cleanup non-decreasing parking functions

[fchapoton]

in particular get rid of CombinatorialClass there (#12913)

CC: @tscrim

Component: combinatorics

Author: Frédéric Chapoton

Branch/Commit: 12bca39

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/26384

[fchapoton]

New commits:

07177d0

get rid of CombinatorialClass for non-decreasing parking functions

[fchapoton]

Branch: u/chapoton/26384

[fchapoton]

Commit: 07177d0

[fchapoton]

comment:2

Maybe I should have kept CombinatorialObject ?

[tscrim]

comment:3

Replying to @fchapoton:

Maybe I should have kept CombinatorialObject ?

That one is a maybe. The biggest issue is they are no longer hashable:

sage: hash(NonDecreasingParkingFunction([]))
11648069979105038

which is an error on your branch. It is possible that someone is using the other list-like features of CombinatorialObject not already reimplemented (mainly the __add__ being concatenation), but I find that highly unlikely.

[tscrim]

comment:4

IIRC, Nicolas has told me we should use ClonableArray instead of CombinatorialObject/Element. Although I do not like some of the features of the former (mainly, the hash and equality depends on the parent, which can cause lots of subtle problems with objects that live in multiple incompatible (wrt to coercion) parents). Here, however, this would be a reasonable thing to inherit from.

[fchapoton]

comment:5

Travis, do you think this could enter sage in the current state ? I would prefer not to spend more time on that..

[tscrim]

comment:6

I think it is probably better in the long run to not use CombinatorialObject. However, it does need a __hash__. Other than that, it is good to go.

[sagetrac-git]

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

12bca39

trac 26384 adding hash

[sagetrac-git]

Changed commit from 07177d0 to 12bca39

[fchapoton]

comment:8

ok, I have added the hash. Thanks a lot for your help.

[tscrim]

comment:9

No problem. Thanks for fixing that.

[tscrim]

Reviewer: Travis Scrimshaw

[vbraun]

Changed branch from u/chapoton/26384 to 12bca39