Sorry, I meant n=8. sage: print [ec(n) for n in range(9)] [1, 1, 1, 2, 3, 4, 6, 5, 8]
On Mon, Oct 29, 2012 at 11:41 AM, Tom Boothby <tomas.boot...@gmail.com> wrote: > Wanna run that on connected graphs? I get the correct sequence out to n=9 for > > def ec(n) > c = 0 > for g in graphs(n): > if g.is_connected() and g.line_graph().is_vertex_transitive(): > c+= 1 > return c > > > > On Mon, Oct 29, 2012 at 11:37 AM, Jernej Azarija <azi.std...@gmail.com> wrote: >> Hello! >> >> Yes but this appears to be even more bogus. Consider this: >> >> == >> def ec(n): >> c = 0 >> for el in graphs.nauty_geng(str(n)): >> if (el.line_graph()).is_vertex_transitive(): >> c+=1 >> return c >> == >> >> sage: ec(7) >> 27 >> sage: ec(8) >> 39 >> >> But there are 26 and 40 edge-transitive graphs on 7 and 8 nodes >> respectively. It appears as if something is wrong with the computation of >> the automorphism group of a graph. >> >> Can someone comment on that? >> >> >> >> >> >> >> >> >> On Monday, 29 October 2012 19:29:56 UTC+1, Tom wrote: >>> >>> I use G.line_graph().is_vertex_transitive() >>> >>> On Mon, Oct 29, 2012 at 7:12 AM, Jernej Azarija <azi.s...@gmail.com> >>> wrote: >>> > Hello! >>> > >>> > I am slowly implementing a patch that will provide some features for >>> > symmetry testing of graphs. >>> > >>> > However I am already puzzled by the following attempt at testing for >>> > edge-transitive graphs. Here is a straightforward textbook >>> > implementation >>> > (the presented code omits the exceptional treatment of the singleton >>> > graph) >>> > >>> > === >>> > def is_edge_transitive(self): >>> > >>> > A,T = self.automorphism_group(translation=True) >>> > for (x,y,_) in self.edges(): >>> > acts = set([]) >>> > for g in A: >>> > a,b = g(T[x]),g(T[y]) >>> > acts.add((a,b) if a < b else (b,a)) >>> > if len(acts) == self.size(): >>> > return True >>> > return False >>> > === >>> > >>> > Testing the code (Petersen, Gray and path graph) it appears as if the >>> > results are correct. But considering the following function computing >>> > the >>> > number connected edge transitive graphs of given order >>> > >>> > === >>> > def ecc(n): >>> > c = 0 >>> > for el in graphs.nauty_geng(str(n)+ " -c "): >>> > if el.is_edge_transitive(): >>> > c+=1 >>> > return c >>> > === >>> > >>> > we observe that >>> > >>> > sage: [ecc(i) for i in xrange(2,9)] >>> > [1, 2, 3, 4, 6, 5, 8] >>> > >>> > which does not coincide with the data provided at oeis: >>> > http://oeis.org/A095424/list . The difference gets even bigger if we >>> > count >>> > all edge-transitive graphs instead of just connected. >>> > >>> > Anyone happens to see the flaw in the is_edge_transitive method? >>> > >>> > Best, >>> > >>> > Jernej >>> > >>> > -- >>> > You received this message because you are subscribed to the Google >>> > Groups >>> > "sage-devel" group. >>> > To post to this group, send email to sage-...@googlegroups.com. >>> > To unsubscribe from this group, send email to >>> > sage-devel+...@googlegroups.com. >>> > Visit this group at http://groups.google.com/group/sage-devel?hl=en. >>> > >>> > >> >> -- >> You received this message because you are subscribed to the Google Groups >> "sage-devel" group. >> To post to this group, send email to sage-devel@googlegroups.com. >> To unsubscribe from this group, send email to >> sage-devel+unsubscr...@googlegroups.com. >> Visit this group at http://groups.google.com/group/sage-devel?hl=en. >> >> -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To post to this group, send email to sage-devel@googlegroups.com. To unsubscribe from this group, send email to sage-devel+unsubscr...@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel?hl=en.
