testing whether a JuMP expression == 0

[chriscoey]

I am iterating over JuMP AffExprs and do not wish to add empty (0 == 0) constraints to a MIP model.

Can we have simple way to test whether an expression is just 0? i.e. for affine, the constant and all coefficients on variables are 0. It would be nice to be able to write if AffExpr == 0 blah blah.

[mlubin]

Whoever needs it is welcome to contribute a smarter definition of equality of AffExpr objects to handle duplicates and promotion.

[chriscoey]

@blegat is this what your PolyJuMP fix does at https://github.com/JuliaOpt/PolyJuMP.jl/pull/11/files#diff-ce657b38c7ecda6fbbcdcc558bf57b86?

[blegat]

Yes, this what is done in the PolyJuMP tests. Since JuMP is dropping v0.5, we can define this as Base.iszero in JuMP.

[chriscoey]

Great. Now that 0.5 support is dropped could you move this code to JuMP?

[mlubin]

Wrong package, still need a PR to drop 0.5 from JuMP.

[chriscoey]

Woops. Karma for using github mobile during a lunch date.

@mlubin can you drop 0.5 for jump too?

[mlubin]

iszero is implemented and tested: https://github.com/JuliaOpt/JuMP.jl/blob/e392cc873fecea188d6d8d52c891924900eabd13/test/operator.jl#L68
There's could be some debate about the definition and whether it should check for zero coefficients, but that could be a new issue.