The license of nauty is not gpl compatible, so we can't distribute it with
Sage. There is an optional package that you can try if you want.
On Friday, February 28, 2014 10:18:44 PM UTC+1, Aleksandr Kodess wrote:
>
> As far as I know both sage and magma utilize Brendan McKay's program nauty
> in order to check whether two given graphs (directed or undirected) are
> isomorphic. As is demonstrated by the following example, sage and magma
> greatly differ in the efficiency in which this program is utilized.
>
> # sage code
> q = 19
> n1 = 7
> n2 = 13
> F = FiniteField(q, 'xi')
> V = [(x,y) for x in F for y in F]
> G1 = DiGraph([V, lambda x,y: x[1] + y[1] == x[0]*(y[0]**n1)])
> G2 = DiGraph([V, lambda x,y: x[1] + y[1] == x[0]*(y[0]**n2)])
> G1.is_isomorphic(G2)
>
> // magma code for the same operation
> q := 19;
> n1 := 7;
> n2 := 13;
> F := FiniteField(q);
> V := {[x,y] : x,y in F};
> G1 := Digraph< V|{ [x,y] : x,y in V | x[2] + y[2] eq
> ((x[1])^1)*((y[1])^n1)}>;
> G2 := Digraph< V|{ [x,y] : x,y in V | x[2] + y[2] eq
> ((x[1])^1)*((y[1])^n2)}>;
> IsIsomorphic(G1,G2);
>
>
> It takes sage forever to test whether these two directed graphs of order
> 19^2 are isomorphic (they are in fact not), while it takes magma only a
> second. The same problem occurs for other values of q, n1 and n2. The
> version of sage I'm running is 5.12, and the version of magma I'm running
> is 2.19.10.
>
> Is this a known issue? Is this going to be fixed any time soon?
>
>
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