QuadraticRepnVisitor: Improve nonlinear expression expansion

[jsiirola]

Fixes #2275 .

Summary/Motivation:

This resolves some issues in the QuadraticRepnVisitor nonlinear term expansion logic. In particular, it needed specialized handlers for LINEAR * GENERAL and GENERAL * GENERAL so that nonlinear terms are correctly expanded when expand_nonlinear_products is True.

Changes proposed in this PR:

• Register handlers for LINEAR * GENERAL, GENERAL * LINEAR, and GENERAL * GENERAL
• Add a trap to prevent the unnecessary inclusion of "0*" terms in expanded products
• Add tests for the examples from Extract linear/quadratic/nonlinear terms from nonlinear expressions #2275

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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.22% 🎉

Comparison is base (c471729) 87.85% compared to head (0992622) 88.08%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2997      +/-   ##
==========================================
+ Coverage   87.85%   88.08%   +0.22%     
==========================================
  Files         769      769              
  Lines       89497    89496       -1     
==========================================
+ Hits        78632    78835     +203     
+ Misses      10865    10661     -204     

Flag	Coverage Δ
linux	85.19% <100.00%> (+1.45%)	⬆️
osx	74.99% <100.00%> (+<0.01%)	⬆️
other	85.36% <100.00%> (+1.45%)	⬆️
win	82.43% <100.00%> (+0.04%)	⬆️

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Files Changed	Coverage Δ
pyomo/repn/quadratic.py	93.08% <100.00%> (+2.07%)	⬆️

... and 6 files with indirect coverage changes

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[mrmundt]

Just so I understand - _GENERAL implies nonlinear, correct?

[jsiirola]

Yes.

[jsiirola]

...I used "GENERAL" as a shorthand for "General nonlinear", because just using "NONLINEAR" would have been confusing with QUADRATIC.

[michaelbynum]

Looks good.

Unrelated - what is the default for expand_nonlinear_products?

[jsiirola]

@michaelbynum: The default is currently False (because it is not needed for the LP writer), but I was thinking about it this morning, and I was going to propose (either here or at the Dev call) that we change the default to True, and then the LP writer could set it explicitly to False.

[michaelbynum]

@michaelbynum: The default is currently False (because it is not needed for the LP writer), but I was thinking about it this morning, and I was going to propose (either here or at the Dev call) that we change the default to True, and then the LP writer could set it explicitly to False.

I like that proposal. The expansion is very powerful, and I don't think we should "hide" that functionality (I realize it is not really hidden, but, hopefully, you get my point).