ó ,ľ[c@s_dZddlZddlmZddgZedƒedƒdd „ƒƒZd „ZdS( sTFunctions related to the Mycielski Operation and the Mycielskian family of graphs. i˙˙˙˙N(tnot_implemented_fort mycielskiantmycielski_graphtdirectedt multigraphicsÜ|jƒ‰tj|ƒ}xşt|ƒD]Ź}|jƒ‰|jtˆdˆƒƒt|jƒƒ}|j‡fd†|Dƒƒ|j‡fd†|Dƒƒ|jdˆƒ|j‡fd†tˆƒDƒƒq(W|S(s_Returns the Mycielskian of a simple, undirected graph G The Mycielskian of graph preserves a graph's triangle free property while increasing the chromatic number by 1. The Mycielski Operation on a graph, :math:`G=(V, E)`, constructs a new graph with :math:`2|V| + 1` nodes and :math:`3|E| + |V|` edges. The construction is as follows: Let :math:`V = {0, ..., n-1}`. Construct another vertex set :math:`U = {n, ..., 2n}` and a vertex, `w`. Construct a new graph, `M`, with vertices :math:`U \bigcup V \bigcup w`. For edges, :math:`(u, v) \in E` add edges :math:`(u, v), (u, v + n)`, and :math:`(u + n, v)` to M. Finally, for all vertices :math:`u \in U`, add edge :math:`(u, w)` to M. The Mycielski Operation can be done multiple times by repeating the above process iteratively. More information can be found at https://en.wikipedia.org/wiki/Mycielskian Parameters ---------- G : graph A simple, undirected NetworkX graph iterations : int The number of iterations of the Mycielski operation to perform on G. Defaults to 1. Must be a non-negative integer. Returns ------- M : graph The Mycielskian of G after the specified number of iterations. Notes ------ Graph, node, and edge data are not necessarily propagated to the new graph. ic3s%|]\}}||ˆfVqdS(N((t.0tutv(tn(s<lib/python2.7/site-packages/networkx/generators/mycielski.pys Fsc3s%|]\}}|ˆ|fVqdS(N((RRR(R(s<lib/python2.7/site-packages/networkx/generators/mycielski.pys Gsc3s#|]}|ˆdˆfVqdS(iN((RR(R(s<lib/python2.7/site-packages/networkx/generators/mycielski.pys Is( tnumber_of_nodestnxtconvert_node_labels_to_integerstrangetadd_nodes_fromtlisttedgestadd_edges_fromtadd_node(tGt iterationstMtit old_edges((Rs<lib/python2.7/site-packages/networkx/generators/mycielski.pyRs,  'cCsU|dkrtjdƒ‚n|dkr7tjdƒSttjdƒ|dƒSdS(s‡Generator for the n_th Mycielski Graph. The Mycielski family of graphs is an infinite set of graphs. :math:`M_1` is the singleton graph, :math:`M_2` is two vertices with an edge, and, for :math:`i > 2`, :math:`M_i` is the Mycielskian of :math:`M_{i-1}`. More information can be found at http://mathworld.wolfram.com/MycielskiGraph.html Parameters ---------- n : int The desired Mycielski Graph. Returns ------- M : graph The n_th Mycielski Graph Notes ----- The first graph in the Mycielski sequence is the singleton graph. The Mycielskian of this graph is not the :math:`P_2` graph, but rather the :math:`P_2` graph with an extra, isolated vertex. The second Mycielski graph is the :math:`P_2` graph, so the first two are hard coded. The remaining graphs are generated using the Mycielski operation. ismust satisfy n >= 0iN(R t NetworkXErrort empty_graphRt path_graph(R((s<lib/python2.7/site-packages/networkx/generators/mycielski.pyRNs    (t__doc__tnetworkxR tnetworkx.utilsRt__all__RR(((s<lib/python2.7/site-packages/networkx/generators/mycielski.pyt s    9