Add lp_matrix_data

[odow]

Closes #3572

TODO:

• documentation
• bike shed the name
• check lp_sensitivity tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3015564) 98.38% compared to head (d269bf2) 98.38%.
Report is 2 commits behind head on master.

Additional details and impacted files

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##           master    #3573   +/-   ##
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  Coverage   98.38%   98.38%           
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  Files          37       38    +1     
  Lines        5629     5648   +19     
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+ Hits         5538     5557   +19     
  Misses         91       91           

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[jd-foster]

StandardFormData ?

[odow]

Other options:

• lp_standard_form(model)
• lp_matrix_data(model)
• standard_matrix_data(model)
• standard_matrix_form(model)
• standard_form_matrix(model)
• standard_form_matrix_data(model)

I think I like lp_matrix_data. LPMatrixData is a bit ugly, but okay for the name of a struct.

[jd-foster]

I think the name works well.

[odow]

@blegat, I think I can anticipate your comment: why not Utilities.MatrixOfConstraints.

I think we potentially could in future, but this is a simple first pass. I'm more interested in your thoughts on the user-facing data structure. There's an argument for providing a matrix and a vector of sets, or A <sense> b, but I think we should target what 99% of people want, which is the matrix and vectors from an LP.