strongly_connected_components_digraph's had no edges

[nthiery]

Graphs produced with strongly_connected_components_digraph had no
edges in them due to a typo in the code:

    sage: g = DiGraph({0:[1,2,3],1:[2],2:[1,3]})
    sage: scc_digraph = g.strongly_connected_components_digraph()
    sage: scc_digraph.vertices()
    [{0}, {3}, {1, 2}]
    sage: scc_digraph.edges()
    []

After this patch, the result is more likely to be correct:

    [({0}, {3}, None), ({0}, {1, 2}, None), ({1, 2}, {3}, None)]

CC: @sagetrac-sage-combinat @rlmill

Component: graph theory

Keywords: strongly connected components

Author: Nicolas M. Thiéry

Reviewer: Nathann Cohen

Merged: sage-4.5.2.alpha0

Issue created by migration from https://trac.sagemath.org/ticket/9485

[nthiery]

comment:1

Attachment: trac_9485-strongly_connected_componnents_digraph-fix-nt.patch.gz

[nathanncohen]

comment:3

Oops... Some very, very bad typo ... Thank youuuuuuu ! :-)

Nathann

[nthiery]

Changed reviewer from Robert Miller to Nathann Cohen

[nthiery]

comment:4

Thanks for the instantaneous review!

And thanks as well for the original code. It was still quicker for me to fix it than to have to implement it myself :-)

[qed777]

Merged: sage-4.5.2.alpha0