Implementation of matplotlib backend for criterion_plot()

[r3kste]

Summary of Changes

1. Added backend parameter to criterion_plot() which accepts "plotly" or "matplotlib"
2. criterion_plot() now returns the figure object corresponding to the chosen backend.
3. Added backends.py which serves as a registry for all backends

To-Do

It is very much still a work in progress.

• Discuss on whether the dispatch mechanism can be improved.
• Add examples in documentation
• Add suitable tests

Plot

Plotly	Matplotlib

[codecov]

Codecov Report

❌ Patch coverage is 92.92035% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/optimagic/visualization/backends.py	90.47%	8 Missing ⚠️

Files with missing lines	Coverage Δ
src/optimagic/config.py	100.00% <100.00%> (ø)
src/optimagic/exceptions.py	88.57% <100.00%> (+0.33%)	⬆️
src/optimagic/visualization/history_plots.py	93.56% <100.00%> (+1.01%)	⬆️
src/optimagic/visualization/plotting_utilities.py	95.42% <100.00%> (+0.38%)	⬆️
src/optimagic/visualization/backends.py	90.47% <90.47%> (ø)

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[timmens]

Thanks a lot! I have a few comments, if you have any questions let me know here or via Zulip. I think it will be important to get this PR right such that we don't complicate our lives when handling the other visualization functions.

My main concern is that I'd like the usage of the plotting class to feel more natural. See one of my comments in the backends module.

On an abstract level, a plotting class supporting the criterion plot needs to be able to:

• Create a figure
• Add lines to that figure
• Set a template
• Set a legend position
• Set axis labels

Now I would expect that our plotting class somehow incorporates / supports these actions or an action that combines a subset of them (e.g., if we think that some of these actions comprise one block, like we currently do with the PlotConfig).

Additionally

1. As I am saying in one of the comments, we need to check whether we actually need the PlotConfig class.
2. I thought about your proposal to rename OptimizeResultOrPath to ResultOrPath, and I think I prefer that! Could you change that?

Thanks a lot!!

[timmens]

Thanks! This looks very very good now for the first proper version.

I only have a few comments. Most importantly, we need to make sure that matplotlib is treated as an optional dependency. Once this is handled we can move on to the other functions 🎉

[timmens]

Very nice, thanks a lot! Only a few clarifying comments, and then we are hopefully through with this.