Complete MatrixObj

[fingolfin]

This issue is supposed to be the "main issue" for completing the MatrixObj code in the GAP library, which is meant to replace (or complement) our current matrix code (which represents matrices as lists of lists) with proper "matrix objects", which internally can be represented in different ways (as lists of lists in row-major or column-major form; as a list of rows*columns entries; as various kinds of sparse matrices; as compressed matrices; etc.).

I'll try to list some things that needs to be done for MatrixObj to be "complete". But we shouldn't necessarily add everything here, instead we can file separate issues, and also organize these into a GitHub "project", see https://github.com/gap-system/gap/projects/1

(I really have no idea whether everything should be in a separate issue, or in one big list, or... whatever, just do what seems natural. The important thing in the end is to actual code stuff anyway, not how we log the open tasks :-)

Edit (@ssiccha):
I have collected all TODO lists into this hackmd. It contains a "Good first issues" section at the top of the TODO list. All comments in this thread containing TODOs are now hidden. A backup is in a gist and in a fork of mine.

[fingolfin]

We have several people who are interested to help with MatrixObj (e.g. @AnnaKDS @danielrademacher @wucas @ssiccha @FriedrichRober) but this is difficult as we lack a clear plan and tasks to assign. This issue was meant to be a master plan, but it doesn't really prioritize things or give specific steps. Moreover, we have too many TODO/task lists; besides what is in here, there is also ...

• the list of issues in the MatrixObj "project"
• this TODO file https://github.com/gap-system/gap/blob/master/dev/TODO_matobj.txt
• a source code comment in lib/matobj2.gd
• some older slides by Thomas also contain some TODOs
• my old slides don't contain TODOs but give some points as to why MatrixObj is needed, we should have this somewhere easily accessible, too

Ideally I'd like there to be a single place for this, which we then try to keep up-to-date. I think @ThomasBreuer was looking a bit into it, not sure what came of that.

[fingolfin]

@ThomasBreuer just reminded me that we also created https://hackmd.io/WAShW7z9Rp2rJRq1AVnWAQ

[ssiccha]

I'm putting all of our TODO lists into the hackmd linked by @fingolfin. Then I'm gonna try and sort out duplicates.

Edit: I'm finished sorting out duplicates. I haven't checked whether any of the TODOs are outdated though. I'm hiding all comments containing TODO lists as outdated now.