Bug in the associahedron object

[jplab]

The following lines currently occur:

sage: A = polytopes.associahedron(['A',3])
sage: face = A.faces(2)[3]
sage: face
<6,8,9,10>
sage: face.as_polyhedron()
/home/jplabbe/sage/local/lib/python2.7/site-packages/sage/repl/rich_output/display_manager.py:590: RichReprWarning: Exception in _rich_repr_ while displaying object: 'Associahedra_with_category.element_class' object has no attribute '_cartan_type'
  RichReprWarning,
<repr(<sage.combinat.root_system.associahedron.Associahedra_with_category.element_class at 0x7f48d0d7ad70>) failed: AttributeError: 'Associahedra_with_category.element_class' object has no attribute '_cartan_type'>

The construction as_polyhedron initializes the new (face-)polyhedron via P.__class__(parent, Vrep, None). In the case of the associahedron, this does not give a valid object, as the associahedron requires a cartan type as well.

Same (or similar problem) with:

• minkowski_sum,
• minkowski_difference,
• translation,
• dilation,
• convex_hull,
• intersection (actually even worse as coercion fails),
• polar.

We fix the initialization of the associahedron to now require the cartan type on __init__ (before it was assumed to be set after initialization).

Further we have __new__ return the correct parent class such that e.g. the face of an Associahedron_class_ppl is constructed as Polyhedron_ppl.

We fix _coerce_map_from_ to take into account that no general polyhedron can be coerced to an associahedron.

We manually set the correct pushout of polyhedra over ZZ and associahedra (over QQ) to be polyhedra over QQ.

Depends on #27798

CC: @fchapoton @stumpc5 @tscrim @mo271 @jplab @LaisRast

Component: geometry

Keywords: associahedron

Author: Jonathan Kliem

Branch/Commit: d9083b7

Reviewer: Jean-Philippe Labbé, Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/25183

[kliem]

comment:2

I think I took care of it in #27798.

[kliem]

Description changed:

--- 
+++ 
@@ -10,3 +10,9 @@
   RichReprWarning,
 <repr(<sage.combinat.root_system.associahedron.Associahedra_with_category.element_class at 0x7f48d0d7ad70>) failed: AttributeError: 'Associahedra_with_category.element_class' object has no attribute '_cartan_type'>
 ```
+
+The construction `as_polyhedron` initializes the new (face-)polyhedron as via `P.__class__(parent, Vrep, None)`. In the case of the associahedron, this does not give a valid object, as the associahedron requires a cartan type as well.
+
+We fix the initialization of the associahedron to now require the cartan type on `__init__` (before it was assumed to be set after initialization).
+
+Further we have `__new__` return the correct parent class such that e.g. the face of an `Associahedron_class_ppl` is constructed as `Polyhedron_ppl`.

[kliem]

Author: Jonathan Kliem

[kliem]

comment:3

This branch should fix the bug.

Feel free to change it, alter it, abonden it, etc.

Maybe there is a better way to obtain the correct parent, i.e. improve the following lines:

156             for typ1 in ancestors_of_associahedron:
157                 if typ1 in mro:
158                     return typ1(parent, Vrep, Hrep, **kwds)

---

New commits:

2643078	added `backend` to associahedron and flow polytope
a9b4826	typo
8716985	corrected docstring
b873156	associahedron actually uses the claimed backend now
1f4bb25	comments by tscrim
2c812c5	should have fixed bug in #25183
65b11c9	removed redundant line

[kliem]

Commit: 65b11c9

[kliem]

Branch: public/25183

[kliem]

Dependencies: 27798

[kliem]

Changed dependencies from 27798 to #27798