category of lazy family wrong if infinite combinatorial class used as index

[cnassau]

sage: from sage.sets.set_from_iterator import EnumeratedSetFromIterator
sage: C=CombinatorialFreeModule(ZZ,EnumeratedSetFromIterator(Integers)) ; C
Free module generated by {0, 1, -1, 2, -2, ...} over Integer Ring
sage: U = tensor((C,)) ; U
Free module generated by {0, 1, -1, 2, -2, ...} over Integer Ring
sage: C.basis().category()
Category of enumerated sets
sage: U.basis().category()
Category of finite enumerated sets

But clearly the basis of U is not finite.

Depends on #19195

CC: @tscrim

Component: categories

Author: Christian Nassau

Branch/Commit: u/cnassau/18849 @ 09f97fa

Reviewer: Vincent Delecroix

Issue created by migration from https://trac.sagemath.org/ticket/18849

[cnassau]

Author: Christian Nassau

[cnassau]

comment:1

Source of this problem is that the tensor product uses a sage.combinat.combinat.MapCombinatorialClass for the cartesian product, and the LazyFamily constructor assumed all CombinatorialClass objects to be finite. An extra check for is_finite has been added in this case. The check is caught since is_finite might not be implemented.

Note that it's important not to treat the negative answer of is_finite as affirmation that the class is actually infinite; whether the set is finite or not might just not be known, or to expansive to check.

---

New commits:

b553884

fix category detection for LazyFamily objects

[cnassau]

Branch: u/cnassau/18849

[cnassau]

Commit: b553884

[sagetrac-git]

Changed commit from b553884 to 82849a0

[sagetrac-git]

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

82849a0

fix category detection for LazyFamily objects

[sagetrac-git]

Changed commit from 82849a0 to 09f97fa

[sagetrac-git]

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

09f97fa

fix category detection for LazyFamily objects

[cnassau]

comment:4

A first patchbot run gave this error:

**********************************************************************
File "src/sage/interfaces/expect.py", line 825, in sage.interfaces.expect.Expect._eval_line
Failed example:
    singular.interrupt(timeout=3)  # sometimes very slow (up to 60s on sage.math, 2012)
Expected:
    False
Got:
    True
**********************************************************************
1 item had failures:
   1 of  15 in sage.interfaces.expect.Expect._eval_line
    [89 tests, 1 failure, 9.38 s]
----------------------------------------------------------------------
sage -t --long --warn-long 69.5 src/sage/interfaces/expect.py  # 1 doctest failed
----------------------------------------------------------------------

I think this is completely unrelated and random; I have cleaned up an empty line in the commit, so a new run should be triggered soon.

[videlec]

comment:5

Hello,

1. Why a special care for CombinatorialClass is even needed at all? The following would be much simpler

category = EnumeratedSets()
if set in Sets().Finite() or isinstance(set, (list,tuple)):
    category = category.Finite()
elif set in Sets().Infinite():
    category = category.Infinite()

2. Your documentation lines are too long.

Vincent