Multiple loops handling in c_graph

[sagetrac-brunellus]

Sage handles multiple loops on one vertex inconsistently.

sage:g=Graph({0:[0,0]}, loops=True, multiedges=True, implementation="c_graph")
sage:g.edges()
[(0, 0, None), (0, 0, None)]
sage:g.delete_edge(0,0)
sage:g.edges()
[]

Compare with

sage:g=Graph({0:[0,0]}, loops=True, multiedges=True, implementation="networkx")
sage:g.edges()
[(0, 0, None), (0, 0, None)]
sage:g.delete_edge(0,0)
sage:g.edges()
[(0, 0, None)]

and

sage:g=Graph({0:[1,1]}, loops=True, multiedges=True, implementation="c_graph")
sage:g.edges()
[(0, 1, None), (0, 1, None)]
sage:g.delete_edge(0,1)
sage:g.edges()
[(0, 1, None)]

Apply:

• attachment: trac_12135_loop_removal.patch
• attachment: trac_12135_review.patch

Component: graph theory

Keywords: Cernay2012

Author: Lukáš Lánský

Reviewer: Nathann Cohen

Merged: sage-5.0.beta4

Issue created by migration from https://trac.sagemath.org/ticket/12135

[sagetrac-brunellus]

comment:1

A loop is stored as a single arc, but del_edge removes both ends:

self._cg.del_arc_label(u_int, v_int, l_int)
self._cg.del_arc_label(v_int, u_int, l_int)

So...

sage: g=Graph({0:[0]*11}); len(g.edges())
11
sage: g.delete_edge(0,0); len(g.edges())
9
sage: g.delete_edge(0,0); len(g.edges())
7
sage: g.delete_edge(0,0); len(g.edges())
5

[sagetrac-brunellus]

comment:2

OK, this was rather easy.

[nathanncohen]

comment:3

Attachment: trac_12135_loop_removal.patch.gz

Helloooooooo !!!

Here is a one-line patch to add the "::" at the end of the line before the tests. If if it ok with you, the patch can be set to "positive_review". :-)

Nathann

(and I changed the subject because I am at Cernay with the combinat team, and that is how they want to remember which patches we worked on... Sorry about that ^^;)

[sagetrac-brunellus]

comment:5

Attachment: trac_12135_review.patch.gz

Sorry, I keep forgetting about that. :-/ Thanks for the review. :-)

[sagetrac-brunellus]

Reviewer: Nathann Cohen

[sagetrac-brunellus]

Author: Lukáš Lánský

[nathanncohen]

comment:7

Looks like it shouldn't be in the topic but in the keywords... ^^;

Thank you for the patches and the names :-)

Nathann

[nathanncohen]

Changed keywords from none to Cernay2012

[jdemeyer]

Merged: sage-5.0.beta4