Fix pdf export of graphs

[defeo]

The following code raises an error

sage: p = graphs.CompleteGraph(2).plot()
sage: p.save('tmp.pdf')
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
...
AssertionError: 

The error seems to be caused by edges, indeed

sage: p = graphs.CompleteGraph(1).plot()
sage: p.save('tmp.pdf')

works fine.

Depends on #14993

CC: @nthiery

Component: graphics

Keywords: graph plot

Issue created by migration from https://trac.sagemath.org/ticket/15116

[sagetrac-edward-scheinerman]

comment:2

Interesting. Indeed a two vertex, zero edge graph also works fine:

sage: g = Graph(2)
sage: pic = g.plot()
sage: pic.save('two-verts.pdf')

[mezzarobba]

comment:3

This looks very much like matplotlib/matplotlib#2418. The patch given there (included in matplotlib-1.3.1) fixes the issue.

[nathanncohen]

comment:4

Gosh ! They have quivers there too ? O_O

Good news, though. Well, it means that we need to upgrade matplotlib now :-)

Nathann

[mezzarobba]

Dependencies: 14993

[fchapoton]

Changed dependencies from 14993 to #14993

[fchapoton]

comment:9

works in 6.3.beta1

[nathanncohen]

comment:10

Frederic : when you set a ticket to "wontfix", please change its status to positive_review.

Nathann