make fun optional when fun_and_jac is provided

[gauravmanmode]

Closes #518

Proposed Solution

if fun_and_jac is not None, and fun is not provided, set fun from fun_and_jac.
Also adjusted the docs.
I have added a test also.

[review-notebook-app]

Check out this pull request on 

See visual diffs & provide feedback on Jupyter Notebooks.

---

Powered by ReviewNB

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files with missing lines	Coverage Δ
...imagic/optimization/create_optimization_problem.py	88.18% <100.00%> (+0.20%)	⬆️

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[janosg]

Hi @gauravmanmode, thanks for the PR.

We want to support this, but there is one edge case that makes it slightly harder: As you can see here, jac or fun_and_jac can be a list of callables if users want to switch seamlessly between scalar and least_squares optimizers. In that case we would have to select the correct entry from the list before we can call split_fun_and_jac. But at the point where you are handling this case we don't even know yet which entry we would need.

My plan was to wait until version 0.6 where we can remove a lot of deprecated code that currently limits the order in which we can process user inputs.

But we can keep your PR as a step in the right direction if you raise an error for the (very rare) case that fun_and_jac is a list.

[gauravmanmode]

you are right. i dont know how to handle this. since you said it is a rare case, i have raised a error and added a test.

[janosg]

Thanks @gauravmanmode, this is looking really good now. I only had a few small suggestions that should be very quick to address.

[gauravmanmode]

@janosg thanks for the suggestions. i hope this resolves them.

[janosg]

Thanks a lot; This is good to merge now!