Hello everybody !!! I was trying to write the following doctest, and noticed something scary :
We build a directed circulant graph on n vertices by linking the i th vertex to i+1, i+2, ... , i+k, thus ensuring our graph is k-connected. Then, by Edmond's theorem, we know this graph has `k` edge-disjoint spanning arborescences sage: n = 20 sage: k = 3 sage: g = DiGraph() sage: g.add_edges( (i,Mod(i+j,n)) for i in range(n) for j in range(1,k+1) ) sage: k == g.edge_connectivity() False This should be k, but it is not. Not *that* bad. But it gets worse : sage: g.strongly_connected_components() [[0], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]] Two different "0" ? Then I thought it was because of the Mod, and maybe some zeroes where regular ones, while other were zeroes of Z/20Z.... But then : sage: g Digraph on 21 vertices sage: len(g.vertices()) 20 sage: g.vertices() [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19] That's were I got really scared :-D Robert ? Could you please tell me "oh yeah, I know where it comes from, that's just a typo" ? :-D Thankssssssssssss !!! Nathann -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
