Tidy src/variable.jl

[odow]

@ericphanson thoughts on :Bin vs BinVar? I assume your long-term plan was to deprecate the symbols? They're pretty brittle and the docs don't mention the Symbol approach.

[ericphanson]

Yeah, that was the plan. After using it intermittently though I don’t really like the *Var suffixes; they are hard to remember and look a bit weird. I’m definitely open to alternative approaches!

[odow]

What about MOI.ZeroOne and MOI.Integer, or the Base types Int and Bool?

[ericphanson]

Either of those seems better! The MOI ones might help folks connect the dots with MOI more, while the Base ones might look less scary. Both could lead to the issue of folks trying other objects that aren’t supported, but we could give good errors.

I see JuMP supports Int, Bin, and binary=true, so that could also make sense here.

[ericphanson]

Btw now that JuMP supports generic number types, it seems ok to lower to jump rather than MOI- maybe that could allow better interop, like mixing Convex and JuMP variables in a model. I bring this up here since I suspect Bin is from JuMP, not MOI.

[odow]

I think we want to keep lowering to MOI instead of JuMP. We have some ideas for DCP in JuMP. One is to lower JuMP's nonlinear expressions to Convex (requires jump-dev/MathOptInterface.jl#2402).

The other is to add DCP support to JuMP directly. Working through this code base is giving me some ideas. But this is a long-term thing. Nothing in the short-term.

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (0e42f97) 97.76% compared to head (56e8132) 97.94%.

Files	Patch %	Lines
src/variable.jl	93.75%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #583      +/-   ##
==========================================
+ Coverage   97.76%   97.94%   +0.18%     
==========================================
  Files          91       91              
  Lines        5060     5069       +9     
==========================================
+ Hits         4947     4965      +18     
+ Misses        113      104       -9     

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[blegat]

Btw now that JuMP supports generic number types, it seems ok to lower to jump rather than MOI- maybe that could allow better interop, like mixing Convex and JuMP variables in a model

You can already mix any constraints supported by JuMP with DCP constraints when using Convex.Optimizer, what would using Convex at the JuMP level achieve ? Mixing the Convex expressions and the JuMP expressions is tricky, it was the approach of ParameterJuMP but we're now going the other direction with ParametricOptInterface. I feel staying at the MOI level where you only need to care about the MOI API and not arbitrary interaction with the user is easier :)

[odow]

see JuMP supports Int, Bin, and binary=true, so that could also make sense here.

[odow]

see JuMP supports Int, Bin, and binary=true, so that could also make sense here.

Ah, but it is the symbol :Int in the macro and not the Base.Int type. And same with :Bin, because Bin does not exist as a type (or object) in Base or JuMP...

Variable(2, 3; binary = true) is okay. So is Variable(Bool) and Variable(Int). You can't mix Bool and Int, and you can do Semidefinite(2, Int) or Semidefinite(2, Bool) if you reeeeally wanted? (I don't know if we really have a MISDP solver.)

Perhaps this is a separate PR through.