Adds Graph.treewidth()
quick fix
quick fix for smooth triangles too
don't use __str__ or __repr__ for tachyon string representations
fix doctests
more doctest fixes
use verbose option to check that plots render successfully
trac #16709: IncidenceStructure.packing
correct docstring for str
trac #16741: Bug in IncidenceStructure.relabel when the ground set consists of pairs
Trac #16226: Tachyon plot produces invalid file

`Tachyon.plot` does not produce valid syntax for `tachyon_rt`.  The
basic problem is that triangles are not printed correctly: they show as
tuples instead.  This means that the [http://www.sagemath.org/doc/refere
nce/plot3d/sage/plot/plot3d/tachyon.html#sage.plot.plot3d.tachyon.Tachyo
n.plot examples in the reference manual] are broken.

Here is a minimal example:

{{{
sage: m = lambda u,v: u^2 - v^3
sage: Q = Tachyon(camera_center=(5,0,4))
sage: Q.texture('t')
sage: Q.light((-20,-20,40), 0.2, (1,1,1))
sage: Q.plot(m,(0,1),(0,1),'t',max_depth=1,initial_depth=1)
}}}

The string tachyon tries to render is this:
{{{
sage: print(Q.str())

        begin_scene
...
        light center  -20.0 -20.0 40.0
              rad 0.2
              color  1.0 1.0 1.0

(1/2, 0, 1/4) (1/2, 1/2, 1/8) (1/4, 1/4, 3/64) t(1/2, 0, 1/4) (1/2, 1/2,
1/8) (3/4, 1/4, 35/64) t
...
        end_scene

}}}

Instead of 3-tuples, we should see something like this:
{{{
...
        TRI V0  0.5 0.0 0.25   V1  0.5 0.5 0.125    V2  0.25 0.25
0.046875
            t

        TRI V0  0.5 0.0 0.25   V1  0.5 0.5 0.125    V2  0.75 0.25
0.546875
            t
...
}}}

URL: http://trac.sagemath.org/16226
Reported by: niles
Ticket author(s): Niles Johnson
Reviewer(s): Frédéric Chapoton
Trac #16709: IncidenceStructure.packing

A Good Old ILP for a NP-Hard problem. Reminds me of the early days of
Graphs in Sage `:-P`

Nathann

URL: http://trac.sagemath.org/16709
Reported by: ncohen
Ticket author(s): Nathann Cohen
Reviewer(s): Dima Pasechnik
Trac #16741: Bug in IncidenceStructure.automorphism_group when the ground set consists of pairs

Before

{{{
sage: designs.IncidenceStructure([[(1,2),(3,4)]]).automorphism_group()
...
ValueError: Invalid permutation vector: [(3, 4), (1, 2)]
}}}

After

{{{
sage: designs.IncidenceStructure([[(1,2),(3,4)]]).automorphism_group()
Permutation Group with generators [((1,2),(3,4))]
}}}

URL: http://trac.sagemath.org/16741
Reported by: ncohen
Ticket author(s): Nathann Cohen
Reviewer(s): Dima Pasechnik
trac #15181: Merged with 6.3.beta8
trac #15181: Reviewer's remarks
Trac #15181: Treewidth (lazy implementation)

This code is a veeeery lazy implementation of a very lazy algorithm to
compute the treewidth of a graph. It can be greatly improved in at least
two places.

If it is to be improved later, this implementation will probably remain
useful anyway, as we try to always keep many of them alive, just to
check whether they all return sound results. Hence it's not so bad if it
is a bit wasteful `:-P`

And well. It's great to have this, too `:-P`

Nathann

URL: http://trac.sagemath.org/15181
Reported by: ncohen
Ticket author(s): Nathann Cohen
Reviewer(s): David Coudert