Add customizable subsolver direction to ALM

[mateuszbaran]

I mostly want to be able to set the memory to something less than 30.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (571b909) to head (8e5e56c).

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files           91        91           
  Lines        10027     10027           
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  Hits         10027     10027           

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[kellertuer]

I think instead of manually “passing down” more and more keywords (and introducing them with a sub_, I would prefer if you just use the sub_kwargs keyword. Would that be ok as well?

[mateuszbaran]

That would make sense but sub_kwargs already exists for ALM but it specifically excludes direction_update. Having direction_update in sub_kwargs would be a breaking change. I can also add direction_update to default sub_kwargs for Manopt 0.6 only.

[kellertuer]

That I do not understand why does it exclude the direction update?

Overall I am just unsure whether it is better to use sub_kwargs (keep the ALM keywords at a finite amount) or introduce more and more keywords to a solver that is a bit crowded on those already anyways.