Polyhedra coercion of base rings fails for number fields

[kliem]

Currently coercion of polyhedra with number fields does not work. The following results in a type error:

sage: z = QQ['z'].0                                          
sage: K = NumberField(z^2 - 2,'s')
sage: K.gen()*polytopes.simplex(backend='field')

But the backend can surely handle it, as the following does work:

sage: z = QQ['z'].0                                          
sage: K = NumberField(z^2 - 2,'s')
sage: K.gen()*polytopes.simplex(backend='field', base_ring=K)
A 3-dimensional polyhedron in (Number Field in s with defining polynomial z^2 - 2)^4 defined as the convex hull of 4 vertices

The underlying error:

sage: z = QQ['z'].0                                          
sage: K = NumberField(z^2 - 2,'s')
sage: parent = polytopes.simplex().parent()
sage: parent._coerce_base_ring(K)
Rational Field

But it should be K.

The problem is that _coerce_base_ring of Polyhedra_base just takes the base ring of K, which are the rationals.

We fix this, by not taking the base ring, if the object is already a ring.

CC: @jplab @LaisRast

Component: geometry

Author: Jonathan Kliem

Branch/Commit: a0068cc

Reviewer: Léo Brunswic

Issue created by migration from https://trac.sagemath.org/ticket/28770

[kliem]

Description changed:

--- 
+++ 
@@ -15,6 +15,18 @@
 A 3-dimensional polyhedron in (Number Field in s with defining polynomial z^2 - 2)^4 defined as the convex hull of 4 vertices
 ```
 
-The problem is that `_coerce_base_ring` of `Polyhedra` just takes the base ring of `K`, which are the rationals.
+The underlying error:
+
+```
+sage: z = QQ['z'].0                                          
+sage: K = NumberField(z^2 - 2,'s')
+sage: parent = polytopes.simplex().parent()
+sage: parent._coerce_base_ring(K)
+Rational Field
+```
+
+But it should be `K`.
+
+The problem is that `_coerce_base_ring` of `Polyhedra_base` just takes the base ring of `K`, which are the rationals.
 
 We fix this, by not taking the base ring, if the object is already a ring.

[kliem]

Commit: a272cfd

[kliem]

New commits:

a272cfd

fix coercion of polyhedra with number fields

[kliem]

Branch: public/28770

[sagetrac-git]

Changed commit from a272cfd to a0068cc

[sagetrac-git]

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

a0068cc

added a doctest for the original bug

[fchapoton]

comment:4

reviewer full name is missing

[kliem]

Reviewer: Léo Brunswic