Bug in incidence_matrix of CombinatorialPolyhedron

[LaisRast]

The incidence_matrix method of a 0-dimensional CombinatorialPolyhedron returns an error:

sage: P = Polyhedron([[0]]); P
A 0-dimensional polyhedron in ZZ^1 defined as the convex hull of 1 vertex
sage: C = P.combinatorial_polyhedron()
sage: C.incidence_matrix()
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-7-dab311ba238f> in <module>()
----> 1 C.incidence_matrix()
...
ValueError: ``output_dimension`` must be the dimension of proper faces

We fix this and make the 0-dimensional case consistent with Polyhedron_base.

Also we make incidence_matrix a chached_method.

CC: @jplab @kliem

Component: geometry

Keywords: polytope, combinatorialpolyhedron, incidence_matrix

Author: Jonathan Kliem

Branch/Commit: 34f3254

Reviewer: Laith Rastanawi

Issue created by migration from https://trac.sagemath.org/ticket/29455

[kliem]

New commits:

4aa8b28

fix incidence matrix for small combinatorial polyhedra

[kliem]

Author: Jonathan Kliem

[kliem]

Description changed:

--- 
+++ 
@@ -12,3 +12,7 @@
 ...
 ValueError: ``output_dimension`` must be the dimension of proper faces
 ```
+
+We fix this and make the `0`-dimensional case consistent with `Polyhedron_base`.
+
+Also we make `incidence_matrix` a `chached_method`.

[kliem]

Commit: 4aa8b28

[kliem]

Branch: public/29455

[LaisRast]

comment:2

This fixes the problem.

[LaisRast]

Reviewer: Laith Rastanawi

[kliem]

comment:3

Thanks