Implement facets method for Polyhedron

[jipilab]

It is often practical to get directly the facets of a polyhedron object without having to compute or to know the dimension of the object.

This ticket implements the following shortcut:

sage: c = polytopes.hypercube(4)
sage: dim = c.dimension()
sage: c.faces(dim-1)
(A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices)

Now becomes:

sage: c = polytopes.hypercube(4)
sage: c.facets()
(A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices,
 A 3-dimensional face of a Polyhedron in ZZ^4 defined as the convex hull of 8 vertices)

[embray]

As the Sage-8.8 release milestone is pending, we should delete the sage-8.8 milestone for tickets that are not actively being worked on or that still require significant work to move forward. If you feel that this ticket should be included in the next Sage release at the soonest please set its milestone to the next release milestone (sage-8.9).

[selia]

New commits:

​8dc7dd5

implement facets

[chapoton]

Suggestion: add cross-references, in the new method:

        .. SEEALSO:: :meth:`faces`

and the same in the other direction

[jipilab]

Suggestion: in the files base.py, face.py, and library.py, perhaps it would be nice to change the tests involving faces(a_number_here) where the intented thing is really .facets.

This way, the function is advertized in the documentation of functions, and also well-tested.

There are sufficient tests with faces that are not facets not to have this a regression. Further, it still uses faces anyways. So no loss in strength of testing...

One comment about the bot result: The pyflake line is taken care of in #27993.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​76a87d7

added cross-references, changed faces examples to facets where appropriate

[jipilab]

LGTM, pyflakes errors are taken care of in #27993.

[vbraun]

Merge conflict

[jipilab]

Please remove the insertion of spaces in the banner.

The conflict is probably from the library somewhere...

[chapoton]

Looks good and the patchbot is green.

One detail needs to be fixed :

There is a seealso in facets referring to facets. It should refer to faces instead.

Once done, you can set to positive review on my behalf.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​e03f2ee

fixed seealso typo

[vbraun]

Merge conflict, please merge in the next beta

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​3362dc1	implement facets
​1ab0c3f	rebased facets on sage8.9.beta9
​e3621b8	fixed seealso typo

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​e3177be

banner fix

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​f72960d

banner fix again

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​743c4c7

added facets method to quickref

[chapoton]

ok, good to go