Add Base.vec(M::MatElem)

[lgoettgens]

The code originates in https://github.com/oscar-system/Oscar.jl/blob/597398c594796cd2abbd8749977cb3f2a20eefb2/experimental/GModule/GModule.jl#L1451, but I want to use it in other parts of Oscar, that should not depend on experimental. So the cleanest solution is to add it here.
Note that this code currently operates in column-wise fashion (should this be changed?)

To reduce any conflicts in Oscar, it would be easiest to include this in the next breaking release, and then remove the corresponding things in https://github.com/oscar-system/Oscar.jl/blob/597398c594796cd2abbd8749977cb3f2a20eefb2/experimental/GModule/GModule.jl#L1451.

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (b4d4de5) 86.98% compared to head (7c4c5b8) 86.96%.

❗ Current head 7c4c5b8 differs from pull request most recent head de7a624. Consider uploading reports for the commit de7a624 to get more accurate results

Files	Patch %	Lines
src/Matrix.jl	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1614      +/-   ##
==========================================
- Coverage   86.98%   86.96%   -0.03%     
==========================================
  Files         114      114              
  Lines       29686    29695       +9     
==========================================
  Hits        25823    25823              
- Misses       3863     3872       +9     

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[thofma]

Not clear to me if we want this.

[lgoettgens]

Not clear to me if we want this.

If we don't want this, this shouldn't be in Oscar as well (pinging @fieker).

But I think we should definitely have a cheap way to convert a matrix to a vector (or 1xn / nx1 matrix)

[fieker]

On Mon, Feb 19, 2024 at 04:32:07AM -0800, Lars Göttgens wrote: > Not clear to me if we want this. If we don't want this, this shouldn't be in Oscar as well (pinging @fieker).

It is/ was neccessary, if we want this, it also needs to be done in Nemo for the Nemo types.

…

But I think we should definitely have a cheap way to convert a matrix to a vector -- Reply to this email directly or view it on GitHub: #1614 (comment) You are receiving this because you were mentioned. Message ID: ***@***.***>

[thofma]

1. We should not have it in this form for the same reason we don't have linear indexing: It is ambiguous.
2. Is violates A == matrix(A, nrows(A), ncols(A), vec(A))
3. If it exists, it must be a view/reshape.

[thofma]

I am happy to rename it to _vec in Oscar and postpone this discussion.

[fingolfin]

This seems to be controversial and I also don't see a good way to implement this efficiently without a lot of effort. So is this really worth pursuing?

If @lgoettgens still has need, perhaps we should discuss it during triage?

[lgoettgens]

Iirc we resolved the problem in a different way