Don't know if this is a bug, but sage numerically disagrees with a paper about strong product of graphs.
The paper is: Strong products of Kneser graphs, Sandi Klavˇar and Uroˇ Milutinovi ́ at: http://www.fmf.uni-lj.si/~klavzar/preprints/Kneser.pdf Let "*" denote the strong product. p.4 theorem 1: If G has at least one edge then \chi (G * K_n) >= \chi(G) + 2n - 2 for G= C_4 and n = 3 the lower bound is 6. In sage 5.4: sage: C4=graphs.CycleGraph(4);K=graphs.CompleteGraph(3) sage: G=C4.strong_product(K) sage: G.chromatic_number() 5 sage: F=K.strong_product(C4) sage: F.chromatic_number() 5 So sage's \chi is lower than the lower bound. There is exact bound involving Kneser graph. I implemented |strong_product| and don't get the same products as sage (C_4 bound passed, the Kneser one didn't pass with my code). What is the drama? (Didn't audit sage's strong_product). -- You received this message because you are subscribed to the Google Groups "sage-support" group. To post to this group, send email to sage-support@googlegroups.com. To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com. Visit this group at http://groups.google.com/group/sage-support?hl=en.
