Various improvements to AdaptVQE

[mrossinek]

Summary

This PR adds a few minor improvements to the AdaptVQE implementation.
Mostly more logging to make it easier to follow the progress of the algorithm.

Details and comments

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[coveralls]

Pull Request Test Coverage Report for Build 3649047896

• 16 of 16 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 84.593%

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Totals
Change from base Build 3649046642:	0.003%
Covered Lines:	63411
Relevant Lines:	74960

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💛 - Coveralls

[woodsp-ibm]

As this adds history to the result object an end user sees I think this should have a reno, and that also perhaps mentions the additional logging since that's also something an end user can enable/view. As far as the history - this is the eigenvalues at each iteration right - maybe the docstring could be clearer in that regard - does it include the final value too in the history?

[woodsp-ibm]

Could we include testing the eigenvalue_history, maybe in one (or more) of the existing tests, to ensure its there in the result as expected.

[mrossinek]

Could we include testing the eigenvalue_history, maybe in one (or more) of the existing tests, to ensure its there in the result as expected.

Will do that next week 👍

I was actually also thinking just now, that we could also store the gradient history as this might be useful in post-processing, too

[Cryoris]

@Mergifyio requeue

[mergify]

requeue

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