Variable Encoding

[pedromxavier]

We are currently dealing with variables according to a ::Symbol parameter used to chose how encoding and expansion takes place.

The current VirtualVariable UI takes:

• Variable bounds [a, b]
• Encoding technique (Unary/Binary x Binary/Discrete/Real)
• Is Semidiscrete/Semicontinuous? (Not in use, but already implemented at this level)
• A variable factory function for initialization
• A source variable from the original model (if it is not a slack)
• number of bits
• variable name (we need it?)

I'm considering refactoring our UI using something like an EncodingType in a similiar fashion as we did with quadratization methods.

The expansion is currently done via Base.iterate(::VirtualVariable) and Base.collect(::VirtualVarible). Both methods yield ::Set{VI}, ::Float64 pairs, which is very PBF-friendly. Indeed, the syntax PBF{VI, Float64}(collect(::VirtualVariable{VI, Float64})) works very well.

A more suitable output UI should also be under investigation since one-hot-encoding (our next milestone) requires the addition of a uniqueness constraint among the generated variables.