Fix bug in chessboard graphs generator

[dcoudert]

We should normally have:

• The BishopGraph([d1,d2],radius=r) is isomorphic to the graph obtained merging the edges of the KnightGraphs([d1,d2],one=i,two=i) for 1<= i <= r.
• The QueenGraph([d1,d2],radius=r) is isomorphic to the graph obtained merging the edges of a RookGraph([d1,d2,radius=r) and a BishopGraph([d1,d2],radius=r)

With current implementation, the result was sometimes incorrect. This patch solves this issue and adds necessary doctests.

CC: @sagetrac-sluther @nathanncohen

Component: graph theory

Author: David Coudert

Reviewer: Nathann Cohen

Merged: sage-5.6.beta0

Issue created by migration from https://trac.sagemath.org/ticket/13813

[dcoudert]

comment:1

Attachment: trac_13813.patch.gz

[nathanncohen]

comment:2

I was about to say that you should replace if not B.is_isomorphic(H) by if B != H, but...

sage: %timeit B == H
5 loops, best of 3: 199 ms per loop
sage: %timeit B.is_isomorphic(H)
25 loops, best of 3: 16.3 ms per loop

Honestly ...>_<

Nathann

[dcoudert]

comment:3

Thanks.

[jdemeyer]

Reviewer: Nathann Cohen

[jdemeyer]

Merged: sage-5.6.beta0