*Integral(1/(sqrt(-6*u**2 - C1 + 5*C2)*sqrt(3*u**2 + C1 - 4*C2)), (u, y(t))), C3 + sqrt(5)*t/10), Eq(5*Integral(1/(sqrt(-10*u**2 - 3*C1 + C2)* sqrt(5*u**2 + 4*C1 - C2)), (u, z(t))), C3 + sqrt(3)*t/6)] assert [i.dummy_eq(j) for i, j in zip(dsolve(eq1), sol1)] # FIXME: assert checksysodesol(eq1, sol1) == (True, [0, 0, 0]) eq2 = (4*diff(x(t),t) + 2*y(t)*z(t)*sin(t), 3*diff(y(t),t) - z(t)*x(t)*sin(t), 5*diff(z(t),t) - x(t)*y(t)*sin(t)) sol2 = [Eq(3*Integral(1/(sqrt(-6*u**2 - C1 + 5*C2)*sqrt(3*u**2 + C1 - 4*C2)), (u, x(t))), C3 + sqrt(5)*cos(t)/10), Eq(4*Integral(1/(sqrt(-4*u**2 - 3*C1 + C2)*sqrt(-4*u**2 + 5*C1 - C2)), (u, y(t))), C3 - sqrt(15)*cos(t)/15), Eq(5*Integral(1/(sqrt(-10*u**2 - 3*C1 + C2)* sqrt(5*u**2 + 4*C1 - C2)), (u, z(t))), C3 + sqrt(3)*cos(t)/6)] assert [i.dummy_eq(j) for i, j in zip(dsolve(eq2), sol2)] # FIXME: assert checksysodesol(eq2, sol2) == (True, [0, 0, 0]) @slow def test_checkodesol(): from sympy import Ei # For the most part, checkodesol is well tested in the tests below. # These tests only handle cases not checked below. raises(ValueError, lambda: checkodesol(f(x, y).diff(x), Eq(f(x, y), x))) raises(ValueError, lambda: checkodesol(f(x).diff(x), Eq(f(x, y), x), f(x, y))) assert checkodesol(f(x).diff(x), Eq(f(x, y), x)) == \ (False, -f(x).diff(x) + f(x, y).diff(x) - 1) assert checkodesol(f(x).diff(x), Eq(f(x), x)) is not True assert checkodesol(f(x).diff(x), Eq(f(x), x)) == (False, 1) sol1 = Eq(f(x)**5 + 11*f(x) - 2*f(x) + x, 0) assert checkodesol(diff(sol1.lhs, x), sol1) == (True, 0) assert checkodesol(diff(sol1.lhs, x)*exp(f(x)), sol1) == (True, 0) assert checkodesol(diff(sol1.lhs, x, 2), sol1) == (True, 0) assert checkodesol(diff(sol1.lhs, x, 2)*exp(f(x)), sol1) == (True, 0) assert checkodesol(diff(sol1.lhs, x, 3), sol1) == (True, 0) assert checkodesol(diff(sol1.lhs, x, 3)*exp(f(x)), sol1) == (True, 0) assert checkodesol(diff(sol1.lhs, x, 3), Eq(f(x), x*log(x))) == \ (False, 60*x**4*((log(x) + 1)**2 + log(x))*( log(x) + 1)*log(x)**2 - 5*x**4*log(x)**4 - 9) assert checkodesol(diff(exp(f(x)) + x, x)*x, Eq(exp(f(x)) + x)) == \ (True, 0) assert checkodesol(diff(exp(f(x)) + x, x)*x, Eq(exp(f(x)) + x), solve_for_func=False) == (True, 0) assert checkodesol(f(x).diff(x, 2), [Eq(f(x), C1 + C2*x), Eq(f(x), C2 + C1*x), Eq(f(x), C1*x + C2*x**2)]) == \ [(True, 0), (True, 0), (False, C2)] assert checkodesol(f(x).diff(x, 2), set([Eq(f(x), C1 + C2*x), Eq(f(x), C2 + C1*x), Eq(f(x), C1*x + C2*x**2)])) == \ set([(True, 0), (True, 0), (False, C2)]) assert checkodesol(f(x).diff(x) - 1/f(x)/2, Eq(f(x)**2, x)) == \ [(True, 0), (True, 0)] assert checkodesol(f(x).diff(x) - f(x), Eq(C1*exp(x), f(x))) == (True, 0) # Based on test_1st_homogeneous_coeff_ode2_eq3sol. Make sure that # checkodesol tries back substituting f(x) when it can. eq3 = x*exp(f(x)/x) + f(x) - x*f(x).diff(x) sol3 = Eq(f(x), log(log(C1/x)**(-x))) assert not checkodesol(eq3, sol3)[1].has(f(x)) # This case was failing intermittently depending on hash-seed: eqn = Eq(Derivative(x*Derivative(f(x), x), x)/x, exp(x)) sol = Eq(f(x), C1 + C2*log(x) + exp(x) - Ei(x)) assert checkodesol(eqn, sol, order=2, solve_for_func=False)[0] @slow def test_dsolve_options(): eq = x*f(x).diff(x) + f(x) a = dsolve(eq, hint='all') b = dsolve(eq, hint='all', simplify=False) c = dsolve(eq, hint='all_Integral') keys = ['1st_exact', '1st_exact_Integral', '1st_homogeneous_coeff_best', '1st_homogeneous_coeff_subs_dep_div_indep', '1st_homogeneous_coeff_subs_dep_div_indep_Integral', '1st_homogeneous_coeff_subs_indep_div_dep', '1st_homogeneous_coeff_subs_indep_div_dep_Integral', '1st_linear', '1st_linear_Integral', 'almost_linear', 'almost_linear_Integral', 'best', 'best_hint', 'default', 'lie_group', 'nth_linear_euler_eq_homogeneous', 'order', 'separable', 'separable_Integral'] Integral_keys = ['1st_exact_Integral', '1st_homogeneous_coeff_subs_dep_div_indep_Integral', '1st_homogeneous_coeff_subs_indep_div_dep_Integral', '1st_linear_Integral', 'almost_linear_Integral', 'best', 'best_hint', 'default', 'nth_linear_euler_eq_homogeneous', 'order', 'separable_Integral'] assert sorted(a.keys()) == keys assert a['order'] == ode_order(eq, f(x)) assert a['best'] == Eq(f(x), C1/x) assert dsolve(eq, hint='best') == Eq(f(x), C1/x) assert a['default'] == 'separable' assert a['best_hint'] == 'separable' assert not a['1st_exact'].has(Integral) assert not a['separable'].has(Integral) assert not a['1st_homogeneous_coeff_best'].has(Integral) assert not a['1st_homogeneous_coeff_subs_dep_div_indep'].has(Integral) assert not a['1st_homogeneous_coeff_subs_indep_div_dep'].has(Integral) assert not a['1st_linear'].has(Integral) assert a['1st_linear_Integral'].has(Integral) assert a['1st_exact_Integral'].has(Integral) assert a['1st_homogeneous_coeff_subs_dep_div_indep_Integral'].has(Integral) assert a['1st_homogeneous_coeff_subs_indep_div_dep_Integral'].has(Integral) assert a['separable_Integral'].has(Integral) assert sorted(b.keys()) == keys assert b['order'] == ode_order(eq, f(x)) assert b['best'] == Eq(f(x), C1/x) assert dsolve(eq, hint='best', simplify=False) == Eq(f(x), C1/x) assert b['default'] == 'separable' assert b['best_hint'] == '1st_linear' assert a['separable'] != b['separable'] assert a['1st_homogeneous_coeff_subs_dep_div_indep'] != \ b['1st_homogeneous_coeff_subs_dep_div_indep'] assert a['1st_homogeneous_coeff_subs_indep_div_dep'] != \ b['1st_homogeneous_coeff_subs_indep_div_dep'] assert not b['1st_exact'].has(Integral) assert not b['separable'].has(Integral) assert not b['1st_homogeneous_coeff_best'].has(Integral) assert not b['1st_homogeneous_coeff_subs_dep_div_indep'].has(Integral) assert not b['1st_homogeneous_coeff_subs_indep_div_dep'].has(Integral) assert not b['1st_linear'].has(Integral) assert b['1st_linear_Integral'].has(Integral) assert b['1st_exact_Integral'].has(Integral) assert b['1st_homogeneous_coeff_subs_dep_div_indep_Integral'].has(Integral) assert b['1st_homogeneous_coeff_subs_indep_div_dep_Integral'].has(Integral) assert b['separable_Integral'].has(Integral) assert sorted(c.keys()) == Integral_keys raises(ValueError, lambda: dsolve(eq, hint='notarealhint')) raises(ValueError, lambda: dsolve(eq, hint='Liouville')) assert dsolve(f(x).diff(x) - 1/f(x)**2, hint='all')['best'] == \ dsolve(f(x).diff(x) - 1/f(x)**2, hint='best') assert dsolve(f(x) + f(x).diff(x) + sin(x).diff(x) + 1, f(x), hint="1st_linear_Integral") == \ Eq(f(x), (C1 + Integral((-sin(x).diff(x) - 1)* exp(Integral(1, x)), x))*exp(-Integral(1, x))) def test_classify_ode(): assert classify_ode(f(x).diff(x, 2), f(x)) == \ ( 'nth_algebraic', 'nth_linear_constant_coeff_homogeneous', 'nth_linear_euler_eq_homogeneous', 'Liouville', '2nd_power_series_ordinary', 'nth_algebraic_Integral', 'Liouville_Integral', ) assert classify_ode(f(x), f(x)) == () assert classify_ode(Eq(f(x).diff(x), 0), f(x)) == ( 'nth_algebraic', 'separable', '1st_linear', '1st_homogeneous_coeff_best', '1st_homogeneous_coeff_subs_indep_div_dep', '1st_homogeneous_coeff_subs_dep_div_indep', '1st_power_series', 'lie_group', 'nth_linear_constant_coeff_homogeneous', 'nth_linear_euler_eq_homogeneous', 'nth_algebraic_Integral', 'separable_Integral', '1st_linear_Integral', '1st_homogeneous_coeff_subs_indep_div_dep_Integral', '1st_homogeneous_coeff_subs_dep_div_indep_Integral') assert classify_ode(f(x).diff(x)**2, f(x)) == ( 'nth_algebraic', 'lie_group', 'nth_algebraic_Integral') # issue 4749: f(x) should be cleared from highest derivative before classifying a = classify_ode(Eq(f(x).diff(x) + f(x), x), f(x)) b = classify_ode(f(x).diff(x)*f(x) + f(x)*f(x) - x*f(x), f(x)) c = classify_ode(f(x).diff(x)/f(x) + f(x)/f(x) - x/f(x), f(x)) assert a == ('1st_linear', 'Bernoulli', 'almost_linear', '1st_power_series', "lie_group", 'nth_linear_constant_coeff_undetermined_coefficients', 'nth_linear_constant_coeff_variation_of_parameters', '1st_linear_Integral', 'Bernoulli_Integral', 'almost_linear_Integral', 'nth_linear_constant_coeff_variation_of_parameters_Integral') assert b == c != () assert classify_ode( 2*x*f(x)*f(x).diff(x) + (1 + x)*f(x)**2 - exp(x), f(x) ) == ('Bernoulli', 'almost_linear', 'lie_group', 'Bernoulli_Integral', 'almost_linear_Integral') assert 'Riccati_special_minus2' in \ classify_ode(2*f(x).diff(x) + f(x)**2 - f(x)/x + 3*x**(-2), f(x)) raises(ValueError, lambda: classify_ode(x + f(x, y).diff(x).diff( y), f(x, y))) # issue 5176 k = Symbol('k') assert classify_ode(f(x).diff(x)/(k*f(x) + k*x*f(x)) + 2*f(x)/(k*f(x) + k*x*f(x)) + x*f(x).diff(x)/(k*f(x) + k*x*f(x)) + z, f(x)) == \ ('separable', '1st_exact', '1st_power_series', 'lie_group', 'separable_Integral', '1st_exact_Integral') # preprocessing ans = ('nth_algebraic', 'separable', '1st_exact', '1st_linear', 'Bernoulli', '1st_homogeneous_coeff_best', '1st_homogeneous_coeff_subs_indep_div_dep', '1st_homogeneous_coeff_subs_dep_div_indep', '1st_power_series', 'lie_group', 'nth_linear_constant_coeff_undetermined_coefficients', 'nth_linear_euler_eq_nonhomogeneous_undetermined_coefficients', 'nth_linear_constant_coeff_variation_of_parameters', 'nth_linear_euler_eq_nonhomogeneous_variation_of_parameters', 'nth_algebraic_Integral', 'separable_Integral', '1st_exact_Integral', '1st_linear_Integral', 'Bernoulli_Integral', '1st_homogeneous_coeff_subs_indep_div_dep_Integral', '1st_homogeneous_coeff_subs_dep_div_indep_Integral', 'nth_linear_constant_coeff_variation_of_parameters_Integral', 'nth_linear_euler_eq_nonhomogeneous_variation_of_parameters_Integral') # w/o f(x) given assert classify_ode(diff(f(x) + x, x) + diff(f(x), x)) == ans # w/ f(x) and prep=True assert classify_ode(diff(f(x) + x, x) + diff(f(x), x), f(x), prep=True) == ans assert classify_ode(Eq(2*x**3*f(x).diff(x), 0), f(x)) == \ ('nth_algebraic', 'separable', '1st_linear', '1st_power_series', 'lie_group', 'nth_linear_euler_eq_homogeneous', 'nth_algebraic_Integral', 'separable_Integral', '1st_linear_Integral') assert classify_ode(Eq(2*f(x)**3*f(x).diff(x), 0), f(x)) == \ ('nth_algebraic', 'separable', '1st_power_series', 'lie_group', 'nth_algebraic_Integral', 'separable_Integral') # test issue 13864 assert classify_ode(Eq(diff(f(x), x) - f(x)**x, 0), f(x)) == \ ('1st_power_series', 'lie_group') assert isinstance(classify_ode(Eq(f(x), 5), f(x), dict=True), dict) def test_classify_ode_ics(): # Dummy eq = f(x).diff(x, x) - f(x) # Not f(0) or f'(0) ics = {x: 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) ############################ # f(0) type (AppliedUndef) # ############################ # Wrong function ics = {g(0): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Contains x ics = {f(x): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Too many args ics = {f(0, 0): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # point contains f # XXX: Should be NotImplementedError ics = {f(0): f(1)} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Does not raise ics = {f(0): 1} classify_ode(eq, f(x), ics=ics) ##################### # f'(0) type (Subs) # ##################### # Wrong function ics = {g(x).diff(x).subs(x, 0): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Contains x ics = {f(y).diff(y).subs(y, x): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Wrong variable ics = {f(y).diff(y).subs(y, 0): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Too many args ics = {f(x, y).diff(x).subs(x, 0): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Derivative wrt wrong vars ics = {Derivative(f(x), x, y).subs(x, 0): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # point contains f # XXX: Should be NotImplementedError ics = {f(x).diff(x).subs(x, 0): f(0)} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Does not raise ics = {f(x).diff(x).subs(x, 0): 1} classify_ode(eq, f(x), ics=ics) ########################### # f'(y) type (Derivative) # ########################### # Wrong function ics = {g(x).diff(x).subs(x, y): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Contains x ics = {f(y).diff(y).subs(y, x): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Too many args ics = {f(x, y).diff(x).subs(x, y): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Derivative wrt wrong vars ics = {Derivative(f(x), x, z).subs(x, y): 1} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # point contains f # XXX: Should be NotImplementedError ics = {f(x).diff(x).subs(x, y): f(0)} raises(ValueError, lambda: classify_ode(eq, f(x), ics=ics)) # Does not raise ics = {f(x).diff(x).subs(x, y): 1} classify_ode(eq, f(x), ics=ics) def test_classify_sysode(): # Here x is assumed to be x(t) and y as y(t) for simplicity. # Similarly diff(x,t) and diff(y,y) is assumed to be x1 and y1 respectively. k, l, m, n = symbols('k, l, m, n', Integer=True) k1, k2, k3, l1, l2, l3, m1, m2, m3 = symbols('k1, k2, k3, l1, l2, l3, m1, m2, m3', Integer=True) P, Q, R, p, q, r = symbols('P, Q, R, p, q, r', cls=Function) P1, P2, P3, Q1, Q2, R1, R2 = symbols('P1, P2, P3, Q1, Q2, R1, R2', cls=Function) x, y, z = symbols('x, y, z', cls=Function) t = symbols('t') x1 = diff(x(t),t) ; y1 = diff(y(t),t) ; z1 = diff(z(t),t) x2 = diff(x(t),t,t) ; y2 = diff(y(t),t,t) ; z2 = diff(z(t),t,t) eq1 = (Eq(diff(x(t),t), 5*t*x(t) + 2*y(t)), Eq(diff(y(t),t), 2*x(t) + 5*t*y(t))) sol1 = {'no_of_equation': 2, 'func_coeff': {(0, x(t), 0): -5*t, (1, x(t), 1): 0, (0, x(t), 1): 1, \ (1, y(t), 0): -5*t, (1, x(t), 0): -2, (0, y(t), 1): 0, (0, y(t), 0): -2, (1, y(t), 1): 1}, \ 'type_of_equation': 'type3', 'func': [x(t), y(t)], 'is_linear': True, 'eq': [-5*t*x(t) - 2*y(t) + \ Derivative(x(t), t), -5*t*y(t) - 2*x(t) + Derivative(y(t), t)], 'order': {y(t): 1, x(t): 1}} assert classify_sysode(eq1) == sol1 eq2 = (Eq(x2, k*x(t) - l*y1), Eq(y2, l*x1 + k*y(t))) sol2 = {'order': {y(t): 2, x(t): 2}, 'type_of_equation': 'type3', 'is_linear': True, 'eq': \ [-k*x(t) + l*Derivative(y(t), t) + Derivative(x(t), t, t), -k*y(t) - l*Derivative(x(t), t) + \ Derivative(y(t), t, t)], 'no_of_equation': 2, 'func_coeff': {(0, y(t), 0): 0, (0, x(t), 2): 1, \ (1, y(t), 1): 0, (1, y(t), 2): 1, (1, x(t), 2): 0, (0, y(t), 2): 0, (0, x(t), 0): -k, (1, x(t), 1): \ -l, (0, x(t), 1): 0, (0, y(t), 1): l, (1, x(t), 0): 0, (1, y(t), 0): -k}, 'func': [x(t), y(t)]} assert classify_sysode(eq2) == sol2 eq3 = (Eq(x2+4*x1+3*y1+9*x(t)+7*y(t), 11*exp(I*t)), Eq(y2+5*x1+8*y1+3*x(t)+12*y(t), 2*exp(I*t))) sol3 = {'no_of_equation': 2, 'func_coeff': {(1, x(t), 2): 0, (0, y(t), 2): 0, (0, x(t), 0): 9, \ (1, x(t), 1): 5, (0, x(t), 1): 4, (0, y(t), 1): 3, (1, x(t), 0): 3, (1, y(t), 0): 12, (0, y(t), 0): 7, \ (0, x(t), 2): 1, (1, y(t), 2): 1, (1, y(t), 1): 8}, 'type_of_equation': 'type4', 'func': [x(t), y(t)], \ 'is_linear': True, 'eq': [9*x(t) + 7*y(t) - 11*exp(I*t) + 4*Derivative(x(t), t) + 3*Derivative(y(t), t) + \ Derivative(x(t), t, t), 3*x(t) + 12*y(t) - 2*exp(I*t) + 5*Derivative(x(t), t) + 8*Derivative(y(t), t) + \ Derivative(y(t), t, t)], 'order': {y(t): 2, x(t): 2}} assert classify_sysode(eq3) == sol3 eq4 = (Eq((4*t**2 + 7*t + 1)**2*x2, 5*x(t) + 35*y(t)), Eq((4*t**2 + 7*t + 1)**2*y2, x(t) + 9*y(t))) sol4 = {'no_of_equation': 2, 'func_coeff': {(1, x(t), 2): 0, (0, y(t), 2): 0, (0, x(t), 0): -5, \ (1, x(t), 1): 0, (0, x(t), 1): 0, (0, y(t), 1): 0, (1, x(t), 0): -1, (1, y(t), 0): -9, (0, y(t), 0): -35, \ (0, x(t), 2): 16*t**4 + 56*t**3 + 57*t**2 + 14*t + 1, (1, y(t), 2): 16*t**4 + 56*t**3 + 57*t**2 + 14*t + 1, \ (1, y(t), 1): 0}, 'type_of_equation': 'type10', 'func': [x(t), y(t)], 'is_linear': True, \ 'eq': [(4*t**2 + 7*t + 1)**2*Derivative(x(t), t, t) - 5*x(t) - 35*y(t), (4*t**2 + 7*t + 1)**2*Derivative(y(t), t, t)\ - x(t) - 9*y(t)], 'order': {y(t): 2, x(t): 2}} assert classify_sysode(eq4) == sol4 eq5 = (Eq(diff(x(t),t), x(t) + y(t) + 9), Eq(diff(y(t),t), 2*x(t) + 5*y(t) + 23)) sol5 = {'no_of_equation': 2, 'func_coeff': {(0, x(t), 0): -1, (1, x(t), 1): 0, (0, x(t), 1): 1, (1, y(t), 0): -5, \ (1, x(t), 0): -2, (0, y(t), 1): 0, (0, y(t), 0): -1, (1, y(t), 1): 1}, 'type_of_equation': 'type2', \ 'func': [x(t), y(t)], 'is_linear': True, 'eq': [-x(t) - y(t) + Derivative(x(t), t) - 9, -2*x(t) - 5*y(t) + \ Derivative(y(t), t) - 23], 'order': {y(t): 1, x(t): 1}} assert classify_sysode(eq5) == sol5 eq6 = (Eq(x1, exp(k*x(t))*P(x(t),y(t))), Eq(y1,r(y(t))*P(x(t),y(t)))) sol6 = {'no_of_equation': 2, 'func_coeff': {(0, x(t), 0): 0, (1, x(t), 1): 0, (0, x(t), 1): 1, (1, y(t), 0): 0, \ (1, x(t), 0): 0, (0, y(t), 1): 0, (0, y(t), 0): 0, (1, y(t), 1): 1}, 'type_of_equation': 'type2', 'func': \ [x(t), y(t)], 'is_linear': False, 'eq': [-P(x(t), y(t))*exp(k*x(t)) + Derivative(x(t), t), -P(x(t), \ y(t))*r(y(t)) + Derivative(y(t), t)], 'order': {y(t): 1, x(t): 1}} assert classify_sysode(eq6) == sol6 eq7 = (Eq(x1, x(t)**2+y(t)/x(t)), Eq(y1, x(t)/y(t))) sol7 = {'no_of_equation': 2, 'func_coeff': {(0, x(t), 0): 0, (1, x(t), 1): 0, (0, x(t), 1): 1, (1, y(t), 0): 0, \ (1, x(t), 0): -1/y(t), (0, y(t), 1): 0, (0, y(t), 0): -1/x(t), (1, y(t), 1): 1}, 'type_of_equation': 'type3', \ 'func': [x(t), y(t)], 'is_linear': False, 'eq': [-x(t)**2 + Derivative(x(t), t) - y(t)/x(t), -x(t)/y(t) + \ Derivative(y(t), t)], 'order': {y(t): 1, x(t): 1}} assert classify_sysode(eq7) == sol7 eq8 = (Eq(x1, P1(x(t))*Q1(y(t))*R(x(t),y(t),t)), Eq(y1, P1(x(t))*Q1(y(t))*R(x(t),y(t),t))) sol8 = {'func': [x(t), y(t)], 'is_linear': False, 'type_of_equation': 'type4', 'eq': \ [-P1(x(t))*Q1(y(t))*R(x(t), y(t), t) + Derivative(x(t), t), -P1(x(t))*Q1(y(t))*R(x(t), y(t), t) + \ Derivative(y(t), t)], 'func_coeff': {(0, y(t), 1): 0, (1, y(t), 1): 1, (1, x(t), 1): 0, (0, y(t), 0): 0, \ (1, x(t), 0): 0, (0, x(t), 0): 0, (1, y(t), 0): 0, (0, x(t), 1): 1}, 'order': {y(t): 1, x(t): 1}, 'no_of_equation': 2} assert classify_sysode(eq8) == sol8 eq9 = (Eq(x1,3*y(t)-11*z(t)),Eq(y1,7*z(t)-3*x(t)),Eq(z1,11*x(t)-7*y(t))) sol9 = {'no_of_equation': 3, 'func_coeff': {(1, y(t), 0): 0, (2, y(t), 1): 0, (2, z(t), 1): 1, \ (0, x(t), 0): 0, (2, x(t), 1): 0, (1, x(t), 1): 0, (2, y(t), 0): 7, (0, x(t), 1): 1, (1, z(t), 1): 0, \ (0, y(t), 1): 0, (1, x(t), 0): 3, (0, z(t), 0): 11, (0, y(t), 0): -3, (1, z(t), 0): -7, (0, z(t), 1): 0, \ (2, x(t), 0): -11, (2, z(t), 0): 0, (1, y(t), 1): 1}, 'type_of_equation': 'type2', 'func': [x(t), y(t), z(t)], \ 'is_linear': True, 'eq': [-3*y(t) + 11*z(t) + Derivative(x(t), t), 3*x(t) - 7*z(t) + Derivative(y(t), t), \ -11*x(t) + 7*y(t) + Derivative(z(t), t)], 'order': {z(t): 1, y(t): 1, x(t): 1}} assert classify_sysode(eq9) == sol9 eq10 = (x2 + log(t)*(t*x1 - x(t)) + exp(t)*(t*y1 - y(t)), y2 + (t**2)*(t*x1 - x(t)) + (t)*(t*y1 - y(t))) sol10 = {'no_of_equation': 2, 'func_coeff': {(1, x(t), 2): 0, (0, y(t), 2): 0, (0, x(t), 0): -log(t), \ (1, x(t), 1): t**3, (0, x(t), 1): t*log(t), (0, y(t), 1): t*exp(t), (1, x(t), 0): -t**2, (1, y(t), 0): -t, \ (0, y(t), 0): -exp(t), (0, x(t), 2): 1, (1, y(t), 2): 1, (1, y(t), 1): t**2}, 'type_of_equation': 'type11', \ 'func': [x(t), y(t)], 'is_linear': True, 'eq': [(t*Derivative(x(t), t) - x(t))*log(t) + (t*Derivative(y(t), t) - \ y(t))*exp(t) + Derivative(x(t), t, t), t**2*(t*Derivative(x(t), t) - x(t)) + t*(t*Derivative(y(t), t) - y(t)) \ + Derivative(y(t), t, t)], 'order': {y(t): 2, x(t): 2}} assert classify_sysode(eq10) == sol10 eq11 = (Eq(x1,x(t)*y(t)**3), Eq(y1,y(t)**5)) sol11 = {'no_of_equation': 2, 'func_coeff': {(0, x(t), 0): -y(t)**3, (1, x(t), 1): 0, (0, x(t), 1): 1, \ (1, y(t), 0): 0, (1, x(t), 0): 0, (0, y(t), 1): 0, (0, y(t), 0): 0, (1, y(t), 1): 1}, 'type_of_equation': \ 'type1', 'func': [x(t), y(t)], 'is_linear': False, 'eq': [-x(t)*y(t)**3 + Derivative(x(t), t), \ -y(t)**5 + Derivative(y(t), t)], 'order': {y(t): 1, x(t): 1}} assert classify_sysode(eq11) == sol11 eq12 = (Eq(x1, y(t)), Eq(y1, x(t))) sol12 = {'no_of_equation': 2, 'func_coeff': {(0, x(t), 0): 0, (1, x(t), 1): 0, (0, x(t), 1): 1, (1, y(t), 0): 0, \ (1, x(t), 0): -1, (0, y(t), 1): 0, (0, y(t), 0): -1, (1, y(t), 1): 1}, 'type_of_equation': 'type1', 'func': \ [x(t), y(t)], 'is_linear': True, 'eq': [-y(t) + Derivative(x(t), t), -x(t) + Derivative(y(t), t)], 'order': {y(t): 1, x(t): 1}} assert classify_sysode(eq12) == sol12 eq13 = (Eq(x1,x(t)*y(t)*sin(t)**2), Eq(y1,y(t)**2*sin(t)**2)) sol13 = {'no_of_equation': 2, 'func_coeff': {(0, x(t), 0): -y(t)*sin(t)**2, (1, x(t), 1): 0, (0, x(t), 1): 1, \ (1, y(t), 0): 0, (1, x(t), 0): 0, (0, y(t), 1): 0, (0, y(t), 0): -x(t)*sin(t)**2, (1, y(t), 1): 1}, \ 'type_of_equation': 'type4', 'func': [x(t), y(t)], 'is_linear': False, 'eq': [-x(t)*y(t)*sin(t)**2 + \ Derivative(x(t), t), -y(t)**2*sin(t)**2 + Derivative(y(t), t)], 'order': {y(t): 1, x(t): 1}} assert classify_sysode(eq13) == sol13 eq14 = (Eq(x1, 21*x(t)), Eq(y1, 17*x(t)+3*y(t)), Eq(z1, 5*x(t)+7*y(t)+9*z(t))) sol14 = {'no_of_equation': 3, 'func_coeff': {(1, y(t), 0): -3, (2, y(t), 1): 0, (2, z(t), 1): 1, \ (0, x(t), 0): -21, (2, x(t), 1): 0, (1, x(t), 1): 0, (2, y(t), 0): -7, (0, x(t), 1): 1, (1, z(t), 1): 0, \ (0, y(t), 1): 0, (1, x(t), 0): -17, (0, z(t), 0): 0, (0, y(t), 0): 0, (1, z(t), 0): 0, (0, z(t), 1): 0, \ (2, x(t), 0): -5, (2, z(t), 0): -9, (1, y(t), 1): 1}, 'type_of_equation': 'type1', 'func': [x(t), y(t), z(t)], \ 'is_linear': True, 'eq': [-21*x(t) + Derivative(x(t), t), -17*x(t) - 3*y(t) + Derivative(y(t), t), -5*x(t) - \ 7*y(t) - 9*z(t) + Derivative(z(t), t)], 'order': {z(t): 1, y(t): 1, x(t): 1}} assert classify_sysode(eq14) == sol14 eq15 = (Eq(x1,4*x(t)+5*y(t)+2*z(t)),Eq(y1,x(t)+13*y(t)+9*z(t)),Eq(z1,32*x(t)+41*y(t)+11*z(t))) sol15 = {'no_of_equation': 3, 'func_coeff': {(1, y(t), 0): -13, (2, y(t), 1): 0, (2, z(t), 1): 1, \ (0, x(t), 0): -4, (2, x(t), 1): 0, (1, x(t), 1): 0, (2, y(t), 0): -41, (0, x(t), 1): 1, (1, z(t), 1): 0, \ (0, y(t), 1): 0, (1, x(t), 0): -1, (0, z(t), 0): -2, (0, y(t), 0): -5, (1, z(t), 0): -9, (0, z(t), 1): 0, \ (2, x(t), 0): -32, (2, z(t), 0): -11, (1, y(t), 1): 1}, 'type_of_equation': 'type6', 'func': \ [x(t), y(t), z(t)], 'is_linear': True, 'eq': [-4*x(t) - 5*y(t) - 2*z(t) + Derivative(x(t), t), -x(t) - 13*y(t) - \ 9*z(t) + Derivative(y(t), t), -32*x(t) - 41*y(t) - 11*z(t) + Derivative(z(t), t)], 'order': {z(t): 1, y(t): 1, x(t): 1}} assert classify_sysode(eq15) == sol15 eq16 = (Eq(3*x1,4*5*(y(t)-z(t))),Eq(4*y1,3*5*(z(t)-x(t))),Eq(5*z1,3*4*(x(t)-y(t)))) sol16 = {'no_of_equation': 3, 'func_coeff': {(1, y(t), 0): 0, (2, y(t), 1): 0, (2, z(t), 1): 5, \ (0, x(t), 0): 0, (2, x(t), 1): 0, (1, x(t), 1): 0, (2, y(t), 0): 12, (0, x(t), 1): 3, (1, z(t), 1): 0, \ (0, y(t), 1): 0, (1, x(t), 0): 15, (0, z(t), 0): 20, (0, y(t), 0): -20, (1, z(t), 0): -15, (0, z(t), 1): 0, \ (2, x(t), 0): -12, (2, z(t), 0): 0, (1, y(t), 1): 4}, 'type_of_equation': 'type3', 'func': [x(t), y(t), z(t)], \ 'is_linear': True, 'eq': [-20*y(t) + 20*z(t) + 3*Derivative(x(t), t), 15*x(t) - 15*z(t) + 4*Derivative(y(t), t), \ -12*x(t) + 12*y(t) + 5*Derivative(z(t), t)], 'order': {z(t): 1, y(t): 1, x(t): 1}} assert classify_sysode(eq16) == sol16 # issue 8193: funcs parameter for classify_sysode has to actually work assert classify_sysode(eq1, funcs=[x(t), y(t)]) == sol1 def test_solve_ics(): # Basic tests that things work from dsolve. assert dsolve(f(x).diff(x) - 1/f(x), f(x), ics={f(1): 2}) == \ Eq(f(x), sqrt(2 * x + 2)) assert dsolve(f(x).diff(x) - f(x), f(x), ics={f(0): 1}) == Eq(f(x), exp(x)) assert dsolve(f(x).diff(x) - f(x), f(x), ics={f(x).diff(x).subs(x, 0): 1}) == Eq(f(x), exp(x)) assert dsolve(f(x).diff(x, x) + f(x), f(x), ics={f(0): 1, f(x).diff(x).subs(x, 0): 1}) == Eq(f(x), sin(x) + cos(x)) assert dsolve([f(x).diff(x) - f(x) + g(x), g(x).diff(x) - g(x) - f(x)], [f(x), g(x)], ics={f(0): 1, g(0): 0}) == [Eq(f(x), exp(x)*cos(x)), Eq(g(x), exp(x)*sin(x))] # Test cases where dsolve returns two solutions. eq = (x**2*f(x)**2 - x).diff(x) assert dsolve(eq, f(x), ics={f(1): 0}) == [Eq(f(x), -sqrt(x - 1)/x), Eq(f(x), sqrt(x - 1)/x)] assert dsolve(eq, f(x), ics={f(x).diff(x).subs(x, 1): 0}) == [Eq(f(x), -sqrt(x - S(1)/2)/x), Eq(f(x), sqrt(x - S(1)/2)/x)] eq = cos(f(x)) - (x*sin(f(x)) - f(x)**2)*f(x).diff(x) assert dsolve(eq, f(x), ics={f(0):1}, hint='1st_exact', simplify=False) == Eq(x*cos(f(x)) + f(x)**3/3, S(1)/3) assert dsolve(eq, f(x), ics={f(0):1}, hint='1st_exact', simplify=True) == Eq(x*cos(f(x)) + f(x)**3/3, S(1)/3) assert solve_ics([Eq(f(x), C1*exp(x))], [f(x)], [C1], {f(0): 1}) == {C1: 1} assert solve_ics([Eq(f(x), C1*sin(x) + C2*cos(x))], [f(x)], [C1, C2], {f(0): 1, f(pi/2): 1}) == {C1: 1, C2: 1} assert solve_ics([Eq(f(x), C1*sin(x) + C2*cos(x))], [f(x)], [C1, C2], {f(0): 1, f(x).diff(x).subs(x, 0): 1}) == {C1: 1, C2: 1} assert solve_ics([Eq(f(x), C1*sin(x) + C2*cos(x))], [f(x)], [C1, C2], {f(0): 1}) == \ {C2: 1} # Some more complicated tests Refer to PR #16098 assert dsolve(f(x).diff(x)*(f(x).diff(x, 2)-x), ics={f(0):0, f(x).diff(x).subs(x, 1):0}) == \ [Eq(f(x), 0), Eq(f(x), x ** 3 / 6 - x / 2)] assert dsolve(f(x).diff(x)*(f(x).diff(x, 2)-x), ics={f(0):0}) == \ [Eq(f(x), 0), Eq(f(x), C2*x + x**3/6)] K, r, f0 = symbols('K r f0') sol = Eq(f(x), -K*f0*exp(r*x)/((K - f0)*(-f0*exp(r*x)/(K - f0) - 1))) assert (dsolve(Eq(f(x).diff(x), r * f(x) * (1 - f(x) / K)), f(x), ics={f(0): f0})) == sol #Order dependent issues Refer to PR #16098 assert dsolve(f(x).diff(x)*(f(x).diff(x, 2)-x), ics={f(x).diff(x).subs(x,0):0, f(0):0}) == \ [Eq(f(x), 0), Eq(f(x), x ** 3 / 6)] assert dsolve(f(x).diff(x)*(f(x).diff(x, 2)-x), ics={f(0):0, f(x).diff(x).subs(x,0):0}) == \ [Eq(f(x), 0), Eq(f(x), x ** 3 / 6)] # XXX: Ought to be ValueError raises(ValueError, lambda: solve_ics([Eq(f(x), C1*sin(x) + C2*cos(x))], [f(x)], [C1, C2], {f(0): 1, f(pi): 1})) # Degenerate case. f'(0) is identically 0. raises(ValueError, lambda: solve_ics([Eq(f(x), sqrt(C1 - x**2))], [f(x)], [C1], {f(x).diff(x).subs(x, 0): 0})) EI, q, L = symbols('EI q L') # eq = Eq(EI*diff(f(x), x, 4), q) sols = [Eq(f(x), C1 + C2*x + C3*x**2 + C4*x**3 + q*x**4/(24*EI))] funcs = [f(x)] constants = [C1, C2, C3, C4] # Test both cases, Derivative (the default from f(x).diff(x).subs(x, L)), # and Subs ics1 = {f(0): 0, f(x).diff(x).subs(x, 0): 0, f(L).diff(L, 2): 0, f(L).diff(L, 3): 0} ics2 = {f(0): 0, f(x).diff(x).subs(x, 0): 0, Subs(f(x).diff(x, 2), x, L): 0, Subs(f(x).diff(x, 3), x, L): 0} solved_constants1 = solve_ics(sols, funcs, constants, ics1) solved_constants2 = solve_ics(sols, funcs, constants, ics2) assert solved_constants1 == solved_constants2 == { C1: 0, C2: 0, C3: L**2*q/(4*EI), C4: -L*q/(6*EI)} def test_ode_order(): f = Function('f') g = Function('g') x = Symbol('x') assert ode_order(3*x*exp(f(x)), f(x)) == 0 assert ode_order(x*diff(f(x), x) + 3*x*f(x) - sin(x)/x, f(x)) == 1 assert ode_order(x**2*f(x).diff(x, x) + x*diff(f(x), x) - f(x), f(x)) == 2 assert ode_order(diff(x*exp(f(x)), x, x), f(x)) == 2 assert ode_order(diff(x*diff(x*exp(f(x)), x, x), x), f(x)) == 3 assert ode_order(diff(f(x), x, x), g(x)) == 0 assert ode_order(diff(f(x), x, x)*diff(g(x), x), f(x)) == 2 assert ode_order(diff(f(x), x, x)*diff(g(x), x), g(x)) == 1 assert ode_order(diff(x*diff(x*exp(f(x)), x, x), x), g(x)) == 0 # issue 5835: ode_order has to also work for unevaluated derivatives # (ie, without using doit()). assert ode_order(Derivative(x*f(x), x), f(x)) == 1 assert ode_order(x*sin(Derivative(x*f(x)**2, x, x)), f(x)) == 2 assert ode_order(Derivative(x*Derivative(x*exp(f(x)), x, x), x), g(x)) == 0 assert ode_order(Derivative(f(x), x, x), g(x)) == 0 assert ode_order(Derivative(x*exp(f(x)), x, x), f(x)) == 2 assert ode_order(Derivative(f(x), x, x)*Derivative(g(x), x), g(x)) == 1 assert ode_order(Derivative(x*Derivative(f(x), x, x), x), f(x)) == 3 assert ode_order( x*sin(Derivative(x*Derivative(f(x), x)**2, x, x)), f(x)) == 3 # In all tests below, checkodesol has the order option set to prevent # superfluous calls to ode_order(), and the solve_for_func flag set to False # because dsolve() already tries to solve for the function, unless the # simplify=False option is set. def test_old_ode_tests(): # These are simple tests from the old ode module eq1 = Eq(f(x).diff(x), 0) eq2 = Eq(3*f(x).diff(x) - 5, 0) eq3 = Eq(3*f(x).diff(x), 5) eq4 = Eq(9*f(x).diff(x, x) + f(x), 0) eq5 = Eq(9*f(x).diff(x, x), f(x)) # Type: a(x)f'(x)+b(x)*f(x)+c(x)=0 eq6 = Eq(x**2*f(x).diff(x) + 3*x*f(x) - sin(x)/x, 0) eq7 = Eq(f(x).diff(x, x) - 3*diff(f(x), x) + 2*f(x), 0) # Type: 2nd order, constant coefficients (two real different roots) eq8 = Eq(f(x).diff(x, x) - 4*diff(f(x), x) + 4*f(x), 0) # Type: 2nd order, constant coefficients (two real equal roots) eq9 = Eq(f(x).diff(x, x) + 2*diff(f(x), x) + 3*f(x), 0) # Type: 2nd order, constant coefficients (two complex roots) eq10 = Eq(3*f(x).diff(x) - 1, 0) eq11 = Eq(x*f(x).diff(x) - 1, 0) sol1 = Eq(f(x), C1) sol2 = Eq(f(x), C1 + 5*x/3) sol3 = Eq(f(x), C1 + 5*x/3) sol4 = Eq(f(x), C1*sin(x/3) + C2*cos(x/3)) sol5 = Eq(f(x), C1*exp(-x/3) + C2*exp(x/3)) sol6 = Eq(f(x), (C1 - cos(x))/x**3) sol7 = Eq(f(x), (C1 + C2*exp(x))*exp(x)) sol8 = Eq(f(x), (C1 + C2*x)*exp(2*x)) sol9 = Eq(f(x), (C1*sin(x*sqrt(2)) + C2*cos(x*sqrt(2)))*exp(-x)) sol10 = Eq(f(x), C1 + x/3) sol11 = Eq(f(x), C1 + log(x)) assert dsolve(eq1) == sol1 assert dsolve(eq1.lhs) == sol1 assert dsolve(eq2) == sol2 assert dsolve(eq3) == sol3 assert dsolve(eq4) == sol4 assert dsolve(eq5) == sol5 assert dsolve(eq6) == sol6 assert dsolve(eq7) == sol7 assert dsolve(eq8) == sol8 assert dsolve(eq9) == sol9 assert dsolve(eq10) == sol10 assert dsolve(eq11) == sol11 assert checkodesol(eq1, sol1, order=1, solve_for_func=False)[0] assert checkodesol(eq2, sol2, order=1, solve_for_func=False)[0] assert checkodesol(eq3, sol3, order=1, solve_for_func=False)[0] assert checkodesol(eq4, sol4, order=2, solve_for_func=False)[0] assert checkodesol(eq5, sol5, order=2, solve_for_func=False)[0] assert checkodesol(eq6, sol6, order=1, solve_for_func=False)[0] assert checkodesol(eq7, sol7, order=2, solve_for_func=False)[0] assert checkodesol(eq8, sol8, order=2, solve_for_func=False)[0] assert checkodesol(eq9, sol9, order=2, solve_for_func=False)[0] assert checkodesol(eq10, sol10, order=1, solve_for_func=False)[0] assert checkodesol(eq11, sol11, order=1, solve_for_func=False)[0] def test_1st_linear(): # Type: first order linear form f'(x)+p(x)f(x)=q(x) eq = Eq(f(x).diff(x) + x*f(x), x**2) sol = Eq(f(x), (C1 + x*exp(x**2/2) - sqrt(2)*sqrt(pi)*erfi(sqrt(2)*x/2)/2)*exp(-x**2/2)) assert dsolve(eq, hint='1st_linear') == sol assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] def test_Bernoulli(): # Type: Bernoulli, f'(x) + p(x)*f(x) == q(x)*f(x)**n eq = Eq(x*f(x).diff(x) + f(x) - f(x)**2, 0) sol = dsolve(eq, f(x), hint='Bernoulli') assert sol == Eq(f(x), 1/(x*(C1 + 1/x))) assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] def test_Riccati_special_minus2(): # Type: Riccati special alpha = -2, a*dy/dx + b*y**2 + c*y/x +d/x**2 eq = 2*f(x).diff(x) + f(x)**2 - f(x)/x + 3*x**(-2) sol = dsolve(eq, f(x), hint='Riccati_special_minus2') assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] @slow def test_1st_exact1(): # Type: Exact differential equation, p(x,f) + q(x,f)*f' == 0, # where dp/df == dq/dx eq1 = sin(x)*cos(f(x)) + cos(x)*sin(f(x))*f(x).diff(x) eq2 = (2*x*f(x) + 1)/f(x) + (f(x) - x)/f(x)**2*f(x).diff(x) eq3 = 2*x + f(x)*cos(x) + (2*f(x) + sin(x) - sin(f(x)))*f(x).diff(x) eq4 = cos(f(x)) - (x*sin(f(x)) - f(x)**2)*f(x).diff(x) eq5 = 2*x*f(x) + (x**2 + f(x)**2)*f(x).diff(x) sol1 = [Eq(f(x), -acos(C1/cos(x)) + 2*pi), Eq(f(x), acos(C1/cos(x)))] sol2 = Eq(f(x), exp(C1 - x**2 + LambertW(-x*exp(-C1 + x**2)))) sol2b = Eq(log(f(x)) + x/f(x) + x**2, C1) sol3 = Eq(f(x)*sin(x) + cos(f(x)) + x**2 + f(x)**2, C1) sol4 = Eq(x*cos(f(x)) + f(x)**3/3, C1) sol5 = Eq(x**2*f(x) + f(x)**3/3, C1) assert dsolve(eq1, f(x), hint='1st_exact') == sol1 assert dsolve(eq2, f(x), hint='1st_exact') == sol2 assert dsolve(eq3, f(x), hint='1st_exact') == sol3 assert dsolve(eq4, hint='1st_exact') == sol4 assert dsolve(eq5, hint='1st_exact', simplify=False) == sol5 assert checkodesol(eq1, sol1, order=1, solve_for_func=False)[0] # issue 5080 blocks the testing of this solution # FIXME: assert checkodesol(eq2, sol2, order=1, solve_for_func=False)[0] assert checkodesol(eq2, sol2b, order=1, solve_for_func=False)[0] assert checkodesol(eq3, sol3, order=1, solve_for_func=False)[0] assert checkodesol(eq4, sol4, order=1, solve_for_func=False)[0] assert checkodesol(eq5, sol5, order=1, solve_for_func=False)[0] @slow @XFAIL def test_1st_exact2(): """ This is an exact equation that fails under the exact engine. It is caught by first order homogeneous albeit with a much contorted solution. The exact engine fails because of a poorly simplified integral of q(0,y)dy, where q is the function multiplying f'. The solutions should be Eq(sqrt(x**2+f(x)**2)**3+y**3, C1). The equation below is equivalent, but it is so complex that checkodesol fails, and takes a long time to do so. """ if ON_TRAVIS: skip("Too slow for travis.") eq = (x*sqrt(x**2 + f(x)**2) - (x**2*f(x)/(f(x) - sqrt(x**2 + f(x)**2)))*f(x).diff(x)) sol = dsolve(eq) assert sol == Eq(log(x), C1 - 9*sqrt(1 + f(x)**2/x**2)*asinh(f(x)/x)/(-27*f(x)/x + 27*sqrt(1 + f(x)**2/x**2)) - 9*sqrt(1 + f(x)**2/x**2)* log(1 - sqrt(1 + f(x)**2/x**2)*f(x)/x + 2*f(x)**2/x**2)/ (-27*f(x)/x + 27*sqrt(1 + f(x)**2/x**2)) + 9*asinh(f(x)/x)*f(x)/(x*(-27*f(x)/x + 27*sqrt(1 + f(x)**2/x**2))) + 9*f(x)*log(1 - sqrt(1 + f(x)**2/x**2)*f(x)/x + 2*f(x)**2/x**2)/ (x*(-27*f(x)/x + 27*sqrt(1 + f(x)**2/x**2)))) assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] def test_separable1(): # test_separable1-5 are from Ordinary Differential Equations, Tenenbaum and # Pollard, pg. 55 eq1 = f(x).diff(x) - f(x) eq2 = x*f(x).diff(x) - f(x) eq3 = f(x).diff(x) + sin(x) eq4 = f(x)**2 + 1 - (x**2 + 1)*f(x).diff(x) eq5 = f(x).diff(x)/tan(x) - f(x) - 2 eq6 = f(x).diff(x) * (1 - sin(f(x))) - 1 sol1 = Eq(f(x), C1*exp(x)) sol2 = Eq(f(x), C1*x) sol3 = Eq(f(x), C1 + cos(x)) sol4 = Eq(f(x), tan(C1 + atan(x))) sol5 = Eq(f(x), C1/cos(x) - 2) sol6 = Eq(-x + f(x) + cos(f(x)), C1) assert dsolve(eq1, hint='separable') == sol1 assert dsolve(eq2, hint='separable') == sol2 assert dsolve(eq3, hint='separable') == sol3 assert dsolve(eq4, hint='separable') == sol4 assert dsolve(eq5, hint='separable') == sol5 assert dsolve(eq6, hint='separable') == sol6 assert checkodesol(eq1, sol1, order=1, solve_for_func=False)[0] assert checkodesol(eq2, sol2, order=1, solve_for_func=False)[0] assert checkodesol(eq3, sol3, order=1, solve_for_func=False)[0] assert checkodesol(eq4, sol4, order=1, solve_for_func=False)[0] assert checkodesol(eq5, sol5, order=1, solve_for_func=False)[0] assert checkodesol(eq6, sol6, order=1, solve_for_func=False)[0] @slow def test_separable2(): a = Symbol('a') eq6 = f(x)*x**2*f(x).diff(x) - f(x)**3 - 2*x**2*f(x).diff(x) eq7 = f(x)**2 - 1 - (2*f(x) + x*f(x))*f(x).diff(x) eq8 = x*log(x)*f(x).diff(x) + sqrt(1 + f(x)**2) eq9 = exp(x + 1)*tan(f(x)) + cos(f(x))*f(x).diff(x) eq10 = (x*cos(f(x)) + x**2*sin(f(x))*f(x).diff(x) - a**2*sin(f(x))*f(x).diff(x)) sol6 = Eq(Integral((u - 2)/u**3, (u, f(x))), C1 + Integral(x**(-2), x)) sol7 = Eq(-log(-1 + f(x)**2)/2, C1 - log(2 + x)) sol8 = Eq(asinh(f(x)), C1 - log(log(x))) # integrate cannot handle the integral on the lhs (cos/tan) sol9 = Eq(Integral(cos(u)/tan(u), (u, f(x))), C1 + Integral(-exp(1)*exp(x), x)) sol10 = Eq(-log(cos(f(x))), C1 - log(- a**2 + x**2)/2) assert dsolve(eq6, hint='separable_Integral').dummy_eq(sol6) assert dsolve(eq7, hint='separable', simplify=False) == sol7 assert dsolve(eq8, hint='separable', simplify=False) == sol8 assert dsolve(eq9, hint='separable_Integral').dummy_eq(sol9) assert dsolve(eq10, hint='separable', simplify=False) == sol10 assert checkodesol(eq6, sol6, order=1, solve_for_func=False)[0] assert checkodesol(eq7, sol7, order=1, solve_for_func=False)[0] assert checkodesol(eq8, sol8, order=1, solve_for_func=False)[0] assert checkodesol(eq9, sol9, order=1, solve_for_func=False)[0] assert checkodesol(eq10, sol10, order=1, solve_for_func=False)[0] def test_separable3(): eq11 = f(x).diff(x) - f(x)*tan(x) eq12 = (x - 1)*cos(f(x))*f(x).diff(x) - 2*x*sin(f(x)) eq13 = f(x).diff(x) - f(x)*log(f(x))/tan(x) sol11 = Eq(f(x), C1/cos(x)) sol12 = Eq(log(sin(f(x))), C1 + 2*x + 2*log(x - 1)) sol13 = Eq(log(log(f(x))), C1 + log(sin(x))) assert dsolve(eq11, hint='separable') == sol11 assert dsolve(eq12, hint='separable', simplify=False) == sol12 assert dsolve(eq13, hint='separable', simplify=False) == sol13 assert checkodesol(eq11, sol11, order=1, solve_for_func=False)[0] assert checkodesol(eq12, sol12, order=1, solve_for_func=False)[0] assert checkodesol(eq13, sol13, order=1, solve_for_func=False)[0] def test_separable4(): # This has a slow integral (1/((1 + y**2)*atan(y))), so we isolate it. eq14 = x*f(x).diff(x) + (1 + f(x)**2)*atan(f(x)) sol14 = Eq(log(atan(f(x))), C1 - log(x)) assert dsolve(eq14, hint='separable', simplify=False) == sol14 assert checkodesol(eq14, sol14, order=1, solve_for_func=False)[0] def test_separable5(): eq15 = f(x).diff(x) + x*(f(x) + 1) eq16 = exp(f(x)**2)*(x**2 + 2*x + 1) + (x*f(x) + f(x))*f(x).diff(x) eq17 = f(x).diff(x) + f(x) eq18 = sin(x)*cos(2*f(x)) + cos(x)*sin(2*f(x))*f(x).diff(x) eq19 = (1 - x)*f(x).diff(x) - x*(f(x) + 1) eq20 = f(x)*diff(f(x), x) + x - 3*x*f(x)**2 eq21 = f(x).diff(x) - exp(x + f(x)) sol15 = Eq(f(x), -1 + C1*exp(-x**2/2)) sol16 = Eq(-exp(-f(x)**2)/2, C1 - x - x**2/2) sol17 = Eq(f(x), C1*exp(-x)) sol18 = Eq(-log(cos(2*f(x)))/2, C1 + log(cos(x))) sol19 = Eq(f(x), (C1*exp(-x) - x + 1)/(x - 1)) sol20 = Eq(log(-1 + 3*f(x)**2)/6, C1 + x**2/2) sol21 = Eq(-exp(-f(x)), C1 + exp(x)) assert dsolve(eq15, hint='separable') == sol15 assert dsolve(eq16, hint='separable', simplify=False) == sol16 assert dsolve(eq17, hint='separable') == sol17 assert dsolve(eq18, hint='separable', simplify=False) == sol18 assert dsolve(eq19, hint='separable') == sol19 assert dsolve(eq20, hint='separable', simplify=False) == sol20 assert dsolve(eq21, hint='separable', simplify=False) == sol21 assert checkodesol(eq15, sol15, order=1, solve_for_func=False)[0] assert checkodesol(eq16, sol16, order=1, solve_for_func=False)[0] assert checkodesol(eq17, sol17, order=1, solve_for_func=False)[0] assert checkodesol(eq18, sol18, order=1, solve_for_func=False)[0] assert checkodesol(eq19, sol19, order=1, solve_for_func=False)[0] assert checkodesol(eq20, sol20, order=1, solve_for_func=False)[0] assert checkodesol(eq21, sol21, order=1, solve_for_func=False)[0] def test_separable_1_5_checkodesol(): eq12 = (x - 1)*cos(f(x))*f(x).diff(x) - 2*x*sin(f(x)) sol12 = Eq(-log(1 - cos(f(x))**2)/2, C1 - 2*x - 2*log(1 - x)) assert checkodesol(eq12, sol12, order=1, solve_for_func=False)[0] def test_homogeneous_order(): assert homogeneous_order(exp(y/x) + tan(y/x), x, y) == 0 assert homogeneous_order(x**2 + sin(x)*cos(y), x, y) is None assert homogeneous_order(x - y - x*sin(y/x), x, y) == 1 assert homogeneous_order((x*y + sqrt(x**4 + y**4) + x**2*(log(x) - log(y)))/ (pi*x**Rational(2, 3)*sqrt(y)**3), x, y) == Rational(-1, 6) assert homogeneous_order(y/x*cos(y/x) - x/y*sin(y/x) + cos(y/x), x, y) == 0 assert homogeneous_order(f(x), x, f(x)) == 1 assert homogeneous_order(f(x)**2, x, f(x)) == 2 assert homogeneous_order(x*y*z, x, y) == 2 assert homogeneous_order(x*y*z, x, y, z) == 3 assert homogeneous_order(x**2*f(x)/sqrt(x**2 + f(x)**2), f(x)) is None assert homogeneous_order(f(x, y)**2, x, f(x, y), y) == 2 assert homogeneous_order(f(x, y)**2, x, f(x), y) is None assert homogeneous_order(f(x, y)**2, x, f(x, y)) is None assert homogeneous_order(f(y, x)**2, x, y, f(x, y)) is None assert homogeneous_order(f(y), f(x), x) is None assert homogeneous_order(-f(x)/x + 1/sin(f(x)/ x), f(x), x) == 0 assert homogeneous_order(log(1/y) + log(x**2), x, y) is None assert homogeneous_order(log(1/y) + log(x), x, y) == 0 assert homogeneous_order(log(x/y), x, y) == 0 assert homogeneous_order(2*log(1/y) + 2*log(x), x, y) == 0 a = Symbol('a') assert homogeneous_order(a*log(1/y) + a*log(x), x, y) == 0 assert homogeneous_order(f(x).diff(x), x, y) is None assert homogeneous_order(-f(x).diff(x) + x, x, y) is None assert homogeneous_order(O(x), x, y) is None assert homogeneous_order(x + O(x**2), x, y) is None assert homogeneous_order(x**pi, x) == pi assert homogeneous_order(x**x, x) is None raises(ValueError, lambda: homogeneous_order(x*y)) @slow def test_1st_homogeneous_coeff_ode(): # Type: First order homogeneous, y'=f(y/x) eq1 = f(x)/x*cos(f(x)/x) - (x/f(x)*sin(f(x)/x) + cos(f(x)/x))*f(x).diff(x) eq2 = x*f(x).diff(x) - f(x) - x*sin(f(x)/x) eq3 = f(x) + (x*log(f(x)/x) - 2*x)*diff(f(x), x) eq4 = 2*f(x)*exp(x/f(x)) + f(x)*f(x).diff(x) - 2*x*exp(x/f(x))*f(x).diff(x) eq5 = 2*x**2*f(x) + f(x)**3 + (x*f(x)**2 - 2*x**3)*f(x).diff(x) eq6 = x*exp(f(x)/x) - f(x)*sin(f(x)/x) + x*sin(f(x)/x)*f(x).diff(x) eq7 = (x + sqrt(f(x)**2 - x*f(x)))*f(x).diff(x) - f(x) eq8 = x + f(x) - (x - f(x))*f(x).diff(x) sol1 = Eq(log(x), C1 - log(f(x)*sin(f(x)/x)/x)) sol2 = Eq(log(x), log(C1) + log(cos(f(x)/x) - 1)/2 - log(cos(f(x)/x) + 1)/2) sol3 = Eq(f(x), -exp(C1)*LambertW(-x*exp(-C1 + 1))) sol4 = Eq(log(f(x)), C1 - 2*exp(x/f(x))) sol5 = Eq(f(x), exp(2*C1 + LambertW(-2*x**4*exp(-4*C1))/2)/x) sol6 = Eq(log(x), C1 + exp(-f(x)/x)*sin(f(x)/x)/2 + exp(-f(x)/x)*cos(f(x)/x)/2) sol7 = Eq(log(f(x)), C1 - 2*sqrt(-x/f(x) + 1)) sol8 = Eq(log(x), C1 - log(sqrt(1 + f(x)**2/x**2)) + atan(f(x)/x)) # indep_div_dep actually has a simpler solution for eq2, # but it runs too slow assert dsolve(eq1, hint='1st_homogeneous_coeff_subs_dep_div_indep') == sol1 assert dsolve(eq2, hint='1st_homogeneous_coeff_subs_dep_div_indep', simplify=False) == sol2 assert dsolve(eq3, hint='1st_homogeneous_coeff_best') == sol3 assert dsolve(eq4, hint='1st_homogeneous_coeff_best') == sol4 assert dsolve(eq5, hint='1st_homogeneous_coeff_best') == sol5 assert dsolve(eq6, hint='1st_homogeneous_coeff_subs_dep_div_indep') == sol6 assert dsolve(eq7, hint='1st_homogeneous_coeff_best') == sol7 assert dsolve(eq8, hint='1st_homogeneous_coeff_best') == sol8 # FIXME: sol3 and sol5 don't work with checkodesol (because of LambertW?) # previous code was testing with these other solutions: sol3b = Eq(-f(x)/(1 + log(x/f(x))), C1) sol5b = Eq(log(C1*x*sqrt(1/x)*sqrt(f(x))) + x**2/(2*f(x)**2), 0) assert checkodesol(eq1, sol1, order=1, solve_for_func=False)[0] assert checkodesol(eq2, sol2, order=1, solve_for_func=False)[0] assert checkodesol(eq3, sol3b, order=1, solve_for_func=False)[0] assert checkodesol(eq4, sol4, order=1, solve_for_func=False)[0] assert checkodesol(eq5, sol5b, order=1, solve_for_func=False)[0] assert checkodesol(eq6, sol6, order=1, solve_for_func=False)[0] assert checkodesol(eq8, sol8, order=1, solve_for_func=False)[0] def test_1st_homogeneous_coeff_ode_check2(): eq2 = x*f(x).diff(x) - f(x) - x*sin(f(x)/x) sol2 = Eq(x/tan(f(x)/(2*x)), C1) assert checkodesol(eq2, sol2, order=1, solve_for_func=False)[0] @XFAIL def test_1st_homogeneous_coeff_ode_check3(): skip('This is a known issue.') # checker cannot determine that the following expression is zero: # (False, # x*(log(exp(-LambertW(C1*x))) + # LambertW(C1*x))*exp(-LambertW(C1*x) + 1)) # This is blocked by issue 5080. eq3 = f(x) + (x*log(f(x)/x) - 2*x)*diff(f(x), x) sol3a = Eq(f(x), x*exp(1 - LambertW(C1*x))) assert checkodesol(eq3, sol3a, solve_for_func=True)[0] # Checker can't verify this form either # (False, # C1*(log(C1*LambertW(C2*x)/x) + LambertW(C2*x) - 1)*LambertW(C2*x)) # It is because a = W(a)*exp(W(a)), so log(a) == log(W(a)) + W(a) and C2 = # -E/C1 (which can be verified by solving with simplify=False). sol3b = Eq(f(x), C1*LambertW(C2*x)) assert checkodesol(eq3, sol3b, solve_for_func=True)[0] def test_1st_homogeneous_coeff_ode_check7(): eq7 = (x + sqrt(f(x)**2 - x*f(x)))*f(x).diff(x) - f(x) sol7 = Eq(log(C1*f(x)) + 2*sqrt(1 - x/f(x)), 0) assert checkodesol(eq7, sol7, order=1, solve_for_func=False)[0] def test_1st_homogeneous_coeff_ode2(): eq1 = f(x).diff(x) - f(x)/x + 1/sin(f(x)/x) eq2 = x**2 + f(x)**2 - 2*x*f(x)*f(x).diff(x) eq3 = x*exp(f(x)/x) + f(x) - x*f(x).diff(x) sol1 = [Eq(f(x), x*(-acos(C1 + log(x)) + 2*pi)), Eq(f(x), x*acos(C1 + log(x)))] sol2 = Eq(log(f(x)), log(C1) + log(x/f(x)) - log(x**2/f(x)**2 - 1)) sol3 = Eq(f(x), log((1/(C1 - log(x)))**x)) # specific hints are applied for speed reasons assert dsolve(eq1, hint='1st_homogeneous_coeff_subs_dep_div_indep') == sol1 assert dsolve(eq2, hint='1st_homogeneous_coeff_best', simplify=False) == sol2 assert dsolve(eq3, hint='1st_homogeneous_coeff_subs_dep_div_indep') == sol3 # FIXME: sol3 doesn't work with checkodesol (because of **x?) # previous code was testing with this other solution: sol3b = Eq(f(x), log(log(C1/x)**(-x))) assert checkodesol(eq1, sol1, order=1, solve_for_func=False)[0] assert checkodesol(eq2, sol2, order=1, solve_for_func=False)[0] assert checkodesol(eq3, sol3b, order=1, solve_for_func=False)[0] def test_1st_homogeneous_coeff_ode_check9(): _u2 = Dummy('u2') __a = Dummy('a') eq9 = f(x)**2 + (x*sqrt(f(x)**2 - x**2) - x*f(x))*f(x).diff(x) sol9 = Eq(-Integral(-1/(-(1 - sqrt(1 - _u2**2))*_u2 + _u2), (_u2, __a, x/f(x))) + log(C1*f(x)), 0) assert checkodesol(eq9, sol9, order=1, solve_for_func=False)[0] def test_1st_homogeneous_coeff_ode3(): # The standard integration engine cannot handle one of the integrals # involved (see issue 4551). meijerg code comes up with an answer, but in # unconventional form. # checkodesol fails for this equation, so its test is in # test_1st_homogeneous_coeff_ode_check9 above. It has to compare string # expressions because u2 is a dummy variable. eq = f(x)**2 + (x*sqrt(f(x)**2 - x**2) - x*f(x))*f(x).diff(x) sol = Eq(log(f(x)), C1 + Piecewise( (acosh(f(x)/x), abs(f(x)**2)/x**2 > 1), (-I*asin(f(x)/x), True))) assert dsolve(eq, hint='1st_homogeneous_coeff_subs_indep_div_dep') == sol def test_1st_homogeneous_coeff_corner_case(): eq1 = f(x).diff(x) - f(x)/x c1 = classify_ode(eq1, f(x)) eq2 = x*f(x).diff(x) - f(x) c2 = classify_ode(eq2, f(x)) sdi = "1st_homogeneous_coeff_subs_dep_div_indep" sid = "1st_homogeneous_coeff_subs_indep_div_dep" assert sid not in c1 and sdi not in c1 assert sid not in c2 and sdi not in c2 @slow def test_nth_linear_constant_coeff_homogeneous(): # From Exercise 20, in Ordinary Differential Equations, # Tenenbaum and Pollard, pg. 220 a = Symbol('a', positive=True) k = Symbol('k', real=True) eq1 = f(x).diff(x, 2) + 2*f(x).diff(x) eq2 = f(x).diff(x, 2) - 3*f(x).diff(x) + 2*f(x) eq3 = f(x).diff(x, 2) - f(x) eq4 = f(x).diff(x, 3) + f(x).diff(x, 2) - 6*f(x).diff(x) eq5 = 6*f(x).diff(x, 2) - 11*f(x).diff(x) + 4*f(x) eq6 = Eq(f(x).diff(x, 2) + 2*f(x).diff(x) - f(x), 0) eq7 = diff(f(x), x, 3) + diff(f(x), x, 2) - 10*diff(f(x), x) - 6*f(x) eq8 = f(x).diff(x, 4) - f(x).diff(x, 3) - 4*f(x).diff(x, 2) + \ 4*f(x).diff(x) eq9 = f(x).diff(x, 4) + 4*f(x).diff(x, 3) + f(x).diff(x, 2) - \ 4*f(x).diff(x) - 2*f(x) eq10 = f(x).diff(x, 4) - a**2*f(x) eq11 = f(x).diff(x, 2) - 2*k*f(x).diff(x) - 2*f(x) eq12 = f(x).diff(x, 2) + 4*k*f(x).diff(x) - 12*k**2*f(x) eq13 = f(x).diff(x, 4) eq14 = f(x).diff(x, 2) + 4*f(x).diff(x) + 4*f(x) eq15 = 3*f(x).diff(x, 3) + 5*f(x).diff(x, 2) + f(x).diff(x) - f(x) eq16 = f(x).diff(x, 3) - 6*f(x).diff(x, 2) + 12*f(x).diff(x) - 8*f(x) eq17 = f(x).diff(x, 2) - 2*a*f(x).diff(x) + a**2*f(x) eq18 = f(x).diff(x, 4) + 3*f(x).diff(x, 3) eq19 = f(x).diff(x, 4) - 2*f(x).diff(x, 2) eq20 = f(x).diff(x, 4) + 2*f(x).diff(x, 3) - 11*f(x).diff(x, 2) - \ 12*f(x).diff(x) + 36*f(x) eq21 = 36*f(x).diff(x, 4) - 37*f(x).diff(x, 2) + 4*f(x).diff(x) + 5*f(x) eq22 = f(x).diff(x, 4) - 8*f(x).diff(x, 2) + 16*f(x) eq23 = f(x).diff(x, 2) - 2*f(x).diff(x) + 5*f(x) eq24 = f(x).diff(x, 2) - f(x).diff(x) + f(x) eq25 = f(x).diff(x, 4) + 5*f(x).diff(x, 2) + 6*f(x) eq26 = f(x).diff(x, 2) - 4*f(x).diff(x) + 20*f(x) eq27 = f(x).diff(x, 4) + 4*f(x).diff(x, 2) + 4*f(x) eq28 = f(x).diff(x, 3) + 8*f(x) eq29 = f(x).diff(x, 4) + 4*f(x).diff(x, 2) eq30 = f(x).diff(x, 5) + 2*f(x).diff(x, 3) + f(x).diff(x) eq31 = f(x).diff(x, 4) + f(x).diff(x, 2) + f(x) eq32 = f(x).diff(x, 4) + 4*f(x).diff(x, 2) + f(x) sol1 = Eq(f(x), C1 + C2*exp(-2*x)) sol2 = Eq(f(x), (C1 + C2*exp(x))*exp(x)) sol3 = Eq(f(x), C1*exp(x) + C2*exp(-x)) sol4 = Eq(f(x), C1 + C2*exp(-3*x) + C3*exp(2*x)) sol5 = Eq(f(x), C1*exp(x/2) + C2*exp(4*x/3)) sol6 = Eq(f(x), C1*exp(x*(-1 + sqrt(2))) + C2*exp(x*(-sqrt(2) - 1))) sol7 = Eq(f(x), C1*exp(3*x) + C2*exp(x*(-2 - sqrt(2))) + C3*exp(x*(-2 + sqrt(2)))) sol8 = Eq(f(x), C1 + C2*exp(x) + C3*exp(-2*x) + C4*exp(2*x)) sol9 = Eq(f(x), C1*exp(x) + C2*exp(-x) + C3*exp(x*(-2 + sqrt(2))) + C4*exp(x*(-2 - sqrt(2)))) sol10 = Eq(f(x), C1*sin(x*sqrt(a)) + C2*cos(x*sqrt(a)) + C3*exp(x*sqrt(a)) + C4*exp(-x*sqrt(a))) sol11 = Eq(f(x), C1*exp(x*(k - sqrt(k**2 + 2))) + C2*exp(x*(k + sqrt(k**2 + 2)))) sol12 = Eq(f(x), C1*exp(-6*k*x) + C2*exp(2*k*x)) sol13 = Eq(f(x), C1 + C2*x + C3*x**2 + C4*x**3) sol14 = Eq(f(x), (C1 + C2*x)*exp(-2*x)) sol15 = Eq(f(x), (C1 + C2*x)*exp(-x) + C3*exp(x/3)) sol16 = Eq(f(x), (C1 + C2*x + C3*x**2)*exp(2*x)) sol17 = Eq(f(x), (C1 + C2*x)*exp(a*x)) sol18 = Eq(f(x), C1 + C2*x + C3*x**2 + C4*exp(-3*x)) sol19 = Eq(f(x), C1 + C2*x + C3*exp(x*sqrt(2)) + C4*exp(-x*sqrt(2))) sol20 = Eq(f(x), (C1 + C2*x)*exp(-3*x) + (C3 + C4*x)*exp(2*x)) sol21 = Eq(f(x), C1*exp(x/2) + C2*exp(-x) + C3*exp(-x/3) + C4*exp(5*x/6)) sol22 = Eq(f(x), (C1 + C2*x)*exp(-2*x) + (C3 + C4*x)*exp(2*x)) sol23 = Eq(f(x), (C1*sin(2*x) + C2*cos(2*x))*exp(x)) sol24 = Eq(f(x), (C1*sin(x*sqrt(3)/2) + C2*cos(x*sqrt(3)/2))*exp(x/2)) sol25 = Eq(f(x), C1*cos(x*sqrt(3)) + C2*sin(x*sqrt(3)) + C3*sin(x*sqrt(2)) + C4*cos(x*sqrt(2))) sol26 = Eq(f(x), (C1*sin(4*x) + C2*cos(4*x))*exp(2*x)) sol27 = Eq(f(x), (C1 + C2*x)*sin(x*sqrt(2)) + (C3 + C4*x)*cos(x*sqrt(2))) sol28 = Eq(f(x), (C1*sin(x*sqrt(3)) + C2*cos(x*sqrt(3)))*exp(x) + C3*exp(-2*x)) sol29 = Eq(f(x), C1 + C2*sin(2*x) + C3*cos(2*x) + C4*x) sol30 = Eq(f(x), C1 + (C2 + C3*x)*sin(x) + (C4 + C5*x)*cos(x)) sol31 = Eq(f(x), (C1*sin(sqrt(3)*x/2) + C2*cos(sqrt(3)*x/2))/sqrt(exp(x)) + (C3*sin(sqrt(3)*x/2) + C4*cos(sqrt(3)*x/2))*sqrt(exp(x))) sol32 = Eq(f(x), C1*sin(x*sqrt(-sqrt(3) + 2)) + C2*sin(x*sqrt(sqrt(3) + 2)) + C3*cos(x*sqrt(-sqrt(3) + 2)) + C4*cos(x*sqrt(sqrt(3) + 2))) sol1s = constant_renumber(sol1) sol2s = constant_renumber(sol2) sol3s = constant_renumber(sol3) sol4s = constant_renumber(sol4) sol5s = constant_renumber(sol5) sol6s = constant_renumber(sol6) sol7s = constant_renumber(sol7) sol8s = constant_renumber(sol8) sol9s = constant_renumber(sol9) sol10s = constant_renumber(sol10) sol11s = constant_renumber(sol11) sol12s = constant_renumber(sol12) sol13s = constant_renumber(sol13) sol14s = constant_renumber(sol14) sol15s = constant_renumber(sol15) sol16s = constant_renumber(sol16) sol17s = constant_renumber(sol17) sol18s = constant_renumber(sol18) sol19s = constant_renumber(sol19) sol20s = constant_renumber(sol20) sol21s = constant_renumber(sol21) sol22s = constant_renumber(sol22) sol23s = constant_renumber(sol23) sol24s = constant_renumber(sol24) sol25s = constant_renumber(sol25) sol26s = constant_renumber(sol26) sol27s = constant_renumber(sol27) sol28s = constant_renumber(sol28) sol29s = constant_renumber(sol29) sol30s = constant_renumber(sol30) assert dsolve(eq1) in (sol1, sol1s) assert dsolve(eq2) in (sol2, sol2s) assert dsolve(eq3) in (sol3, sol3s) assert dsolve(eq4) in (sol4, sol4s) assert dsolve(eq5) in (sol5, sol5s) assert dsolve(eq6) in (sol6, sol6s) assert dsolve(eq7) in (sol7, sol7s) assert dsolve(eq8) in (sol8, sol8s) assert dsolve(eq9) in (sol9, sol9s) assert dsolve(eq10) in (sol10, sol10s) assert dsolve(eq11) in (sol11, sol11s) assert dsolve(eq12) in (sol12, sol12s) assert dsolve(eq13) in (sol13, sol13s) assert dsolve(eq14) in (sol14, sol14s) assert dsolve(eq15) in (sol15, sol15s) assert dsolve(eq16) in (sol16, sol16s) assert dsolve(eq17) in (sol17, sol17s) assert dsolve(eq18) in (sol18, sol18s) assert dsolve(eq19) in (sol19, sol19s) assert dsolve(eq20) in (sol20, sol20s) assert dsolve(eq21) in (sol21, sol21s) assert dsolve(eq22) in (sol22, sol22s) assert dsolve(eq23) in (sol23, sol23s) assert dsolve(eq24) in (sol24, sol24s) assert dsolve(eq25) in (sol25, sol25s) assert dsolve(eq26) in (sol26, sol26s) assert dsolve(eq27) in (sol27, sol27s) assert dsolve(eq28) in (sol28, sol28s) assert dsolve(eq29) in (sol29, sol29s) assert dsolve(eq30) in (sol30, sol30s) assert dsolve(eq31) in (sol31,) assert dsolve(eq32) in (sol32,) assert checkodesol(eq1, sol1, order=2, solve_for_func=False)[0] assert checkodesol(eq2, sol2, order=2, solve_for_func=False)[0] assert checkodesol(eq3, sol3, order=2, solve_for_func=False)[0] assert checkodesol(eq4, sol4, order=3, solve_for_func=False)[0] assert checkodesol(eq5, sol5, order=2, solve_for_func=False)[0] assert checkodesol(eq6, sol6, order=2, solve_for_func=False)[0] assert checkodesol(eq7, sol7, order=3, solve_for_func=False)[0] assert checkodesol(eq8, sol8, order=4, solve_for_func=False)[0] assert checkodesol(eq9, sol9, order=4, solve_for_func=False)[0] assert checkodesol(eq10, sol10, order=4, solve_for_func=False)[0] assert checkodesol(eq11, sol11, order=2, solve_for_func=False)[0] assert checkodesol(eq12, sol12, order=2, solve_for_func=False)[0] assert checkodesol(eq13, sol13, order=4, solve_for_func=False)[0] assert checkodesol(eq14, sol14, order=2, solve_for_func=False)[0] assert checkodesol(eq15, sol15, order=3, solve_for_func=False)[0] assert checkodesol(eq16, sol16, order=3, solve_for_func=False)[0] assert checkodesol(eq17, sol17, order=2, solve_for_func=False)[0] assert checkodesol(eq18, sol18, order=4, solve_for_func=False)[0] assert checkodesol(eq19, sol19, order=4, solve_for_func=False)[0] assert checkodesol(eq20, sol20, order=4, solve_for_func=False)[0] assert checkodesol(eq21, sol21, order=4, solve_for_func=False)[0] assert checkodesol(eq22, sol22, order=4, solve_for_func=False)[0] assert checkodesol(eq23, sol23, order=2, solve_for_func=False)[0] assert checkodesol(eq24, sol24, order=2, solve_for_func=False)[0] assert checkodesol(eq25, sol25, order=4, solve_for_func=False)[0] assert checkodesol(eq26, sol26, order=2, solve_for_func=False)[0] assert checkodesol(eq27, sol27, order=4, solve_for_func=False)[0] assert checkodesol(eq28, sol28, order=3, solve_for_func=False)[0] assert checkodesol(eq29, sol29, order=4, solve_for_func=False)[0] assert checkodesol(eq30, sol30, order=5, solve_for_func=False)[0] assert checkodesol(eq31, sol31, order=4, solve_for_func=False)[0] assert checkodesol(eq32, sol32, order=4, solve_for_func=False)[0] # Issue #15237 eqn = Derivative(x*f(x), x, x, x) hint = 'nth_linear_constant_coeff_homogeneous' raises(ValueError, lambda: dsolve(eqn, f(x), hint, prep=True)) raises(ValueError, lambda: dsolve(eqn, f(x), hint, prep=False)) def test_nth_linear_constant_coeff_homogeneous_rootof(): # One real root, two complex conjugate pairs eq = f(x).diff(x, 5) + 11*f(x).diff(x) - 2*f(x) r1, r2, r3, r4, r5 = [rootof(x**5 + 11*x - 2, n) for n in range(5)] sol = Eq(f(x), C5*exp(r1*x) + exp(re(r2)*x) * (C1*sin(im(r2)*x) + C2*cos(im(r2)*x)) + exp(re(r4)*x) * (C3*sin(im(r4)*x) + C4*cos(im(r4)*x)) ) assert dsolve(eq) == sol # FIXME: assert checkodesol(eq, sol) == (True, [0]) # Hangs... # Three real roots, one complex conjugate pair eq = f(x).diff(x,5) - 3*f(x).diff(x) + f(x) r1, r2, r3, r4, r5 = [rootof(x**5 - 3*x + 1, n) for n in range(5)] sol = Eq(f(x), C3*exp(r1*x) + C4*exp(r2*x) + C5*exp(r3*x) + exp(re(r4)*x) * (C1*sin(im(r4)*x) + C2*cos(im(r4)*x)) ) assert dsolve(eq) == sol # FIXME: assert checkodesol(eq, sol) == (True, [0]) # Hangs... # Five distinct real roots eq = f(x).diff(x,5) - 100*f(x).diff(x,3) + 1000*f(x).diff(x) + f(x) r1, r2, r3, r4, r5 = [rootof(x**5 - 100*x**3 + 1000*x + 1, n) for n in range(5)] sol = Eq(f(x), C1*exp(r1*x) + C2*exp(r2*x) + C3*exp(r3*x) + C4*exp(r4*x) + C5*exp(r5*x)) assert dsolve(eq) == sol # FIXME: assert checkodesol(eq, sol) == (True, [0]) # Hangs... # Rational root and unsolvable quintic eq = f(x).diff(x, 6) - 6*f(x).diff(x, 5) + 5*f(x).diff(x, 4) + 10*f(x).diff(x) - 50 * f(x) r2, r3, r4, r5, r6 = [rootof(x**5 - x**4 + 10, n) for n in range(5)] sol = Eq(f(x), C5*exp(5*x) + C6*exp(x*r2) + exp(re(r3)*x) * (C1*sin(im(r3)*x) + C2*cos(im(r3)*x)) + exp(re(r5)*x) * (C3*sin(im(r5)*x) + C4*cos(im(r5)*x)) ) assert dsolve(eq) == sol # FIXME: assert checkodesol(eq, sol) == (True, [0]) # Hangs... # Five double roots (this is (x**5 - x + 1)**2) eq = f(x).diff(x, 10) - 2*f(x).diff(x, 6) + 2*f(x).diff(x, 5) + f(x).diff(x, 2) - 2*f(x).diff(x, 1) + f(x) r1, r2, r3, r4, r5 = [rootof(x**5 - x + 1, n) for n in range(5)] sol = Eq(f(x), (C1 + C2 *x)*exp(r1*x) + exp(re(r2)*x) * ((C3 + C4*x)*sin(im(r2)*x) + (C5 + C6 *x)*cos(im(r2)*x)) + exp(re(r4)*x) * ((C7 + C8*x)*sin(im(r4)*x) + (C9 + C10*x)*cos(im(r4)*x)) ) assert dsolve(eq) == sol # FIXME: assert checkodesol(eq, sol) == (True, [0]) # Hangs... def test_nth_linear_constant_coeff_homogeneous_irrational(): our_hint='nth_linear_constant_coeff_homogeneous' eq = Eq(sqrt(2) * f(x).diff(x,x,x) + f(x).diff(x), 0) sol = Eq(f(x), C1 + C2*sin(2**(S(3)/4)*x/2) + C3*cos(2**(S(3)/4)*x/2)) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint) == sol assert dsolve(eq, f(x)) == sol assert checkodesol(eq, sol, order=3, solve_for_func=False)[0] E = exp(1) eq = Eq(E * f(x).diff(x,x,x) + f(x).diff(x), 0) sol = Eq(f(x), C1 + C2*sin(x/sqrt(E)) + C3*cos(x/sqrt(E))) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint) == sol assert dsolve(eq, f(x)) == sol assert checkodesol(eq, sol, order=3, solve_for_func=False)[0] eq = Eq(pi * f(x).diff(x,x,x) + f(x).diff(x), 0) sol = Eq(f(x), C1 + C2*sin(x/sqrt(pi)) + C3*cos(x/sqrt(pi))) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint) == sol assert dsolve(eq, f(x)) == sol assert checkodesol(eq, sol, order=3, solve_for_func=False)[0] eq = Eq(I * f(x).diff(x,x,x) + f(x).diff(x), 0) sol = Eq(f(x), C1 + C2*exp(-sqrt(I)*x) + C3*exp(sqrt(I)*x)) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint) == sol assert dsolve(eq, f(x)) == sol assert checkodesol(eq, sol, order=3, solve_for_func=False)[0] @XFAIL @slow def test_nth_linear_constant_coeff_homogeneous_rootof_sol(): if ON_TRAVIS: skip("Too slow for travis.") eq = f(x).diff(x, 5) + 11*f(x).diff(x) - 2*f(x) sol = Eq(f(x), C1*exp(x*rootof(x**5 + 11*x - 2, 0)) + C2*exp(x*rootof(x**5 + 11*x - 2, 1)) + C3*exp(x*rootof(x**5 + 11*x - 2, 2)) + C4*exp(x*rootof(x**5 + 11*x - 2, 3)) + C5*exp(x*rootof(x**5 + 11*x - 2, 4))) assert checkodesol(eq, sol, order=5, solve_for_func=False)[0] @XFAIL def test_noncircularized_real_imaginary_parts(): # If this passes, lines numbered 3878-3882 (at the time of this commit) # of sympy/solvers/ode.py for nth_linear_constant_coeff_homogeneous # should be removed. y = sqrt(1+x) i, r = im(y), re(y) assert not (i.has(atan2) and r.has(atan2)) @XFAIL def test_collect_respecting_exponentials(): # If this test passes, lines 1306-1311 (at the time of this commit) # of sympy/solvers/ode.py should be removed. sol = 1 + exp(x/2) assert sol == collect( sol, exp(x/3)) def test_undetermined_coefficients_match(): assert _undetermined_coefficients_match(g(x), x) == {'test': False} assert _undetermined_coefficients_match(sin(2*x + sqrt(5)), x) == \ {'test': True, 'trialset': set([cos(2*x + sqrt(5)), sin(2*x + sqrt(5))])} assert _undetermined_coefficients_match(sin(x)*cos(x), x) == \ {'test': False} s = set([cos(x), x*cos(x), x**2*cos(x), x**2*sin(x), x*sin(x), sin(x)]) assert _undetermined_coefficients_match(sin(x)*(x**2 + x + 1), x) == \ {'test': True, 'trialset': s} assert _undetermined_coefficients_match( sin(x)*x**2 + sin(x)*x + sin(x), x) == {'test': True, 'trialset': s} assert _undetermined_coefficients_match( exp(2*x)*sin(x)*(x**2 + x + 1), x ) == { 'test': True, 'trialset': set([exp(2*x)*sin(x), x**2*exp(2*x)*sin(x), cos(x)*exp(2*x), x**2*cos(x)*exp(2*x), x*cos(x)*exp(2*x), x*exp(2*x)*sin(x)])} assert _undetermined_coefficients_match(1/sin(x), x) == {'test': False} assert _undetermined_coefficients_match(log(x), x) == {'test': False} assert _undetermined_coefficients_match(2**(x)*(x**2 + x + 1), x) == \ {'test': True, 'trialset': set([2**x, x*2**x, x**2*2**x])} assert _undetermined_coefficients_match(x**y, x) == {'test': False} assert _undetermined_coefficients_match(exp(x)*exp(2*x + 1), x) == \ {'test': True, 'trialset': set([exp(1 + 3*x)])} assert _undetermined_coefficients_match(sin(x)*(x**2 + x + 1), x) == \ {'test': True, 'trialset': set([x*cos(x), x*sin(x), x**2*cos(x), x**2*sin(x), cos(x), sin(x)])} assert _undetermined_coefficients_match(sin(x)*(x + sin(x)), x) == \ {'test': False} assert _undetermined_coefficients_match(sin(x)*(x + sin(2*x)), x) == \ {'test': False} assert _undetermined_coefficients_match(sin(x)*tan(x), x) == \ {'test': False} assert _undetermined_coefficients_match( x**2*sin(x)*exp(x) + x*sin(x) + x, x ) == { 'test': True, 'trialset': set([x**2*cos(x)*exp(x), x, cos(x), S(1), exp(x)*sin(x), sin(x), x*exp(x)*sin(x), x*cos(x), x*cos(x)*exp(x), x*sin(x), cos(x)*exp(x), x**2*exp(x)*sin(x)])} assert _undetermined_coefficients_match(4*x*sin(x - 2), x) == { 'trialset': set([x*cos(x - 2), x*sin(x - 2), cos(x - 2), sin(x - 2)]), 'test': True, } assert _undetermined_coefficients_match(2**x*x, x) == \ {'test': True, 'trialset': set([2**x, x*2**x])} assert _undetermined_coefficients_match(2**x*exp(2*x), x) == \ {'test': True, 'trialset': set([2**x*exp(2*x)])} assert _undetermined_coefficients_match(exp(-x)/x, x) == \ {'test': False} # Below are from Ordinary Differential Equations, # Tenenbaum and Pollard, pg. 231 assert _undetermined_coefficients_match(S(4), x) == \ {'test': True, 'trialset': set([S(1)])} assert _undetermined_coefficients_match(12*exp(x), x) == \ {'test': True, 'trialset': set([exp(x)])} assert _undetermined_coefficients_match(exp(I*x), x) == \ {'test': True, 'trialset': set([exp(I*x)])} assert _undetermined_coefficients_match(sin(x), x) == \ {'test': True, 'trialset': set([cos(x), sin(x)])} assert _undetermined_coefficients_match(cos(x), x) == \ {'test': True, 'trialset': set([cos(x), sin(x)])} assert _undetermined_coefficients_match(8 + 6*exp(x) + 2*sin(x), x) == \ {'test': True, 'trialset': set([S(1), cos(x), sin(x), exp(x)])} assert _undetermined_coefficients_match(x**2, x) == \ {'test': True, 'trialset': set([S(1), x, x**2])} assert _undetermined_coefficients_match(9*x*exp(x) + exp(-x), x) == \ {'test': True, 'trialset': set([x*exp(x), exp(x), exp(-x)])} assert _undetermined_coefficients_match(2*exp(2*x)*sin(x), x) == \ {'test': True, 'trialset': set([exp(2*x)*sin(x), cos(x)*exp(2*x)])} assert _undetermined_coefficients_match(x - sin(x), x) == \ {'test': True, 'trialset': set([S(1), x, cos(x), sin(x)])} assert _undetermined_coefficients_match(x**2 + 2*x, x) == \ {'test': True, 'trialset': set([S(1), x, x**2])} assert _undetermined_coefficients_match(4*x*sin(x), x) == \ {'test': True, 'trialset': set([x*cos(x), x*sin(x), cos(x), sin(x)])} assert _undetermined_coefficients_match(x*sin(2*x), x) == \ {'test': True, 'trialset': set([x*cos(2*x), x*sin(2*x), cos(2*x), sin(2*x)])} assert _undetermined_coefficients_match(x**2*exp(-x), x) == \ {'test': True, 'trialset': set([x*exp(-x), x**2*exp(-x), exp(-x)])} assert _undetermined_coefficients_match(2*exp(-x) - x**2*exp(-x), x) == \ {'test': True, 'trialset': set([x*exp(-x), x**2*exp(-x), exp(-x)])} assert _undetermined_coefficients_match(exp(-2*x) + x**2, x) == \ {'test': True, 'trialset': set([S(1), x, x**2, exp(-2*x)])} assert _undetermined_coefficients_match(x*exp(-x), x) == \ {'test': True, 'trialset': set([x*exp(-x), exp(-x)])} assert _undetermined_coefficients_match(x + exp(2*x), x) == \ {'test': True, 'trialset': set([S(1), x, exp(2*x)])} assert _undetermined_coefficients_match(sin(x) + exp(-x), x) == \ {'test': True, 'trialset': set([cos(x), sin(x), exp(-x)])} assert _undetermined_coefficients_match(exp(x), x) == \ {'test': True, 'trialset': set([exp(x)])} # converted from sin(x)**2 assert _undetermined_coefficients_match(S(1)/2 - cos(2*x)/2, x) == \ {'test': True, 'trialset': set([S(1), cos(2*x), sin(2*x)])} # converted from exp(2*x)*sin(x)**2 assert _undetermined_coefficients_match( exp(2*x)*(S(1)/2 + cos(2*x)/2), x ) == { 'test': True, 'trialset': set([exp(2*x)*sin(2*x), cos(2*x)*exp(2*x), exp(2*x)])} assert _undetermined_coefficients_match(2*x + sin(x) + cos(x), x) == \ {'test': True, 'trialset': set([S(1), x, cos(x), sin(x)])} # converted from sin(2*x)*sin(x) assert _undetermined_coefficients_match(cos(x)/2 - cos(3*x)/2, x) == \ {'test': True, 'trialset': set([cos(x), cos(3*x), sin(x), sin(3*x)])} assert _undetermined_coefficients_match(cos(x**2), x) == {'test': False} assert _undetermined_coefficients_match(2**(x**2), x) == {'test': False} @slow def test_nth_linear_constant_coeff_undetermined_coefficients(): hint = 'nth_linear_constant_coeff_undetermined_coefficients' g = exp(-x) f2 = f(x).diff(x, 2) c = 3*f(x).diff(x, 3) + 5*f2 + f(x).diff(x) - f(x) - x eq1 = c - x*g eq2 = c - g # 3-27 below are from Ordinary Differential Equations, # Tenenbaum and Pollard, pg. 231 eq3 = f2 + 3*f(x).diff(x) + 2*f(x) - 4 eq4 = f2 + 3*f(x).diff(x) + 2*f(x) - 12*exp(x) eq5 = f2 + 3*f(x).diff(x) + 2*f(x) - exp(I*x) eq6 = f2 + 3*f(x).diff(x) + 2*f(x) - sin(x) eq7 = f2 + 3*f(x).diff(x) + 2*f(x) - cos(x) eq8 = f2 + 3*f(x).diff(x) + 2*f(x) - (8 + 6*exp(x) + 2*sin(x)) eq9 = f2 + f(x).diff(x) + f(x) - x**2 eq10 = f2 - 2*f(x).diff(x) - 8*f(x) - 9*x*exp(x) - 10*exp(-x) eq11 = f2 - 3*f(x).diff(x) - 2*exp(2*x)*sin(x) eq12 = f(x).diff(x, 4) - 2*f2 + f(x) - x + sin(x) eq13 = f2 + f(x).diff(x) - x**2 - 2*x eq14 = f2 + f(x).diff(x) - x - sin(2*x) eq15 = f2 + f(x) - 4*x*sin(x) eq16 = f2 + 4*f(x) - x*sin(2*x) eq17 = f2 + 2*f(x).diff(x) + f(x) - x**2*exp(-x) eq18 = f(x).diff(x, 3) + 3*f2 + 3*f(x).diff(x) + f(x) - 2*exp(-x) + \ x**2*exp(-x) eq19 = f2 + 3*f(x).diff(x) + 2*f(x) - exp(-2*x) - x**2 eq20 = f2 - 3*f(x).diff(x) + 2*f(x) - x*exp(-x) eq21 = f2 + f(x).diff(x) - 6*f(x) - x - exp(2*x) eq22 = f2 + f(x) - sin(x) - exp(-x) eq23 = f(x).diff(x, 3) - 3*f2 + 3*f(x).diff(x) - f(x) - exp(x) # sin(x)**2 eq24 = f2 + f(x) - S(1)/2 - cos(2*x)/2 # exp(2*x)*sin(x)**2 eq25 = f(x).diff(x, 3) - f(x).diff(x) - exp(2*x)*(S(1)/2 - cos(2*x)/2) eq26 = (f(x).diff(x, 5) + 2*f(x).diff(x, 3) + f(x).diff(x) - 2*x - sin(x) - cos(x)) # sin(2*x)*sin(x), skip 3127 for now, match bug eq27 = f2 + f(x) - cos(x)/2 + cos(3*x)/2 eq28 = f(x).diff(x) - 1 sol1 = Eq(f(x), -1 - x + (C1 + C2*x - 3*x**2/32 - x**3/24)*exp(-x) + C3*exp(x/3)) sol2 = Eq(f(x), -1 - x + (C1 + C2*x - x**2/8)*exp(-x) + C3*exp(x/3)) sol3 = Eq(f(x), 2 + C1*exp(-x) + C2*exp(-2*x)) sol4 = Eq(f(x), 2*exp(x) + C1*exp(-x) + C2*exp(-2*x)) sol5 = Eq(f(x), C1*exp(-2*x) + C2*exp(-x) + exp(I*x)/10 - 3*I*exp(I*x)/10) sol6 = Eq(f(x), -3*cos(x)/10 + sin(x)/10 + C1*exp(-x) + C2*exp(-2*x)) sol7 = Eq(f(x), cos(x)/10 + 3*sin(x)/10 + C1*exp(-x) + C2*exp(-2*x)) sol8 = Eq(f(x), 4 - 3*cos(x)/5 + sin(x)/5 + exp(x) + C1*exp(-x) + C2*exp(-2*x)) sol9 = Eq(f(x), -2*x + x**2 + (C1*sin(x*sqrt(3)/2) + C2*cos(x*sqrt(3)/2))*exp(-x/2)) sol10 = Eq(f(x), -x*exp(x) - 2*exp(-x) + C1*exp(-2*x) + C2*exp(4*x)) sol11 = Eq(f(x), C1 + C2*exp(3*x) + (-3*sin(x) - cos(x))*exp(2*x)/5) sol12 = Eq(f(x), x - sin(x)/4 + (C1 + C2*x)*exp(-x) + (C3 + C4*x)*exp(x)) sol13 = Eq(f(x), C1 + x**3/3 + C2*exp(-x)) sol14 = Eq(f(x), C1 - x - sin(2*x)/5 - cos(2*x)/10 + x**2/2 + C2*exp(-x)) sol15 = Eq(f(x), (C1 + x)*sin(x) + (C2 - x**2)*cos(x)) sol16 = Eq(f(x), (C1 + x/16)*sin(2*x) + (C2 - x**2/8)*cos(2*x)) sol17 = Eq(f(x), (C1 + C2*x + x**4/12)*exp(-x)) sol18 = Eq(f(x), (C1 + C2*x + C3*x**2 - x**5/60 + x**3/3)*exp(-x)) sol19 = Eq(f(x), S(7)/4 - 3*x/2 + x**2/2 + C1*exp(-x) + (C2 - x)*exp(-2*x)) sol20 = Eq(f(x), C1*exp(x) + C2*exp(2*x) + (6*x + 5)*exp(-x)/36) sol21 = Eq(f(x), -S(1)/36 - x/6 + C1*exp(-3*x) + (C2 + x/5)*exp(2*x)) sol22 = Eq(f(x), C1*sin(x) + (C2 - x/2)*cos(x) + exp(-x)/2) sol23 = Eq(f(x), (C1 + C2*x + C3*x**2 + x**3/6)*exp(x)) sol24 = Eq(f(x), S(1)/2 - cos(2*x)/6 + C1*sin(x) + C2*cos(x)) sol25 = Eq(f(x), C1 + C2*exp(-x) + C3*exp(x) + (-21*sin(2*x) + 27*cos(2*x) + 130)*exp(2*x)/1560) sol26 = Eq(f(x), C1 + (C2 + C3*x - x**2/8)*sin(x) + (C4 + C5*x + x**2/8)*cos(x) + x**2) sol27 = Eq(f(x), cos(3*x)/16 + C1*cos(x) + (C2 + x/4)*sin(x)) sol28 = Eq(f(x), C1 + x) sol1s = constant_renumber(sol1) sol2s = constant_renumber(sol2) sol3s = constant_renumber(sol3) sol4s = constant_renumber(sol4) sol5s = constant_renumber(sol5) sol6s = constant_renumber(sol6) sol7s = constant_renumber(sol7) sol8s = constant_renumber(sol8) sol9s = constant_renumber(sol9) sol10s = constant_renumber(sol10) sol11s = constant_renumber(sol11) sol12s = constant_renumber(sol12) sol13s = constant_renumber(sol13) sol14s = constant_renumber(sol14) sol15s = constant_renumber(sol15) sol16s = constant_renumber(sol16) sol17s = constant_renumber(sol17) sol18s = constant_renumber(sol18) sol19s = constant_renumber(sol19) sol20s = constant_renumber(sol20) sol21s = constant_renumber(sol21) sol22s = constant_renumber(sol22) sol23s = constant_renumber(sol23) sol24s = constant_renumber(sol24) sol25s = constant_renumber(sol25) sol26s = constant_renumber(sol26) sol27s = constant_renumber(sol27) assert dsolve(eq1, hint=hint) in (sol1, sol1s) assert dsolve(eq2, hint=hint) in (sol2, sol2s) assert dsolve(eq3, hint=hint) in (sol3, sol3s) assert dsolve(eq4, hint=hint) in (sol4, sol4s) assert dsolve(eq5, hint=hint) in (sol5, sol5s) assert dsolve(eq6, hint=hint) in (sol6, sol6s) assert dsolve(eq7, hint=hint) in (sol7, sol7s) assert dsolve(eq8, hint=hint) in (sol8, sol8s) assert dsolve(eq9, hint=hint) in (sol9, sol9s) assert dsolve(eq10, hint=hint) in (sol10, sol10s) assert dsolve(eq11, hint=hint) in (sol11, sol11s) assert dsolve(eq12, hint=hint) in (sol12, sol12s) assert dsolve(eq13, hint=hint) in (sol13, sol13s) assert dsolve(eq14, hint=hint) in (sol14, sol14s) assert dsolve(eq15, hint=hint) in (sol15, sol15s) assert dsolve(eq16, hint=hint) in (sol16, sol16s) assert dsolve(eq17, hint=hint) in (sol17, sol17s) assert dsolve(eq18, hint=hint) in (sol18, sol18s) assert dsolve(eq19, hint=hint) in (sol19, sol19s) assert dsolve(eq20, hint=hint) in (sol20, sol20s) assert dsolve(eq21, hint=hint) in (sol21, sol21s) assert dsolve(eq22, hint=hint) in (sol22, sol22s) assert dsolve(eq23, hint=hint) in (sol23, sol23s) assert dsolve(eq24, hint=hint) in (sol24, sol24s) assert dsolve(eq25, hint=hint) in (sol25, sol25s) assert dsolve(eq26, hint=hint) in (sol26, sol26s) assert dsolve(eq27, hint=hint) in (sol27, sol27s) assert dsolve(eq28, hint=hint) == sol28 assert checkodesol(eq1, sol1, order=3, solve_for_func=False)[0] assert checkodesol(eq2, sol2, order=3, solve_for_func=False)[0] assert checkodesol(eq3, sol3, order=2, solve_for_func=False)[0] assert checkodesol(eq4, sol4, order=2, solve_for_func=False)[0] assert checkodesol(eq5, sol5, order=2, solve_for_func=False)[0] assert checkodesol(eq6, sol6, order=2, solve_for_func=False)[0] assert checkodesol(eq7, sol7, order=2, solve_for_func=False)[0] assert checkodesol(eq8, sol8, order=2, solve_for_func=False)[0] assert checkodesol(eq9, sol9, order=2, solve_for_func=False)[0] assert checkodesol(eq10, sol10, order=2, solve_for_func=False)[0] assert checkodesol(eq11, sol11, order=2, solve_for_func=False)[0] assert checkodesol(eq12, sol12, order=4, solve_for_func=False)[0] assert checkodesol(eq13, sol13, order=2, solve_for_func=False)[0] assert checkodesol(eq14, sol14, order=2, solve_for_func=False)[0] assert checkodesol(eq15, sol15, order=2, solve_for_func=False)[0] assert checkodesol(eq16, sol16, order=2, solve_for_func=False)[0] assert checkodesol(eq17, sol17, order=2, solve_for_func=False)[0] assert checkodesol(eq18, sol18, order=3, solve_for_func=False)[0] assert checkodesol(eq19, sol19, order=2, solve_for_func=False)[0] assert checkodesol(eq20, sol20, order=2, solve_for_func=False)[0] assert checkodesol(eq21, sol21, order=2, solve_for_func=False)[0] assert checkodesol(eq22, sol22, order=2, solve_for_func=False)[0] assert checkodesol(eq23, sol23, order=3, solve_for_func=False)[0] assert checkodesol(eq24, sol24, order=2, solve_for_func=False)[0] assert checkodesol(eq25, sol25, order=3, solve_for_func=False)[0] assert checkodesol(eq26, sol26, order=5, solve_for_func=False)[0] assert checkodesol(eq27, sol27, order=2, solve_for_func=False)[0] assert checkodesol(eq28, sol28, order=1, solve_for_func=False)[0] def test_issue_5787(): # This test case is to show the classification of imaginary constants under # nth_linear_constant_coeff_undetermined_coefficients eq = Eq(diff(f(x), x), I*f(x) + S(1)/2 - I) our_hint = 'nth_linear_constant_coeff_undetermined_coefficients' assert our_hint in classify_ode(eq) @XFAIL def test_nth_linear_constant_coeff_undetermined_coefficients_imaginary_exp(): # Equivalent to eq26 in # test_nth_linear_constant_coeff_undetermined_coefficients above. # This fails because the algorithm for undetermined coefficients # doesn't know to multiply exp(I*x) by sufficient x because it is linearly # dependent on sin(x) and cos(x). hint = 'nth_linear_constant_coeff_undetermined_coefficients' eq26a = f(x).diff(x, 5) + 2*f(x).diff(x, 3) + f(x).diff(x) - 2*x - exp(I*x) sol26 = Eq(f(x), C1 + (C2 + C3*x - x**2/8)*sin(x) + (C4 + C5*x + x**2/8)*cos(x) + x**2) assert dsolve(eq26a, hint=hint) == sol26 assert checkodesol(eq26a, sol26, order=5, solve_for_func=False)[0] @slow def test_nth_linear_constant_coeff_variation_of_parameters(): hint = 'nth_linear_constant_coeff_variation_of_parameters' g = exp(-x) f2 = f(x).diff(x, 2) c = 3*f(x).diff(x, 3) + 5*f2 + f(x).diff(x) - f(x) - x eq1 = c - x*g eq2 = c - g eq3 = f(x).diff(x) - 1 eq4 = f2 + 3*f(x).diff(x) + 2*f(x) - 4 eq5 = f2 + 3*f(x).diff(x) + 2*f(x) - 12*exp(x) eq6 = f2 - 2*f(x).diff(x) - 8*f(x) - 9*x*exp(x) - 10*exp(-x) eq7 = f2 + 2*f(x).diff(x) + f(x) - x**2*exp(-x) eq8 = f2 - 3*f(x).diff(x) + 2*f(x) - x*exp(-x) eq9 = f(x).diff(x, 3) - 3*f2 + 3*f(x).diff(x) - f(x) - exp(x) eq10 = f2 + 2*f(x).diff(x) + f(x) - exp(-x)/x eq11 = f2 + f(x) - 1/sin(x)*1/cos(x) eq12 = f(x).diff(x, 4) - 1/x sol1 = Eq(f(x), -1 - x + (C1 + C2*x - 3*x**2/32 - x**3/24)*exp(-x) + C3*exp(x/3)) sol2 = Eq(f(x), -1 - x + (C1 + C2*x - x**2/8)*exp(-x) + C3*exp(x/3)) sol3 = Eq(f(x), C1 + x) sol4 = Eq(f(x), 2 + C1*exp(-x) + C2*exp(-2*x)) sol5 = Eq(f(x), 2*exp(x) + C1*exp(-x) + C2*exp(-2*x)) sol6 = Eq(f(x), -x*exp(x) - 2*exp(-x) + C1*exp(-2*x) + C2*exp(4*x)) sol7 = Eq(f(x), (C1 + C2*x + x**4/12)*exp(-x)) sol8 = Eq(f(x), C1*exp(x) + C2*exp(2*x) + (6*x + 5)*exp(-x)/36) sol9 = Eq(f(x), (C1 + C2*x + C3*x**2 + x**3/6)*exp(x)) sol10 = Eq(f(x), (C1 + x*(C2 + log(x)))*exp(-x)) sol11 = Eq(f(x), cos(x)*(C2 - Integral(1/cos(x), x)) + sin(x)*(C1 + Integral(1/sin(x), x))) sol12 = Eq(f(x), C1 + C2*x + x**3*(C3 + log(x)/6) + C4*x**2) sol1s = constant_renumber(sol1) sol2s = constant_renumber(sol2) sol3s = constant_renumber(sol3) sol4s = constant_renumber(sol4) sol5s = constant_renumber(sol5) sol6s = constant_renumber(sol6) sol7s = constant_renumber(sol7) sol8s = constant_renumber(sol8) sol9s = constant_renumber(sol9) sol10s = constant_renumber(sol10) sol11s = constant_renumber(sol11) sol12s = constant_renumber(sol12) assert dsolve(eq1, hint=hint) in (sol1, sol1s) assert dsolve(eq2, hint=hint) in (sol2, sol2s) assert dsolve(eq3, hint=hint) in (sol3, sol3s) assert dsolve(eq4, hint=hint) in (sol4, sol4s) assert dsolve(eq5, hint=hint) in (sol5, sol5s) assert dsolve(eq6, hint=hint) in (sol6, sol6s) assert dsolve(eq7, hint=hint) in (sol7, sol7s) assert dsolve(eq8, hint=hint) in (sol8, sol8s) assert dsolve(eq9, hint=hint) in (sol9, sol9s) assert dsolve(eq10, hint=hint) in (sol10, sol10s) assert dsolve(eq11, hint=hint + '_Integral') in (sol11, sol11s) assert dsolve(eq12, hint=hint) in (sol12, sol12s) assert checkodesol(eq1, sol1, order=3, solve_for_func=False)[0] assert checkodesol(eq2, sol2, order=3, solve_for_func=False)[0] assert checkodesol(eq3, sol3, order=1, solve_for_func=False)[0] assert checkodesol(eq4, sol4, order=2, solve_for_func=False)[0] assert checkodesol(eq5, sol5, order=2, solve_for_func=False)[0] assert checkodesol(eq6, sol6, order=2, solve_for_func=False)[0] assert checkodesol(eq7, sol7, order=2, solve_for_func=False)[0] assert checkodesol(eq8, sol8, order=2, solve_for_func=False)[0] assert checkodesol(eq9, sol9, order=3, solve_for_func=False)[0] assert checkodesol(eq10, sol10, order=2, solve_for_func=False)[0] assert checkodesol(eq12, sol12, order=4, solve_for_func=False)[0] @slow def test_nth_linear_constant_coeff_variation_of_parameters_simplify_False(): # solve_variation_of_parameters shouldn't attempt to simplify the # Wronskian if simplify=False. If wronskian() ever gets good enough # to simplify the result itself, this test might fail. our_hint = 'nth_linear_constant_coeff_variation_of_parameters_Integral' eq = f(x).diff(x, 5) + 2*f(x).diff(x, 3) + f(x).diff(x) - 2*x - exp(I*x) sol_simp = dsolve(eq, f(x), hint=our_hint, simplify=True) sol_nsimp = dsolve(eq, f(x), hint=our_hint, simplify=False) assert sol_simp != sol_nsimp assert checkodesol(eq, sol_simp, order=5, solve_for_func=False)[0] assert checkodesol(eq, sol_nsimp, order=5, solve_for_func=False)[0] def test_Liouville_ODE(): hint = 'Liouville' # The first part here used to be test_ODE_1() from test_solvers.py eq1 = diff(f(x), x)/x + diff(f(x), x, x)/2 - diff(f(x), x)**2/2 eq1a = diff(x*exp(-f(x)), x, x) # compare to test_unexpanded_Liouville_ODE() below eq2 = (eq1*exp(-f(x))/exp(f(x))).expand() eq3 = diff(f(x), x, x) + 1/f(x)*(diff(f(x), x))**2 + 1/x*diff(f(x), x) eq4 = x*diff(f(x), x, x) + x/f(x)*diff(f(x), x)**2 + x*diff(f(x), x) eq5 = Eq((x*exp(f(x))).diff(x, x), 0) sol1 = Eq(f(x), log(x/(C1 + C2*x))) sol1a = Eq(C1 + C2/x - exp(-f(x)), 0) sol2 = sol1 sol3 = set( [Eq(f(x), -sqrt(C1 + C2*log(x))), Eq(f(x), sqrt(C1 + C2*log(x)))]) sol4 = set([Eq(f(x), sqrt(C1 + C2*exp(x))*exp(-x/2)), Eq(f(x), -sqrt(C1 + C2*exp(x))*exp(-x/2))]) sol5 = Eq(f(x), log(C1 + C2/x)) sol1s = constant_renumber(sol1) sol2s = constant_renumber(sol2) sol3s = constant_renumber(sol3) sol4s = constant_renumber(sol4) sol5s = constant_renumber(sol5) assert dsolve(eq1, hint=hint) in (sol1, sol1s) assert dsolve(eq1a, hint=hint) in (sol1, sol1s) assert dsolve(eq2, hint=hint) in (sol2, sol2s) assert set(dsolve(eq3, hint=hint)) in (sol3, sol3s) assert set(dsolve(eq4, hint=hint)) in (sol4, sol4s) assert dsolve(eq5, hint=hint) in (sol5, sol5s) assert checkodesol(eq1, sol1, order=2, solve_for_func=False)[0] assert checkodesol(eq1a, sol1a, order=2, solve_for_func=False)[0] assert checkodesol(eq2, sol2, order=2, solve_for_func=False)[0] assert checkodesol(eq3, sol3, order=2, solve_for_func=False) == {(True, 0)} assert checkodesol(eq4, sol4, order=2, solve_for_func=False) == {(True, 0)} assert checkodesol(eq5, sol5, order=2, solve_for_func=False)[0] not_Liouville1 = classify_ode(diff(f(x), x)/x + f(x)*diff(f(x), x, x)/2 - diff(f(x), x)**2/2, f(x)) not_Liouville2 = classify_ode(diff(f(x), x)/x + diff(f(x), x, x)/2 - x*diff(f(x), x)**2/2, f(x)) assert hint not in not_Liouville1 assert hint not in not_Liouville2 assert hint + '_Integral' not in not_Liouville1 assert hint + '_Integral' not in not_Liouville2 def test_unexpanded_Liouville_ODE(): # This is the same as eq1 from test_Liouville_ODE() above. eq1 = diff(f(x), x)/x + diff(f(x), x, x)/2 - diff(f(x), x)**2/2 eq2 = eq1*exp(-f(x))/exp(f(x)) sol2 = Eq(f(x), log(x/(C1 + C2*x))) sol2s = constant_renumber(sol2) assert dsolve(eq2) in (sol2, sol2s) assert checkodesol(eq2, sol2, order=2, solve_for_func=False)[0] def test_issue_4785(): from sympy.abc import A eq = x + A*(x + diff(f(x), x) + f(x)) + diff(f(x), x) + f(x) + 2 assert classify_ode(eq, f(x)) == ('1st_linear', 'almost_linear', '1st_power_series', 'lie_group', 'nth_linear_constant_coeff_undetermined_coefficients', 'nth_linear_constant_coeff_variation_of_parameters', '1st_linear_Integral', 'almost_linear_Integral', 'nth_linear_constant_coeff_variation_of_parameters_Integral') # issue 4864 eq = (x**2 + f(x)**2)*f(x).diff(x) - 2*x*f(x) assert classify_ode(eq, f(x)) == ('1st_exact', '1st_homogeneous_coeff_best', '1st_homogeneous_coeff_subs_indep_div_dep', '1st_homogeneous_coeff_subs_dep_div_indep', '1st_power_series', 'lie_group', '1st_exact_Integral', '1st_homogeneous_coeff_subs_indep_div_dep_Integral', '1st_homogeneous_coeff_subs_dep_div_indep_Integral') def test_issue_4825(): raises(ValueError, lambda: dsolve(f(x, y).diff(x) - y*f(x, y), f(x))) assert classify_ode(f(x, y).diff(x) - y*f(x, y), f(x), dict=True) == \ {'default': None, 'order': 0} # See also issue 3793, test Z13. raises(ValueError, lambda: dsolve(f(x).diff(x), f(y))) assert classify_ode(f(x).diff(x), f(y), dict=True) == \ {'default': None, 'order': 0} def test_constant_renumber_order_issue_5308(): from sympy.utilities.iterables import variations eq = f(x).diff(x) - y - x assert constant_renumber(C1*x + C2*y) == \ constant_renumber(C1*y + C2*x) == \ C1*x + C2*y e = C1*(C2 + x)*(C3 + y) for a, b, c in variations([C1, C2, C3], 3): assert constant_renumber(a*(b + x)*(c + y)) == e def test_issue_5770(): k = Symbol("k", real=True) t = Symbol('t') w = Function('w') sol = dsolve(w(t).diff(t, 6) - k**6*w(t), w(t)) assert len([s for s in sol.free_symbols if s.name.startswith('C')]) == 6 assert constantsimp((C1*cos(x) + C2*cos(x))*exp(x), set([C1, C2])) == \ C1*cos(x)*exp(x) assert constantsimp(C1*cos(x) + C2*cos(x) + C3*sin(x), set([C1, C2, C3])) == \ C1*cos(x) + C3*sin(x) assert constantsimp(exp(C1 + x), set([C1])) == C1*exp(x) assert constantsimp(x + C1 + y, set([C1, y])) == C1 + x assert constantsimp(x + C1 + Integral(x, (x, 1, 2)), set([C1])) == C1 + x def test_issue_5112_5430(): assert homogeneous_order(-log(x) + acosh(x), x) is None assert homogeneous_order(y - log(x), x, y) is None def test_nth_order_linear_euler_eq_homogeneous(): x, t, a, b, c = symbols('x t a b c') y = Function('y') our_hint = "nth_linear_euler_eq_homogeneous" eq = diff(f(t), t, 4)*t**4 - 13*diff(f(t), t, 2)*t**2 + 36*f(t) assert our_hint in classify_ode(eq) eq = a*y(t) + b*t*diff(y(t), t) + c*t**2*diff(y(t), t, 2) assert our_hint in classify_ode(eq) eq = Eq(-3*diff(f(x), x)*x + 2*x**2*diff(f(x), x, x), 0) sol = C1 + C2*x**Rational(5, 2) sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = Eq(3*f(x) - 5*diff(f(x), x)*x + 2*x**2*diff(f(x), x, x), 0) sol = C1*sqrt(x) + C2*x**3 sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = Eq(4*f(x) + 5*diff(f(x), x)*x + x**2*diff(f(x), x, x), 0) sol = (C1 + C2*log(x))/x**2 sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = Eq(6*f(x) - 6*diff(f(x), x)*x + 1*x**2*diff(f(x), x, x) + x**3*diff(f(x), x, x, x), 0) sol = dsolve(eq, f(x), hint=our_hint) sol = C1/x**2 + C2*x + C3*x**3 sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = Eq(-125*f(x) + 61*diff(f(x), x)*x - 12*x**2*diff(f(x), x, x) + x**3*diff(f(x), x, x, x), 0) sol = x**5*(C1 + C2*log(x) + C3*log(x)**2) sols = [sol, constant_renumber(sol)] sols += [sols[-1].expand()] assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs in sols assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = t**2*diff(y(t), t, 2) + t*diff(y(t), t) - 9*y(t) sol = C1*t**3 + C2*t**-3 sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, y(t), hint=our_hint).rhs in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = sin(x)*x**2*f(x).diff(x, 2) + sin(x)*x*f(x).diff(x) + sin(x)*f(x) sol = C1*sin(log(x)) + C2*cos(log(x)) sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] def test_nth_order_linear_euler_eq_nonhomogeneous_undetermined_coefficients(): x, t = symbols('x t') a, b, c, d = symbols('a b c d', integer=True) our_hint = "nth_linear_euler_eq_nonhomogeneous_undetermined_coefficients" eq = x**4*diff(f(x), x, 4) - 13*x**2*diff(f(x), x, 2) + 36*f(x) + x assert our_hint in classify_ode(eq, f(x)) eq = a*x**2*diff(f(x), x, 2) + b*x*diff(f(x), x) + c*f(x) + d*log(x) assert our_hint in classify_ode(eq, f(x)) eq = Eq(x**2*diff(f(x), x, x) + x*diff(f(x), x), 1) sol = C1 + C2*log(x) + log(x)**2/2 sols = constant_renumber(sol) assert our_hint in classify_ode(eq, f(x)) assert dsolve(eq, f(x), hint=our_hint).rhs in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = Eq(x**2*diff(f(x), x, x) - 2*x*diff(f(x), x) + 2*f(x), x**3) sol = x*(C1 + C2*x + Rational(1, 2)*x**2) sols = constant_renumber(sol) assert our_hint in classify_ode(eq, f(x)) assert dsolve(eq, f(x), hint=our_hint).rhs in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = Eq(x**2*diff(f(x), x, x) - x*diff(f(x), x) - 3*f(x), log(x)/x) sol = C1/x + C2*x**3 - Rational(1, 16)*log(x)/x - Rational(1, 8)*log(x)**2/x sols = constant_renumber(sol) assert our_hint in classify_ode(eq, f(x)) assert dsolve(eq, f(x), hint=our_hint).rhs.expand() in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = Eq(x**2*diff(f(x), x, x) + 3*x*diff(f(x), x) - 8*f(x), log(x)**3 - log(x)) sol = C1/x**4 + C2*x**2 - Rational(1,8)*log(x)**3 - Rational(3,32)*log(x)**2 - Rational(1,64)*log(x) - Rational(7, 256) sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs.expand() in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = Eq(x**3*diff(f(x), x, x, x) - 3*x**2*diff(f(x), x, x) + 6*x*diff(f(x), x) - 6*f(x), log(x)) sol = C1*x + C2*x**2 + C3*x**3 - Rational(1, 6)*log(x) - Rational(11, 36) sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs.expand() in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] def test_nth_order_linear_euler_eq_nonhomogeneous_variation_of_parameters(): x, t = symbols('x, t') a, b, c, d = symbols('a, b, c, d', integer=True) our_hint = "nth_linear_euler_eq_nonhomogeneous_variation_of_parameters" eq = Eq(x**2*diff(f(x),x,2) - 8*x*diff(f(x),x) + 12*f(x), x**2) assert our_hint in classify_ode(eq, f(x)) eq = Eq(a*x**3*diff(f(x),x,3) + b*x**2*diff(f(x),x,2) + c*x*diff(f(x),x) + d*f(x), x*log(x)) assert our_hint in classify_ode(eq, f(x)) eq = Eq(x**2*Derivative(f(x), x, x) - 2*x*Derivative(f(x), x) + 2*f(x), x**4) sol = C1*x + C2*x**2 + x**4/6 sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs.expand() in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = Eq(3*x**2*diff(f(x), x, x) + 6*x*diff(f(x), x) - 6*f(x), x**3*exp(x)) sol = C1/x**2 + C2*x + x*exp(x)/3 - 4*exp(x)/3 + 8*exp(x)/(3*x) - 8*exp(x)/(3*x**2) sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs.expand() in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = Eq(x**2*Derivative(f(x), x, x) - 2*x*Derivative(f(x), x) + 2*f(x), x**4*exp(x)) sol = C1*x + C2*x**2 + x**2*exp(x) - 2*x*exp(x) sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs.expand() in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = x**2*Derivative(f(x), x, x) - 2*x*Derivative(f(x), x) + 2*f(x) - log(x) sol = C1*x + C2*x**2 + log(x)/2 + S(3)/4 sols = constant_renumber(sol) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint).rhs in (sol, sols) assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] eq = -exp(x) + (x*Derivative(f(x), (x, 2)) + Derivative(f(x), x))/x sol = Eq(f(x), C1 + C2*log(x) + exp(x) - Ei(x)) assert our_hint in classify_ode(eq) assert dsolve(eq, f(x), hint=our_hint) == sol assert checkodesol(eq, sol, order=2, solve_for_func=False)[0] def test_issue_5095(): f = Function('f') raises(ValueError, lambda: dsolve(f(x).diff(x)**2, f(x), 'separable')) raises(ValueError, lambda: dsolve(f(x).diff(x)**2, f(x), 'fdsjf')) def test_almost_linear(): from sympy import Ei A = Symbol('A', positive=True) our_hint = 'almost_linear' f = Function('f') d = f(x).diff(x) eq = x**2*f(x)**2*d + f(x)**3 + 1 sol = dsolve(eq, f(x), hint = 'almost_linear') assert sol[0].rhs == (C1*exp(3/x) - 1)**(S(1)/3) assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] eq = x*f(x)*d + 2*x*f(x)**2 + 1 sol = dsolve(eq, f(x), hint = 'almost_linear') assert sol[0].rhs == -sqrt(C1 - 2*Ei(4*x))*exp(-2*x) assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] eq = x*d + x*f(x) + 1 sol = dsolve(eq, f(x), hint = 'almost_linear') assert sol.rhs == (C1 - Ei(x))*exp(-x) assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] assert our_hint in classify_ode(eq, f(x)) eq = x*exp(f(x))*d + exp(f(x)) + 3*x sol = dsolve(eq, f(x), hint = 'almost_linear') assert sol.rhs == log(C1/x - 3*x/2) assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] eq = x + A*(x + diff(f(x), x) + f(x)) + diff(f(x), x) + f(x) + 2 sol = dsolve(eq, f(x), hint = 'almost_linear') assert sol.rhs == (C1 + Piecewise( (x, Eq(A + 1, 0)), ((-A*x + A - x - 1)*exp(x)/(A + 1), True)))*exp(-x) assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] def test_exact_enhancement(): f = Function('f')(x) df = Derivative(f, x) eq = f/x**2 + ((f*x - 1)/x)*df sol = [Eq(f, (i*sqrt(C1*x**2 + 1) + 1)/x) for i in (-1, 1)] assert set(dsolve(eq, f)) == set(sol) assert checkodesol(eq, sol, order=1, solve_for_func=False) == [(True, 0), (True, 0)] eq = (x*f - 1) + df*(x**2 - x*f) sol = [Eq(f, x - sqrt(C1 + x**2 - 2*log(x))), Eq(f, x + sqrt(C1 + x**2 - 2*log(x)))] assert set(dsolve(eq, f)) == set(sol) assert checkodesol(eq, sol, order=1, solve_for_func=False) == [(True, 0), (True, 0)] eq = (x + 2)*sin(f) + df*x*cos(f) sol = [Eq(f, -asin(C1*exp(-x)/x**2) + pi), Eq(f, asin(C1*exp(-x)/x**2))] assert set(dsolve(eq, f)) == set(sol) assert checkodesol(eq, sol, order=1, solve_for_func=False) == [(True, 0), (True, 0)] @slow def test_separable_reduced(): f = Function('f') x = Symbol('x') df = f(x).diff(x) eq = (x / f(x))*df + tan(x**2*f(x) / (x**2*f(x) - 1)) assert classify_ode(eq) == ('separable_reduced', 'lie_group', 'separable_reduced_Integral') eq = x* df + f(x)* (1 / (x**2*f(x) - 1)) assert classify_ode(eq) == ('separable_reduced', 'lie_group', 'separable_reduced_Integral') sol = dsolve(eq, hint = 'separable_reduced', simplify=False) assert sol.lhs == log(x**2*f(x))/3 + log(x**2*f(x) - S(3)/2)/6 assert sol.rhs == C1 + log(x) assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] eq = f(x).diff(x) + (f(x) / (x**4*f(x) - x)) assert classify_ode(eq) == ('separable_reduced', 'lie_group', 'separable_reduced_Integral') sol = dsolve(eq, hint = 'separable_reduced') # FIXME: This one hangs #assert checkodesol(eq, sol, order=1, solve_for_func=False) == [(True, 0)] * 4 assert len(sol) == 4 eq = x*df + f(x)*(x**2*f(x)) sol = dsolve(eq, hint = 'separable_reduced', simplify=False) assert sol == Eq(log(x**2*f(x))/2 - log(x**2*f(x) - 2)/2, C1 + log(x)) assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] def test_homogeneous_function(): f = Function('f') eq1 = tan(x + f(x)) eq2 = sin((3*x)/(4*f(x))) eq3 = cos(3*x/4*f(x)) eq4 = log((3*x + 4*f(x))/(5*f(x) + 7*x)) eq5 = exp((2*x**2)/(3*f(x)**2)) eq6 = log((3*x + 4*f(x))/(5*f(x) + 7*x) + exp((2*x**2)/(3*f(x)**2))) eq7 = sin((3*x)/(5*f(x) + x**2)) assert homogeneous_order(eq1, x, f(x)) == None assert homogeneous_order(eq2, x, f(x)) == 0 assert homogeneous_order(eq3, x, f(x)) == None assert homogeneous_order(eq4, x, f(x)) == 0 assert homogeneous_order(eq5, x, f(x)) == 0 assert homogeneous_order(eq6, x, f(x)) == 0 assert homogeneous_order(eq7, x, f(x)) == None def test_linear_coeff_match(): from sympy.solvers.ode import _linear_coeff_match n, d = z*(2*x + 3*f(x) + 5), z*(7*x + 9*f(x) + 11) rat = n/d eq1 = sin(rat) + cos(rat.expand()) eq2 = rat eq3 = log(sin(rat)) ans = (4, -S(13)/3) assert _linear_coeff_match(eq1, f(x)) == ans assert _linear_coeff_match(eq2, f(x)) == ans assert _linear_coeff_match(eq3, f(x)) == ans # no c eq4 = (3*x)/f(x) # not x and f(x) eq5 = (3*x + 2)/x # denom will be zero eq6 = (3*x + 2*f(x) + 1)/(3*x + 2*f(x) + 5) # not rational coefficient eq7 = (3*x + 2*f(x) + sqrt(2))/(3*x + 2*f(x) + 5) assert _linear_coeff_match(eq4, f(x)) is None assert _linear_coeff_match(eq5, f(x)) is None assert _linear_coeff_match(eq6, f(x)) is None assert _linear_coeff_match(eq7, f(x)) is None def test_linear_coefficients(): f = Function('f') sol = Eq(f(x), C1/(x**2 + 6*x + 9) - S(3)/2) eq = f(x).diff(x) + (3 + 2*f(x))/(x + 3) assert dsolve(eq, hint='linear_coefficients') == sol assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] def test_constantsimp_take_problem(): c = exp(C1) + 2 assert len(Poly(constantsimp(exp(C1) + c + c*x, [C1])).gens) == 2 def test_issue_6879(): f = Function('f') eq = Eq(Derivative(f(x), x, 2) - 2*Derivative(f(x), x) + f(x), sin(x)) sol = (C1 + C2*x)*exp(x) + cos(x)/2 assert dsolve(eq).rhs == sol assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] def test_issue_6989(): f = Function('f') k = Symbol('k') eq = f(x).diff(x) - x*exp(-k*x) sol = Eq(f(x), C1 + Piecewise( ((-k*x - 1)*exp(-k*x)/k**2, Ne(k**2, 0)), (x**2/2, True) )) assert dsolve(eq, f(x)) == sol assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] eq = -f(x).diff(x) + x*exp(-k*x) sol = Eq(f(x), C1 + Piecewise( ((-k*x - 1)*exp(-k*x)/k**2, Ne(k**2, 0)), (+x**2/2, True) )) assert dsolve(eq, f(x)) == sol assert checkodesol(eq, sol, order=1, solve_for_func=False)[0] def test_heuristic1(): y, a, b, c, a4, a3, a2, a1, a0 = symbols("y a b c a4 a3 a2 a1 a0") y = Symbol('y') f = Function('f') xi = Function('xi') eta = Function('eta') df = f(x).diff(x) eq = Eq(df, x**2*f(x)) eq1 = f(x).diff(x) + a*f(x) - c*exp(b*x) eq2 = f(x).diff(x) + 2*x*f(x) - x*exp(-x**2) eq3 = (1 + 2*x)*df + 2 - 4*exp(-f(x)) eq4 = f(x).diff(x) - (a4*x**4 + a3*x**3 + a2*x**2 + a1*x + a0)**(S(-1)/2) eq5 = x**2*df - f(x) + x**2*exp(x - (1/x)) eqlist = [eq, eq1, eq2, eq3, eq4, eq5] i = infinitesimals(eq, hint='abaco1_simple') assert i == [{eta(x, f(x)): exp(x**3/3), xi(x, f(x)): 0}, {eta(x, f(x)): f(x), xi(x, f(x)): 0}, {eta(x, f(x)): 0, xi(x, f(x)): x**(-2)}] i1 = infinitesimals(eq1, hint='abaco1_simple') assert i1 == [{eta(x, f(x)): exp(-a*x), xi(x, f(x)): 0}] i2 = infinitesimals(eq2, hint='abaco1_simple') assert i2 == [{eta(x, f(x)): exp(-x**2), xi(x, f(x)): 0}] i3 = infinitesimals(eq3, hint='abaco1_simple') assert i3 == [{eta(x, f(x)): 0, xi(x, f(x)): 2*x + 1}, {eta(x, f(x)): 0, xi(x, f(x)): 1/(exp(f(x)) - 2)}] i4 = infinitesimals(eq4, hint='abaco1_simple') assert i4 == [{eta(x, f(x)): 1, xi(x, f(x)): 0}, {eta(x, f(x)): 0, xi(x, f(x)): sqrt(a0 + a1*x + a2*x**2 + a3*x**3 + a4*x**4)}] i5 = infinitesimals(eq5, hint='abaco1_simple') assert i5 == [{xi(x, f(x)): 0, eta(x, f(x)): exp(-1/x)}] ilist = [i, i1, i2, i3, i4, i5] for eq, i in (zip(eqlist, ilist)): check = checkinfsol(eq, i) assert check[0] def test_issue_6247(): eq = x**2*f(x)**2 + x*Derivative(f(x), x) sol = Eq(f(x), 2*C1/(C1*x**2 - 1)) assert dsolve(eq, hint = 'separable_reduced') == sol assert checkodesol(eq, sol, order=1)[0] eq = f(x).diff(x, x) + 4*f(x) sol = Eq(f(x), C1*sin(2*x) + C2*cos(2*x)) assert dsolve(eq) == sol assert checkodesol(eq, sol, order=1)[0] def test_heuristic2(): y = Symbol('y') xi = Function('xi') eta = Function('eta') df = f(x).diff(x) # This ODE can be solved by the Lie Group method, when there are # better assumptions eq = df - (f(x)/x)*(x*log(x**2/f(x)) + 2) i = infinitesimals(eq, hint='abaco1_product') assert i == [{eta(x, f(x)): f(x)*exp(-x), xi(x, f(x)): 0}] assert checkinfsol(eq, i)[0] @slow def test_heuristic3(): y = Symbol('y') xi = Function('xi') eta = Function('eta') a, b = symbols("a b") df = f(x).diff(x) eq = x**2*df + x*f(x) + f(x)**2 + x**2 i = infinitesimals(eq, hint='bivariate') assert i == [{eta(x, f(x)): f(x), xi(x, f(x)): x}] assert checkinfsol(eq, i)[0] eq = x**2*(-f(x)**2 + df)- a*x**2*f(x) + 2 - a*x i = infinitesimals(eq, hint='bivariate') assert checkinfsol(eq, i)[0] def test_heuristic_4(): y, a = symbols("y a") xi = Function('xi') eta = Function('eta') eq = x*(f(x).diff(x)) + 1 - f(x)**2 i = infinitesimals(eq, hint='chi') assert checkinfsol(eq, i)[0] def test_heuristic_function_sum(): xi = Function('xi') eta = Function('eta') eq = f(x).diff(x) - (3*(1 + x**2/f(x)**2)*atan(f(x)/x) + (1 - 2*f(x))/x + (1 - 3*f(x))*(x/f(x)**2)) i = infinitesimals(eq, hint='function_sum') assert i == [{eta(x, f(x)): f(x)**(-2) + x**(-2), xi(x, f(x)): 0}] assert checkinfsol(eq, i)[0] def test_heuristic_abaco2_similar(): xi = Function('xi') eta = Function('eta') F = Function('F') a, b = symbols("a b") eq = f(x).diff(x) - F(a*x + b*f(x)) i = infinitesimals(eq, hint='abaco2_similar') assert i == [{eta(x, f(x)): -a/b, xi(x, f(x)): 1}] assert checkinfsol(eq, i)[0] eq = f(x).diff(x) - (f(x)**2 / (sin(f(x) - x) - x**2 + 2*x*f(x))) i = infinitesimals(eq, hint='abaco2_similar') assert i == [{eta(x, f(x)): f(x)**2, xi(x, f(x)): f(x)**2}] assert checkinfsol(eq, i)[0] def test_heuristic_abaco2_unique_unknown(): xi = Function('xi') eta = Function('eta') F = Function('F') a, b = symbols("a b") x = Symbol("x", positive=True) eq = f(x).diff(x) - x**(a - 1)*(f(x)**(1 - b))*F(x**a/a + f(x)**b/b) i = infinitesimals(eq, hint='abaco2_unique_unknown') assert i == [{eta(x, f(x)): -f(x)*f(x)**(-b), xi(x, f(x)): x*x**(-a)}] assert checkinfsol(eq, i)[0] eq = f(x).diff(x) + tan(F(x**2 + f(x)**2) + atan(x/f(x))) i = infinitesimals(eq, hint='abaco2_unique_unknown') assert i == [{eta(x, f(x)): x, xi(x, f(x)): -f(x)}] assert checkinfsol(eq, i)[0] eq = (x*f(x).diff(x) + f(x) + 2*x)**2 -4*x*f(x) -4*x**2 -4*a i = infinitesimals(eq, hint='abaco2_unique_unknown') assert checkinfsol(eq, i)[0] def test_heuristic_linear(): xi = Function('xi') eta = Function('eta') F = Function('F') a, b, m, n = symbols("a b m n") eq = x**(n*(m + 1) - m)*(f(x).diff(x)) - a*f(x)**n -b*x**(n*(m + 1)) i = infinitesimals(eq, hint='linear') assert checkinfsol(eq, i)[0] @XFAIL def test_kamke(): a, b, alpha, c = symbols("a b alpha c") eq = x**2*(a*f(x)**2+(f(x).diff(x))) + b*x**alpha + c i = infinitesimals(eq, hint='sum_function') assert checkinfsol(eq, i)[0] def test_series(): # FIXME: Maybe there should be a way to check series solutions # checkodesol doesn't work with them. C1 = Symbol("C1") eq = f(x).diff(x) - f(x) assert dsolve(eq, hint='1st_power_series') == Eq(f(x), C1 + C1*x + C1*x**2/2 + C1*x**3/6 + C1*x**4/24 + C1*x**5/120 + O(x**6)) eq = f(x).diff(x) - x*f(x) assert dsolve(eq, hint='1st_power_series') == Eq(f(x), C1*x**4/8 + C1*x**2/2 + C1 + O(x**6)) eq = f(x).diff(x) - sin(x*f(x)) sol = Eq(f(x), (x - 2)**2*(1+ sin(4))*cos(4) + (x - 2)*sin(4) + 2 + O(x**3)) assert dsolve(eq, hint='1st_power_series', ics={f(2): 2}, n=3) == sol @slow def test_lie_group(): C1 = Symbol("C1") x = Symbol("x") # assuming x is real generates an error! a, b, c = symbols("a b c") eq = f(x).diff(x)**2 sol = dsolve(eq, f(x), hint='lie_group') assert checkodesol(eq, sol)[0] eq = Eq(f(x).diff(x), x**2*f(x)) sol = dsolve(eq, f(x), hint='lie_group') assert sol == Eq(f(x), C1*exp(x**3)**(S(1)/3)) assert checkodesol(eq, sol)[0] eq = f(x).diff(x) + a*f(x) - c*exp(b*x) sol = dsolve(eq, f(x), hint='lie_group') assert checkodesol(eq, sol)[0] eq = f(x).diff(x) + 2*x*f(x) - x*exp(-x**2) sol = dsolve(eq, f(x), hint='lie_group') actual_sol = Eq(f(x), (C1 + x**2/2)*exp(-x**2)) errstr = str(eq)+' : '+str(sol)+' == '+str(actual_sol) assert sol == actual_sol, errstr assert checkodesol(eq, sol)[0] eq = (1 + 2*x)*(f(x).diff(x)) + 2 - 4*exp(-f(x)) sol = dsolve(eq, f(x), hint='lie_group') assert sol == Eq(f(x), log(C1/(2*x + 1) + 2)) assert checkodesol(eq, sol)[0] eq = x**2*(f(x).diff(x)) - f(x) + x**2*exp(x - (1/x)) sol = dsolve(eq, f(x), hint='lie_group') assert checkodesol(eq, sol)[0] eq = x**2*f(x)**2 + x*Derivative(f(x), x) sol = dsolve(eq, f(x), hint='lie_group') assert sol == Eq(f(x), 2/(C1 + x**2)) assert checkodesol(eq, sol)[0] @XFAIL def test_lie_group_issue15219(): eqn = exp(f(x).diff(x)-f(x)) assert 'lie_group' not in classify_ode(eqn, f(x)) def test_user_infinitesimals(): x = Symbol("x") # assuming x is real generates an error eq = x*(f(x).diff(x)) + 1 - f(x)**2 sol = Eq(f(x), (C1 + x**2)/(C1 - x**2)) infinitesimals = {'xi':sqrt(f(x) - 1)/sqrt(f(x) + 1), 'eta':0} assert dsolve(eq, hint='lie_group', **infinitesimals) == sol assert checkodesol(eq, sol) == (True, 0) raises(ValueError, lambda: dsolve(eq, hint='lie_group', xi=0, eta=f(x))) def test_issue_7081(): eq = x*(f(x).diff(x)) + 1 - f(x)**2 s = Eq(f(x), -1/(-C1 + x**2)*(C1 + x**2)) assert dsolve(eq) == s assert checkodesol(eq, s) == (True, 0) @slow def test_2nd_power_series_ordinary(): # FIXME: Maybe there should be a way to check series solutions # checkodesol doesn't work with them. C1, C2 = symbols("C1 C2") eq = f(x).diff(x, 2) - x*f(x) assert classify_ode(eq) == ('2nd_power_series_ordinary',) assert dsolve(eq) == Eq(f(x), C2*(x**3/6 + 1) + C1*x*(x**3/12 + 1) + O(x**6)) assert dsolve(eq, x0=-2) == Eq(f(x), C2*((x + 2)**4/6 + (x + 2)**3/6 - (x + 2)**2 + 1) + C1*(x + (x + 2)**4/12 - (x + 2)**3/3 + S(2)) + O(x**6)) assert dsolve(eq, n=2) == Eq(f(x), C2*x + C1 + O(x**2)) eq = (1 + x**2)*(f(x).diff(x, 2)) + 2*x*(f(x).diff(x)) -2*f(x) assert classify_ode(eq) == ('2nd_power_series_ordinary',) assert dsolve(eq) == Eq(f(x), C2*(-x**4/3 + x**2 + 1) + C1*x + O(x**6)) eq = f(x).diff(x, 2) + x*(f(x).diff(x)) + f(x) assert classify_ode(eq) == ('2nd_power_series_ordinary',) assert dsolve(eq) == Eq(f(x), C2*( x**4/8 - x**2/2 + 1) + C1*x*(-x**2/3 + 1) + O(x**6)) eq = f(x).diff(x, 2) + f(x).diff(x) - x*f(x) assert classify_ode(eq) == ('2nd_power_series_ordinary',) assert dsolve(eq) == Eq(f(x), C2*( -x**4/24 + x**3/6 + 1) + C1*x*(x**3/24 + x**2/6 - x/2 + 1) + O(x**6)) eq = f(x).diff(x, 2) + x*f(x) assert classify_ode(eq) == ('2nd_power_series_ordinary',) assert dsolve(eq, n=7) == Eq(f(x), C2*( x**6/180 - x**3/6 + 1) + C1*x*(-x**3/12 + 1) + O(x**7)) def test_2nd_power_series_regular(): # FIXME: Maybe there should be a way to check series solutions # checkodesol doesn't work with them. C1, C2 = symbols("C1 C2") eq = x**2*(f(x).diff(x, 2)) - 3*x*(f(x).diff(x)) + (4*x + 4)*f(x) assert dsolve(eq) == Eq(f(x), C1*x**2*(-16*x**3/9 + 4*x**2 - 4*x + 1) + O(x**6)) eq = 4*x**2*(f(x).diff(x, 2)) -8*x**2*(f(x).diff(x)) + (4*x**2 + 1)*f(x) assert dsolve(eq) == Eq(f(x), C1*sqrt(x)*( x**4/24 + x**3/6 + x**2/2 + x + 1) + O(x**6)) eq = x**2*(f(x).diff(x, 2)) - x**2*(f(x).diff(x)) + ( x**2 - 2)*f(x) assert dsolve(eq) == Eq(f(x), C1*(-x**6/720 - 3*x**5/80 - x**4/8 + x**2/2 + x/2 + 1)/x + C2*x**2*(-x**3/60 + x**2/20 + x/2 + 1) + O(x**6)) eq = x**2*(f(x).diff(x, 2)) + x*(f(x).diff(x)) + (x**2 - S(1)/4)*f(x) assert dsolve(eq) == Eq(f(x), C1*(x**4/24 - x**2/2 + 1)/sqrt(x) + C2*sqrt(x)*(x**4/120 - x**2/6 + 1) + O(x**6)) eq = x*(f(x).diff(x, 2)) - f(x).diff(x) + 4*x**3*f(x) assert dsolve(eq) == Eq(f(x), C2*(-x**4/2 + 1) + C1*x**2 + O(x**6)) def test_issue_7093(): x = Symbol("x") # assuming x is real leads to an error sol = [Eq(f(x), C1 - 2*x*sqrt(x**3)/5), Eq(f(x), C1 + 2*x*sqrt(x**3)/5)] eq = Derivative(f(x), x)**2 - x**3 assert set(dsolve(eq)) == set(sol) assert checkodesol(eq, sol) == [(True, 0)] * 2 def test_dsolve_linsystem_symbol(): eps = Symbol('epsilon', positive=True) eq1 = (Eq(diff(f(x), x), -eps*g(x)), Eq(diff(g(x), x), eps*f(x))) sol1 = [Eq(f(x), -C1*eps*cos(eps*x) - C2*eps*sin(eps*x)), Eq(g(x), -C1*eps*sin(eps*x) + C2*eps*cos(eps*x))] assert checksysodesol(eq1, sol1) == (True, [0, 0]) def test_C1_function_9239(): t = Symbol('t') C1 = Function('C1') C2 = Function('C2') C3 = Symbol('C3') C4 = Symbol('C4') eq = (Eq(diff(C1(t), t), 9*C2(t)), Eq(diff(C2(t), t), 12*C1(t))) sol = [Eq(C1(t), 9*C3*exp(6*sqrt(3)*t) + 9*C4*exp(-6*sqrt(3)*t)), Eq(C2(t), 6*sqrt(3)*C3*exp(6*sqrt(3)*t) - 6*sqrt(3)*C4*exp(-6*sqrt(3)*t))] assert checksysodesol(eq, sol) == (True, [0, 0]) def test_issue_15056(): t = Symbol('t') C3 = Symbol('C3') assert get_numbered_constants(Symbol('C1') * Function('C2')(t)) == C3 def test_issue_10379(): t,y = symbols('t,y') eq = f(t).diff(t)-(1-51.05*y*f(t)) sol = Eq(f(t), (0.019588638589618*exp(y*(C1 - 51.05*t)) + 0.019588638589618)/y) dsolve_sol = dsolve(eq, rational=False) assert str(dsolve_sol) == str(sol) assert checkodesol(eq, dsolve_sol)[0] def test_issue_10867(): x = Symbol('x') eq = Eq(g(x).diff(x).diff(x), (x-2)**2 + (x-3)**3) sol = Eq(g(x), C1 + C2*x + x**5/20 - 2*x**4/3 + 23*x**3/6 - 23*x**2/2) assert dsolve(eq, g(x)) == sol assert checkodesol(eq, sol, order=2, solve_for_func=False) == (True, 0) def test_issue_11290(): eq = cos(f(x)) - (x*sin(f(x)) - f(x)**2)*f(x).diff(x) sol_1 = dsolve(eq, f(x), simplify=False, hint='1st_exact_Integral') sol_0 = dsolve(eq, f(x), simplify=False, hint='1st_exact') assert sol_1.dummy_eq(Eq(Subs( Integral(u**2 - x*sin(u) - Integral(-sin(u), x), u) + Integral(cos(u), x), u, f(x)), C1)) assert sol_1.doit() == sol_0 assert checkodesol(eq, sol_0, order=1, solve_for_func=False) assert checkodesol(eq, sol_1, order=1, solve_for_func=False) def test_issue_4838(): # Issue #15999 eq = f(x).diff(x) - C1*f(x) sol = Eq(f(x), C2*exp(C1*x)) assert dsolve(eq, f(x)) == sol assert checkodesol(eq, sol, order=1, solve_for_func=False) == (True, 0) # Issue #13691 eq = f(x).diff(x) - C1*g(x).diff(x) sol = Eq(f(x), C2 + C1*g(x)) assert dsolve(eq, f(x)) == sol assert checkodesol(eq, sol, f(x), order=1, solve_for_func=False) == (True, 0) # Issue #4838 eq = f(x).diff(x) - 3*C1 - 3*x**2 sol = Eq(f(x), C2 + 3*C1*x + x**3) assert dsolve(eq, f(x)) == sol assert checkodesol(eq, sol, order=1, solve_for_func=False) == (True, 0) @slow def test_issue_14395(): eq = Derivative(f(x), x, x) + 9*f(x) - sec(x) sol = Eq(f(x), (C1 - x/3 + sin(2*x)/3)*sin(3*x) + (C2 + log(cos(x)) - 2*log(cos(x)**2)/3 + 2*cos(x)**2/3)*cos(3*x)) assert dsolve(eq, f(x)) == sol # FIXME: assert checkodesol(eq, sol, order=2, solve_for_func=False) == (True, 0) def test_sysode_linear_neq_order1(): from sympy.abc import t Z0 = Function('Z0') Z1 = Function('Z1') Z2 = Function('Z2') Z3 = Function('Z3') k01, k10, k20, k21, k23, k30 = symbols('k01 k10 k20 k21 k23 k30') eq = (Eq(Derivative(Z0(t), t), -k01*Z0(t) + k10*Z1(t) + k20*Z2(t) + k30*Z3(t)), Eq(Derivative(Z1(t), t), k01*Z0(t) - k10*Z1(t) + k21*Z2(t)), Eq(Derivative(Z2(t), t), -(k20 + k21 + k23)*Z2(t)), Eq(Derivative(Z3(t), t), k23*Z2(t) - k30*Z3(t))) sols_eq = [Eq(Z0(t), C1*k10/k01 + C2*(-k10 + k30)*exp(-k30*t)/(k01 + k10 - k30) - C3*exp(t*(- k01 - k10)) + C4*(k10*k20 + k10*k21 - k10*k30 - k20**2 - k20*k21 - k20*k23 + k20*k30 + k23*k30)*exp(t*(-k20 - k21 - k23))/(k23*(k01 + k10 - k20 - k21 - k23))), Eq(Z1(t), C1 - C2*k01*exp(-k30*t)/(k01 + k10 - k30) + C3*exp(t*(-k01 - k10)) + C4*(k01*k20 + k01*k21 - k01*k30 - k20*k21 - k21**2 - k21*k23 + k21*k30)*exp(t*(-k20 - k21 - k23))/(k23*(k01 + k10 - k20 - k21 - k23))), Eq(Z2(t), C4*(-k20 - k21 - k23 + k30)*exp(t*(-k20 - k21 - k23))/k23), Eq(Z3(t), C2*exp(-k30*t) + C4*exp(t*(-k20 - k21 - k23)))] assert dsolve(eq, simplify=False) == sols_eq assert checksysodesol(eq, sols_eq) == (True, [0, 0, 0, 0]) def test_nth_order_reducible(): from sympy.solvers.ode import _nth_order_reducible_match eqn = Eq(x*Derivative(f(x), x)**2 + Derivative(f(x), x, 2)) sol = Eq(f(x), C1 - sqrt(-1/C2)*log(-C2*sqrt(-1/C2) + x) + sqrt(-1/C2)*log(C2*sqrt(-1/C2) + x)) assert checkodesol(eqn, sol, order=2, solve_for_func=False) == (True, 0) assert sol == dsolve(eqn, f(x), hint='nth_order_reducible') assert sol == dsolve(eqn, f(x)) F = lambda eq: _nth_order_reducible_match(eq, f(x)) D = Derivative assert F(D(y*f(x), x, y) + D(f(x), x)) is None assert F(D(y*f(y), y, y) + D(f(y), y)) is None assert F(f(x)*D(f(x), x) + D(f(x), x, 2)) is None assert F(D(x*f(y), y, 2) + D(u*y*f(x), x, 3)) is None # no simplification by design assert F(D(f(y), y, 2) + D(f(y), y, 3) + D(f(x), x, 4)) is None assert F(D(f(x), x, 2) + D(f(x), x, 3)) == dict(n=2) eqn = -exp(x) + (x*Derivative(f(x), (x, 2)) + Derivative(f(x), x))/x sol = Eq(f(x), C1 + C2*log(x) + exp(x) - Ei(x)) assert checkodesol(eqn, sol, order=2, solve_for_func=False) == (True, 0) assert sol == dsolve(eqn, f(x)) assert sol == dsolve(eqn, f(x), hint='nth_order_reducible') eqn = Eq(sqrt(2) * f(x).diff(x,x,x) + f(x).diff(x), 0) sol = Eq(f(x), C1 + C2*sin(2**(S(3)/4)*x/2) + C3*cos(2**(S(3)/4)*x/2)) assert checkodesol(eqn, sol, order=2, solve_for_func=False) == (True, 0) assert sol == dsolve(eqn, f(x)) assert sol == dsolve(eqn, f(x), hint='nth_order_reducible') eqn = f(x).diff(x, 2) + 2*f(x).diff(x) sol = Eq(f(x), C1 + C2*exp(-2*x)) sols = constant_renumber(sol) assert checkodesol(eqn, sol, order=2, solve_for_func=False) == (True, 0) assert dsolve(eqn, f(x)) in (sol, sols) assert dsolve(eqn, f(x), hint='nth_order_reducible') in (sol, sols) eqn = f(x).diff(x, 3) + f(x).diff(x, 2) - 6*f(x).diff(x) sol = Eq(f(x), C1 + C2*exp(-3*x) + C3*exp(2*x)) sols = constant_renumber(sol) assert checkodesol(eqn, sol, order=2, solve_for_func=False) == (True, 0) assert dsolve(eqn, f(x)) in (sol, sols) assert dsolve(eqn, f(x), hint='nth_order_reducible') in (sol, sols) eqn = f(x).diff(x, 4) - f(x).diff(x, 3) - 4*f(x).diff(x, 2) + \ 4*f(x).diff(x) sol = Eq(f(x), C1 + C2*exp(x) + C3*exp(-2*x) + C4*exp(2*x)) sols = constant_renumber(sol) assert checkodesol(eqn, sol, order=2, solve_for_func=False) == (True, 0) assert dsolve(eqn, f(x)) in (sol, sols) assert dsolve(eqn, f(x), hint='nth_order_reducible') in (sol, sols) eqn = f(x).diff(x, 4) + 3*f(x).diff(x, 3) sol = Eq(f(x), C1 + C2*x + C3*x**2 + C4*exp(-3*x)) sols = constant_renumber(sol) assert checkodesol(eqn, sol, order=2, solve_for_func=False) == (True, 0) assert dsolve(eqn, f(x)) in (sol, sols) assert dsolve(eqn, f(x), hint='nth_order_reducible') in (sol, sols) eqn = f(x).diff(x, 4) - 2*f(x).diff(x, 2) sol = Eq(f(x), C1 + C2*x + C3*exp(x*sqrt(2)) + C4*exp(-x*sqrt(2))) sols = constant_renumber(sol) assert checkodesol(eqn, sol, order=2, solve_for_func=False) == (True, 0) assert dsolve(eqn, f(x)) in (sol, sols) assert dsolve(eqn, f(x), hint='nth_order_reducible') in (sol, sols) eqn = f(x).diff(x, 4) + 4*f(x).diff(x, 2) sol = Eq(f(x), C1 + C2*sin(2*x) + C3*cos(2*x) + C4*x) sols = constant_renumber(sol) assert checkodesol(eqn, sol, order=2, solve_for_func=False) == (True, 0) assert dsolve(eqn, f(x)) in (sol, sols) assert dsolve(eqn, f(x), hint='nth_order_reducible') in (sol, sols) eqn = f(x).diff(x, 5) + 2*f(x).diff(x, 3) + f(x).diff(x) # These are equivalent: sol1 = Eq(f(x), C1 + (C2 + C3*x)*sin(x) + (C4 + C5*x)*cos(x)) sol2 = Eq(f(x), C1 + C2*(x*sin(x) + cos(x)) + C3*(-x*cos(x) + sin(x)) + C4*sin(x) + C5*cos(x)) sol1s = constant_renumber(sol1) sol2s = constant_renumber(sol2) assert checkodesol(eqn, sol1, order=2, solve_for_func=False) == (True, 0) assert checkodesol(eqn, sol2, order=2, solve_for_func=False) == (True, 0) assert dsolve(eqn, f(x)) in (sol1, sol1s) assert dsolve(eqn, f(x), hint='nth_order_reducible') in (sol2, sol2s) # In this case the reduced ODE has two distinct solutions eqn = f(x).diff(x, 2) - f(x).diff(x)**3 sol = [Eq(f(x), C2 - sqrt(2)*I*(C1 + x)*sqrt(1/(C1 + x))), Eq(f(x), C2 + sqrt(2)*I*(C1 + x)*sqrt(1/(C1 + x)))] sols = constant_renumber(sol) assert checkodesol(eqn, sol, order=2, solve_for_func=False) == [(True, 0), (True, 0)] assert dsolve(eqn, f(x)) in (sol, sols) assert dsolve(eqn, f(x), hint='nth_order_reducible') in (sol, sols) def test_nth_algebraic(): eqn = Eq(Derivative(f(x), x), Derivative(g(x), x)) sol = Eq(f(x), C1 + g(x)) assert checkodesol(eqn, sol, order=1, solve_for_func=False)[0] assert sol == dsolve(eqn, f(x), hint='nth_algebraic') assert sol == dsolve(eqn, f(x)) eqn = (diff(f(x)) - x)*(diff(f(x)) + x) sol = [Eq(f(x), C1 - x**2/2), Eq(f(x), C1 + x**2/2)] assert checkodesol(eqn, sol, order=1, solve_for_func=False)[0] assert sol == dsolve(eqn, f(x), hint='nth_algebraic') assert sol == dsolve(eqn, f(x)) eqn = (1 - sin(f(x))) * f(x).diff(x) sol = Eq(f(x), C1) assert checkodesol(eqn, sol, order=1, solve_for_func=False)[0] assert sol == dsolve(eqn, f(x), hint='nth_algebraic') assert sol == dsolve(eqn, f(x)) M, m, r, t = symbols('M m r t') phi = Function('phi') eqn = Eq(-M * phi(t).diff(t), Rational(3, 2) * m * r**2 * phi(t).diff(t) * phi(t).diff(t,t)) solns = [Eq(phi(t), C1), Eq(phi(t), C1 + C2*t - M*t**2/(3*m*r**2))] assert checkodesol(eqn, solns[0], order=2, solve_for_func=False)[0] assert checkodesol(eqn, solns[1], order=2, solve_for_func=False)[0] assert set(solns) == set(dsolve(eqn, phi(t), hint='nth_algebraic')) assert set(solns) == set(dsolve(eqn, phi(t))) eqn = f(x) * f(x).diff(x) * f(x).diff(x, x) sol = Eq(f(x), C1 + C2*x) assert checkodesol(eqn, sol, order=1, solve_for_func=False)[0] assert sol == dsolve(eqn, f(x), hint='nth_algebraic') assert sol == dsolve(eqn, f(x)) eqn = f(x) * f(x).diff(x) * f(x).diff(x, x) * (f(x) - 1) sol = Eq(f(x), C1 + C2*x) assert checkodesol(eqn, sol, order=1, solve_for_func=False)[0] assert sol == dsolve(eqn, f(x), hint='nth_algebraic') assert sol == dsolve(eqn, f(x)) eqn = f(x) * f(x).diff(x) * f(x).diff(x, x) * (f(x) - 1) * (f(x).diff(x) - x) solns = [Eq(f(x), C1 + x**2/2), Eq(f(x), C1 + C2*x)] assert checkodesol(eqn, solns[0], order=2, solve_for_func=False)[0] assert checkodesol(eqn, solns[1], order=2, solve_for_func=False)[0] assert set(solns) == set(dsolve(eqn, f(x), hint='nth_algebraic')) assert set(solns) == set(dsolve(eqn, f(x))) def test_nth_algebraic_issue15999(): eqn = f(x).diff(x) - C1 sol = Eq(f(x), C1*x + C2) # Correct solution assert checkodesol(eqn, sol, order=1, solve_for_func=False) == (True, 0) assert dsolve(eqn, f(x), hint='nth_algebraic') == sol assert dsolve(eqn, f(x)) == sol def test_nth_algebraic_redundant_solutions(): # This one has a redundant solution that should be removed eqn = f(x)*f(x).diff(x) soln = Eq(f(x), C1) assert checkodesol(eqn, soln, order=1, solve_for_func=False)[0] assert soln == dsolve(eqn, f(x), hint='nth_algebraic') assert soln == dsolve(eqn, f(x)) # This has two integral solutions and no algebraic solutions eqn = (diff(f(x)) - x)*(diff(f(x)) + x) sol = [Eq(f(x), C1 - x**2/2), Eq(f(x), C1 + x**2/2)] assert all(c[0] for c in checkodesol(eqn, sol, order=1, solve_for_func=False)) assert set(sol) == set(dsolve(eqn, f(x), hint='nth_algebraic')) assert set(sol) == set(dsolve(eqn, f(x))) # This one doesn't work with dsolve at the time of writing but the # redundancy checking code should not remove the algebraic solution. from sympy.solvers.ode import _nth_algebraic_remove_redundant_solutions eqn = f(x) + f(x)*f(x).diff(x) solns = [Eq(f(x), 0), Eq(f(x), C1 - x)] solns_final = _nth_algebraic_remove_redundant_solutions(eqn, solns, 1, x) assert all(c[0] for c in checkodesol(eqn, solns, order=1, solve_for_func=False)) assert set(solns) == set(solns_final) solns = [Eq(f(x), exp(x)), Eq(f(x), C1*exp(C2*x))] solns_final = _nth_algebraic_remove_redundant_solutions(eqn, solns, 2, x) assert solns_final == [Eq(f(x), C1*exp(C2*x))] # This one needs a substitution f' = g. eqn = -exp(x) + (x*Derivative(f(x), (x, 2)) + Derivative(f(x), x))/x sol = Eq(f(x), C1 + C2*log(x) + exp(x) - Ei(x)) assert checkodesol(eqn, sol, order=2, solve_for_func=False)[0] assert sol == dsolve(eqn, f(x)) # # These tests can be combined with the above test if they get fixed # so that dsolve actually works in all these cases. # # Fails due to division by f(x) eliminating the solution before nth_algebraic # is called. @XFAIL def test_nth_algebraic_find_multiple1(): eqn = f(x) + f(x)*f(x).diff(x) solns = [Eq(f(x), 0), Eq(f(x), C1 - x)] assert all(c[0] for c in checkodesol(eqn, solns, order=1, solve_for_func=False)) assert set(solns) == set(dsolve(eqn, f(x))) # prep = True breaks this def test_nth_algebraic_noprep1(): eqn = Derivative(x*f(x), x, x, x) sol = Eq(f(x), (C1 + C2*x + C3*x**2) / x) assert checkodesol(eqn, sol, order=3, solve_for_func=False)[0] assert sol == dsolve(eqn, f(x), prep=False, hint='nth_algebraic') @XFAIL def test_nth_algebraic_prep1(): eqn = Derivative(x*f(x), x, x, x) sol = Eq(f(x), (C1 + C2*x + C3*x**2) / x) assert checkodesol(eqn, sol, order=3, solve_for_func=False)[0] assert sol == dsolve(eqn, f(x), prep=True, hint='nth_algebraic') assert sol == dsolve(eqn, f(x)) # prep = True breaks this def test_nth_algebraic_noprep2(): eqn = Eq(Derivative(x*Derivative(f(x), x), x)/x, exp(x)) sol = Eq(f(x), C1 + C2*log(x) + exp(x) - Ei(x)) assert checkodesol(eqn, sol, order=2, solve_for_func=False)[0] assert sol == dsolve(eqn, f(x), prep=False, hint='nth_algebraic') @XFAIL def test_nth_algebraic_prep2(): eqn = Eq(Derivative(x*Derivative(f(x), x), x)/x, exp(x)) sol = Eq(f(x), C1 + C2*log(x) + exp(x) - Ei(x)) assert checkodesol(eqn, sol, order=2, solve_for_func=False)[0] assert sol == dsolve(eqn, f(x), prep=True, hint='nth_algebraic') assert sol == dsolve(eqn, f(x)) # This needs a combination of solutions from nth_algebraic and some other # method from dsolve @XFAIL def test_nth_algebraic_find_multiple2(): eqn = f(x)**2 + f(x)*f(x).diff(x) solns = [Eq(f(x), 0), Eq(f(x), C1*exp(-x))] assert all(c[0] for c in checkodesol(eqn, solns, order=1, solve_for_func=False)) assert set(solns) == dsolve(eqn, f(x)) # Needs to be a way to know how to combine derivatives in the expression @XFAIL def test_factoring_ode(): eqn = Derivative(x*f(x), x, x, x) + Derivative(f(x), x, x, x) soln = Eq(f(x), (C1*x**2/2 + C2*x + C3 - x)/(1 + x)) assert checkodesol(eqn, soln, order=2, solve_for_func=False)[0] assert soln == dsolve(eqn, f(x)) def test_issue_15913(): eq = -C1/x - 2*x*f(x) - f(x) + Derivative(f(x), x) sol = C2*exp(x**2 + x) + exp(x**2 + x)*Integral(C1*exp(-x**2 - x)/x, x) assert checkodesol(eq, sol) == (True, 0) sol = C1 + C2*exp(-x*y) eq = Derivative(y*f(x), x) + f(x).diff(x, 2) assert checkodesol(eq, sol, f(x)) == (True, 0) def test_issue_16146(): raises(ValueError, lambda: dsolve([f(x).diff(x), g(x).diff(x)], [f(x), g(x), h(x)])) raises(ValueError, lambda: dsolve([f(x).diff(x), g(x).diff(x)], [f(x)]))