Gurobi solution pool tweak

[viens-code]

Fixes #3725

Summary/Motivation:

Adds the ability to do best effort solution pool collection

Changes proposed in this PR:

• Adds ability to change flag in solution pool to 1, best effort instead of defaulting to 2 in gurobi solution pool tools
• Running in best effort mode gives a warning that unexpected behavior may occur, per gurobi documentation: https://docs.gurobi.com/projects/optimizer/en/current/features/solutionpool.html

Legal Acknowledgement

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1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[viens-code]

Is this a my code issue or an issue with win/3.9 and 3.13?
It didn't get to the pyomo tests and my only changes were in contrib.alternative_solutions

[mrmundt]

@viens-code - neither were related to your code. The 3.9 one was a spurious failure; the 3.13 one is now just happening everywhere (yay broken infrastructure). I'm looking into it.

[jsiirola]

One requested change for a test, but more fundamentally, why is this needed? Can't users get exactly the same behavior with

gurobi_generate_solutions(..., solver_options={'PoolSearchMode': 2})

[jsiirola]

This is a weak test: not only will any assertion that fails pass, but not raising any error at all will also pass. The recommended / standard way to test an error is to check both the error type and the message:

with self.assertRaisesRegex(AssertionError, "pool_search_mode must be 1 or 2"):
    gurobi_generate_solutions(m, pool_search_mode=0)

[viens-code]

Changed over to the suggested format

[viens-code]

First, will make the tweaks to the testing logic to update to your suggestion, thank you for that.

To the larger point, there are a couple of things going on with the alternative_solutions package.
One of which is trying to make the alternative solutions methods easier to use for people who couldn't/wouldn't write the custom functionality for themselves.

Yes an advanced user could change from enforced enumerate (mode 2) to best effort (mode 1) with the manual flag if they knew about it.
The functionality add here was about adding best-effort solution discovery as a clear option in contrib.alternative_solutions.

It also parallels how things like num_solutions are handled as parameters outside solver_options.
We could do solver_options={'PoolSolutions': num_solutions} instead there too.

[blnicho]

@viens-code as you're working on additional changes, please make sure to merge main into your branch. This will resolve the win/3.13 failure which is coming from a testing infrastructure issue.

[viens-code]

Changes to that test structure done

[viens-code]

@mrmundt @blnicho
So we seem to have different failures on win/3.10, are these also just Pyomo CI issues like before?

[blnicho]

@viens-code seems like it was a temporary CI issue. Re-running the win/3.10 job seems to have resolved it.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.32%. Comparing base (7816915) to head (1138a36).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3726      +/-   ##
==========================================
+ Coverage   89.27%   89.32%   +0.04%     
==========================================
  Files         896      896              
  Lines      103687   103695       +8     
==========================================
+ Hits        92567    92622      +55     
+ Misses      11120    11073      -47     

Flag	Coverage Δ
builders	29.09% <0.00%> (?)
default	85.93% <100.00%> (?)
expensive	35.86% <0.00%> (?)
linux	86.96% <100.00%> (-2.09%)	⬇️
linux_other	86.96% <100.00%> (+<0.01%)	⬆️
osx	83.10% <100.00%> (+<0.01%)	⬆️
win	85.22% <100.00%> (+<0.01%)	⬆️
win_other	85.22% <100.00%> (+<0.01%)	⬆️

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[whart222]

I agree with Matthew's argument that the pool_search_mode provides a convenient API simplification that will make it easier for end-users.

[viens-code]

Tweaks made to handling the solver options as requested in code review.

[jsiirola]

This is getting close... In addition to @blnicho's bugfix, some additional quick changes would be good:

[viens-code]

Ok, all of the changes should be made now.
Also added a missing test beyond what was requested for num_solutions = 0 case to test that assertation warning

Edit: And of course I forget to apply black. Now fixed

[viens-code]

Spelling Change. The word 'assertation' breaks the spellchecker

[jsiirola]

There are a couple lines that are too long (the strings constants should be split), but overall, this is fine.