Dear Robert If you look at the help message for is_transitive() then you see that the definition is this: A digraph is transitive if for any pair of vertices u,v in G linked by a uv-path the edge uv belongs to G.
Cheers Nico 2014-02-07 19:35 GMT+01:00 Robert <[email protected]>: > A student in my discrete structures course found what he thinks is a bug > in Sage's treatment of directed graphs. Consider the relation given by the > Python dictionary: > > {0: [1], 1: [0], 2: [3], 3: [2]} > > So 0 is related to 1 and vice versa, and 2 is related to 3 and vice versa. > This is NOT a transitive relation, because if it were, then 0 would have to > be related to itself. (I.e. there would be a loop on the directed graph at > 0.) > > However, when you enter the following code: > > *r = {0: [1], 1: [0], 2: [3], 3: [2]} * > *g = DiGraph(r)* > *g.is_transitive()* > > ...you get "True". Is this because is_transitive has a bug; because Sage > doesn't like its directed graphs to have loops; because the is_transitive > method is using a different definition of "transitive" than we are*, or > what? > > Thanks in advance! > Robert > > * For example it could be using a definition of transitive that says "For > all DISTINCT a,b,c in A, if (a,b) and (b,c) then (a,c)." I don't know. > > -- > You received this message because you are subscribed to the Google Groups > "sage-edu" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sage-edu. > For more options, visit https://groups.google.com/groups/opt_out. > -- You received this message because you are subscribed to the Google Groups "sage-edu" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sage-edu. For more options, visit https://groups.google.com/groups/opt_out.
