# References : # http://www.euclideanspace.com/maths/algebra/realNormedAlgebra/quaternions/ # https://en.wikipedia.org/wiki/Quaternion from __future__ import print_function from sympy.core.expr import Expr from sympy import Rational from sympy import re, im, conjugate from sympy import sqrt, sin, cos, acos, asin, exp, ln from sympy import trigsimp from sympy import diff, integrate from sympy import Matrix, Add, Mul from sympy import symbols, sympify from sympy.printing.latex import latex from sympy.printing import StrPrinter from sympy.core.numbers import Integer from sympy.core.compatibility import SYMPY_INTS class Quaternion(Expr): """Provides basic quaternion operations. Quaternion objects can be instantiated as Quaternion(a, b, c, d) as in (a + b*i + c*j + d*k). Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> q = Quaternion(1, 2, 3, 4) >>> q 1 + 2*i + 3*j + 4*k Quaternions over complex fields can be defined as : ======== >>> from sympy.algebras.quaternion import Quaternion >>> from sympy import symbols, I >>> x = symbols('x') >>> q1 = Quaternion(x, x**3, x, x**2, real_field = False) >>> q2 = Quaternion(3 + 4*I, 2 + 5*I, 0, 7 + 8*I, real_field = False) >>> q1 x + x**3*i + x*j + x**2*k >>> q2 (3 + 4*I) + (2 + 5*I)*i + 0*j + (7 + 8*I)*k """ _op_priority = 11.0 is_commutative = False def __new__(cls, a=0, b=0, c=0, d=0, real_field=True): a = sympify(a) b = sympify(b) c = sympify(c) d = sympify(d) if any(i.is_commutative is False for i in [a, b, c, d]): raise ValueError("arguments have to be commutative") else: obj = Expr.__new__(cls, a, b, c, d) obj._a = a obj._b = b obj._c = c obj._d = d obj._real_field = real_field return obj @property def a(self): return self._a @property def b(self): return self._b @property def c(self): return self._c @property def d(self): return self._d @property def real_field(self): return self._real_field @classmethod def from_axis_angle(cls, vector, angle): """Returns a rotation quaternion given the axis and the angle of rotation. Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> from sympy import pi, sqrt >>> q = Quaternion.from_axis_angle((sqrt(3)/3, sqrt(3)/3, sqrt(3)/3), 2*pi/3) >>> q 1/2 + 1/2*i + 1/2*j + 1/2*k """ (x, y, z) = vector norm = sqrt(x**2 + y**2 + z**2) (x, y, z) = (x / norm, y / norm, z / norm) s = sin(angle * Rational(1, 2)) a = cos(angle * Rational(1, 2)) b = x * s c = y * s d = z * s return cls(a, b, c, d).normalize() @classmethod def from_rotation_matrix(cls, M): """Returns the equivalent quaternion of a matrix. The quaternion will be normalized only if the matrix is special orthogonal (orthogonal and det(M) = 1). Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> from sympy import Matrix, symbols, cos, sin, trigsimp >>> x = symbols('x') >>> M = Matrix([[cos(x), -sin(x), 0], [sin(x), cos(x), 0], [0, 0, 1]]) >>> q = trigsimp(Quaternion.from_rotation_matrix(M)) >>> q sqrt(2)*sqrt(cos(x) + 1)/2 + 0*i + 0*j + sqrt(-2*cos(x) + 2)/2*k """ absQ = M.det()**Rational(1, 3) a = sqrt(absQ + M[0, 0] + M[1, 1] + M[2, 2]) / 2 b = sqrt(absQ + M[0, 0] - M[1, 1] - M[2, 2]) / 2 c = sqrt(absQ - M[0, 0] + M[1, 1] - M[2, 2]) / 2 d = sqrt(absQ - M[0, 0] - M[1, 1] + M[2, 2]) / 2 try: b = Quaternion.__copysign(b, M[2, 1] - M[1, 2]) c = Quaternion.__copysign(c, M[0, 2] - M[2, 0]) d = Quaternion.__copysign(d, M[1, 0] - M[0, 1]) except Exception: pass return Quaternion(a, b, c, d) @staticmethod def __copysign(x, y): # Takes the sign from the second term and sets the sign of the first # without altering the magnitude. if y == 0: return 0 return x if x*y > 0 else -x def __add__(self, other): return self.add(other) def __radd__(self, other): return self.add(other) def __sub__(self, other): return self.add(other*-1) def __mul__(self, other): return self._generic_mul(self, other) def __rmul__(self, other): return self._generic_mul(other, self) def __pow__(self, p): return self.pow(p) def __neg__(self): return Quaternion(-self._a, -self._b, -self._c, -self.d) def _eval_Integral(self, *args): return self.integrate(*args) def _eval_diff(self, *symbols, **kwargs): return self.diff(*symbols) def add(self, other): """Adds quaternions. Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> from sympy import symbols >>> q1 = Quaternion(1, 2, 3, 4) >>> q2 = Quaternion(5, 6, 7, 8) >>> q1.add(q2) 6 + 8*i + 10*j + 12*k >>> q1 + 5 6 + 2*i + 3*j + 4*k >>> x = symbols('x', real = True) >>> q1.add(x) (x + 1) + 2*i + 3*j + 4*k Quaternions over complex fields : ======== >>> from sympy.algebras.quaternion import Quaternion >>> from sympy import I >>> q3 = Quaternion(3 + 4*I, 2 + 5*I, 0, 7 + 8*I, real_field = False) >>> q3.add(2 + 3*I) (5 + 7*I) + (2 + 5*I)*i + 0*j + (7 + 8*I)*k """ q1 = self q2 = sympify(other) # If q2 is a number or a sympy expression instead of a quaternion if not isinstance(q2, Quaternion): if q1.real_field: if q2.is_complex: return Quaternion(re(q2) + q1.a, im(q2) + q1.b, q1.c, q1.d) else: # q2 is something strange, do not evaluate: return Add(q1, q2) else: return Quaternion(q1.a + q2, q1.b, q1.c, q1.d) return Quaternion(q1.a + q2.a, q1.b + q2.b, q1.c + q2.c, q1.d + q2.d) def mul(self, other): """Multiplies quaternions. Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> from sympy import symbols >>> q1 = Quaternion(1, 2, 3, 4) >>> q2 = Quaternion(5, 6, 7, 8) >>> q1.mul(q2) (-60) + 12*i + 30*j + 24*k >>> q1.mul(2) 2 + 4*i + 6*j + 8*k >>> x = symbols('x', real = True) >>> q1.mul(x) x + 2*x*i + 3*x*j + 4*x*k Quaternions over complex fields : ======== >>> from sympy.algebras.quaternion import Quaternion >>> from sympy import I >>> q3 = Quaternion(3 + 4*I, 2 + 5*I, 0, 7 + 8*I, real_field = False) >>> q3.mul(2 + 3*I) (2 + 3*I)*(3 + 4*I) + (2 + 3*I)*(2 + 5*I)*i + 0*j + (2 + 3*I)*(7 + 8*I)*k """ return self._generic_mul(self, other) @staticmethod def _generic_mul(q1, q2): q1 = sympify(q1) q2 = sympify(q2) # None is a Quaternion: if not isinstance(q1, Quaternion) and not isinstance(q2, Quaternion): return q1 * q2 # If q1 is a number or a sympy expression instead of a quaternion if not isinstance(q1, Quaternion): if q2.real_field: if q1.is_complex: return q2 * Quaternion(re(q1), im(q1), 0, 0) else: return Mul(q1, q2) else: return Quaternion(q1 * q2.a, q1 * q2.b, q1 * q2.c, q1 * q2.d) # If q2 is a number or a sympy expression instead of a quaternion if not isinstance(q2, Quaternion): if q1.real_field: if q2.is_complex: return q1 * Quaternion(re(q2), im(q2), 0, 0) else: return Mul(q1, q2) else: return Quaternion(q2 * q1.a, q2 * q1.b, q2 * q1.c, q2 * q1.d) return Quaternion(-q1.b*q2.b - q1.c*q2.c - q1.d*q2.d + q1.a*q2.a, q1.b*q2.a + q1.c*q2.d - q1.d*q2.c + q1.a*q2.b, -q1.b*q2.d + q1.c*q2.a + q1.d*q2.b + q1.a*q2.c, q1.b*q2.c - q1.c*q2.b + q1.d*q2.a + q1.a * q2.d) def _eval_conjugate(self): """Returns the conjugate of the quaternion.""" q = self return Quaternion(q.a, -q.b, -q.c, -q.d) def norm(self): """Returns the norm of the quaternion.""" q = self # trigsimp is used to simplify sin(x)^2 + cos(x)^2 (these terms # arise when from_axis_angle is used). return sqrt(trigsimp(q.a**2 + q.b**2 + q.c**2 + q.d**2)) def normalize(self): """Returns the normalized form of the quaternion.""" q = self return q * (1/q.norm()) def inverse(self): """Returns the inverse of the quaternion.""" q = self if not q.norm(): raise ValueError("Cannot compute inverse for a quaternion with zero norm") return conjugate(q) * (1/q.norm()**2) def pow(self, p): """Finds the pth power of the quaternion. Returns the inverse if p = -1. Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> q = Quaternion(1, 2, 3, 4) >>> q.pow(4) 668 + (-224)*i + (-336)*j + (-448)*k """ q = self if p == -1: return q.inverse() res = 1 if p < 0: q, p = q.inverse(), -p if not (isinstance(p, (Integer, SYMPY_INTS))): return NotImplemented while p > 0: if p & 1: res = q * res p = p >> 1 q = q * q return res def exp(self): """Returns the exponential of q (e^q). Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> q = Quaternion(1, 2, 3, 4) >>> q.exp() E*cos(sqrt(29)) + 2*sqrt(29)*E*sin(sqrt(29))/29*i + 3*sqrt(29)*E*sin(sqrt(29))/29*j + 4*sqrt(29)*E*sin(sqrt(29))/29*k """ # exp(q) = e^a(cos||v|| + v/||v||*sin||v||) q = self vector_norm = sqrt(q.b**2 + q.c**2 + q.d**2) a = exp(q.a) * cos(vector_norm) b = exp(q.a) * sin(vector_norm) * q.b / vector_norm c = exp(q.a) * sin(vector_norm) * q.c / vector_norm d = exp(q.a) * sin(vector_norm) * q.d / vector_norm return Quaternion(a, b, c, d) def _ln(self): """Returns the natural logarithm of the quaternion (_ln(q)). Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> q = Quaternion(1, 2, 3, 4) >>> q._ln() log(sqrt(30)) + 2*sqrt(29)*acos(sqrt(30)/30)/29*i + 3*sqrt(29)*acos(sqrt(30)/30)/29*j + 4*sqrt(29)*acos(sqrt(30)/30)/29*k """ # _ln(q) = _ln||q|| + v/||v||*arccos(a/||q||) q = self vector_norm = sqrt(q.b**2 + q.c**2 + q.d**2) q_norm = q.norm() a = ln(q_norm) b = q.b * acos(q.a / q_norm) / vector_norm c = q.c * acos(q.a / q_norm) / vector_norm d = q.d * acos(q.a / q_norm) / vector_norm return Quaternion(a, b, c, d) def pow_cos_sin(self, p): """Computes the pth power in the cos-sin form. Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> q = Quaternion(1, 2, 3, 4) >>> q.pow_cos_sin(4) 900*cos(4*acos(sqrt(30)/30)) + 1800*sqrt(29)*sin(4*acos(sqrt(30)/30))/29*i + 2700*sqrt(29)*sin(4*acos(sqrt(30)/30))/29*j + 3600*sqrt(29)*sin(4*acos(sqrt(30)/30))/29*k """ # q = ||q||*(cos(a) + u*sin(a)) # q^p = ||q||^p * (cos(p*a) + u*sin(p*a)) q = self (v, angle) = q.to_axis_angle() q2 = Quaternion.from_axis_angle(v, p * angle) return q2 * (q.norm()**p) def diff(self, *args): return Quaternion(diff(self.a, *args), diff(self.b, *args), diff(self.c, *args), diff(self.d, *args)) def integrate(self, *args): # TODO: is this expression correct? return Quaternion(integrate(self.a, *args), integrate(self.b, *args), integrate(self.c, *args), integrate(self.d, *args)) @staticmethod def rotate_point(pin, r): """Returns the coordinates of the point pin(a 3 tuple) after rotation. Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> from sympy import symbols, trigsimp, cos, sin >>> x = symbols('x') >>> q = Quaternion(cos(x/2), 0, 0, sin(x/2)) >>> trigsimp(Quaternion.rotate_point((1, 1, 1), q)) (sqrt(2)*cos(x + pi/4), sqrt(2)*sin(x + pi/4), 1) >>> (axis, angle) = q.to_axis_angle() >>> trigsimp(Quaternion.rotate_point((1, 1, 1), (axis, angle))) (sqrt(2)*cos(x + pi/4), sqrt(2)*sin(x + pi/4), 1) """ if isinstance(r, tuple): # if r is of the form (vector, angle) q = Quaternion.from_axis_angle(r[0], r[1]) else: # if r is a quaternion q = r.normalize() pout = q * Quaternion(0, pin[0], pin[1], pin[2]) * conjugate(q) return (pout.b, pout.c, pout.d) def to_axis_angle(self): """Returns the axis and angle of rotation of a quaternion Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> q = Quaternion(1, 1, 1, 1) >>> (axis, angle) = q.to_axis_angle() >>> axis (sqrt(3)/3, sqrt(3)/3, sqrt(3)/3) >>> angle 2*pi/3 """ q = self try: # Skips it if it doesn't know whether q.a is negative if q.a < 0: # avoid error with acos # axis and angle of rotation of q and q*-1 will be the same q = q * -1 except BaseException: pass q = q.normalize() angle = trigsimp(2 * acos(q.a)) # Since quaternion is normalised, q.a is less than 1. s = sqrt(1 - q.a*q.a) x = trigsimp(q.b / s) y = trigsimp(q.c / s) z = trigsimp(q.d / s) v = (x, y, z) t = (v, angle) return t def to_rotation_matrix(self, v=None): """Returns the equivalent rotation transformation matrix of the quaternion which represents rotation about the origin if v is not passed. Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> from sympy import symbols, trigsimp, cos, sin >>> x = symbols('x') >>> q = Quaternion(cos(x/2), 0, 0, sin(x/2)) >>> trigsimp(q.to_rotation_matrix()) Matrix([ [cos(x), -sin(x), 0], [sin(x), cos(x), 0], [ 0, 0, 1]]) Generates a 4x4 transformation matrix (used for rotation about a point other than the origin) if the point(v) is passed as an argument. Example ======== >>> from sympy.algebras.quaternion import Quaternion >>> from sympy import symbols, trigsimp, cos, sin >>> x = symbols('x') >>> q = Quaternion(cos(x/2), 0, 0, sin(x/2)) >>> trigsimp(q.to_rotation_matrix((1, 1, 1))) Matrix([ [cos(x), -sin(x), 0, sin(x) - cos(x) + 1], [sin(x), cos(x), 0, -sin(x) - cos(x) + 1], [ 0, 0, 1, 0], [ 0, 0, 0, 1]]) """ q = self s = q.norm()**-2 m00 = 1 - 2*s*(q.c**2 + q.d**2) m01 = 2*s*(q.b*q.c - q.d*q.a) m02 = 2*s*(q.b*q.d + q.c*q.a) m10 = 2*s*(q.b*q.c + q.d*q.a) m11 = 1 - 2*s*(q.b**2 + q.d**2) m12 = 2*s*(q.c*q.d + q.b*q.a) m20 = 2*s*(q.b*q.d - q.c*q.a) m21 = 2*s*(q.c*q.d + q.b*q.a) m22 = 1 - 2*s*(q.b**2 + q.c**2) if not v: return Matrix([[m00, m01, m02], [m10, m11, m12], [m20, m21, m22]]) else: (x, y, z) = v m03 = x - x*m00 - y*m01 - z*m02 m13 = y - x*m10 - y*m11 - z*m12 m23 = z - x*m20 - y*m21 - z*m22 m30 = m31 = m32 = 0 m33 = 1 return Matrix([[m00, m01, m02, m03], [m10, m11, m12, m13], [m20, m21, m22, m23], [m30, m31, m32, m33]])