lifting a subdivided matrix should preserve the subdivision, but doesn't.

[williamstein]

sage: a = random_matrix(GF(3),4)
sage: a.subdivide(2,2)
sage: a
[2 0|0 2]
[2 1|1 0]
[---+---]
[1 2|1 0]
[1 0|0 1]
sage: a.lift()
[2 0 0 2]
[2 1 1 0]
[1 2 1 0]
[1 0 0 1]

See also #5717.

CC: @jasongrout

Component: linear algebra

Author: John Palmieri

Reviewer: Jason Grout

Merged: 4.0.1.alpha0

Issue created by migration from https://trac.sagemath.org/ticket/5716

[sagetrac-mabshoff]

comment:2

Is this a high priority issue? I am not convinced and since there is no patch and no sign of anyone working on fixing this I am bumping this to 3.4.2. There are also various dupes, one of which go reopened, i.e. #5715, so let's figure this out.

Cheers,

Michael

[jhpalmieri]

comment:3

(I don't think this is actually a duplicate.)

[jhpalmieri]

comment:4

Here's a patch. This should change things so that subdivisions are preserved when calling mat.change_ring(), mat.lift(), mat.dense_matrix(), and mat.sparse_matrix().

[loefflerd]

comment:5

This applies fine to 4.0.rc1 and all doctests in sage/matrix pass (except the known numerical-noise failure which is nothing to do with this patch). But I'm not completely happy with it, because not all of the functions where the behaviour has changed have doctests to prove it, so I'm changing this to "needs work".

David

[jhpalmieri]

comment:6

Okay, here's a new patch. I think that this tests everything, although there is at least one function (sparse_matrix, maybe) which is tested in a doctest for another (by looking at a.dense_matrix().sparse_matrix() or something like that).

[jasongrout]

comment:7

Attachment: trac_5716.patch.gz

[jasongrout]

comment:8

It passes doctests (and everything is tested). Looks good to me. Positive review.

[mwhansen]

comment:9

Merged in 4.0.alpha0.

[mwhansen]

Merged: 4.0.1.alpha0

[mwhansen]

Reviewer: Jason Grout

[mwhansen]

Author: John Palmieri