Allowing constant objective function

[kibaekkim]

No description provided.

[kibaekkim]

It is strange that Real <: AbstractJuMPScalar returns false. This could have been addressed in JuMP. But, this commit would resolve that.

[blegat]

Real is not an AbstractJuMPScalar as it does not corresponds to any MOI scalar function.
We should rather do as in jump-dev/JuMP.jl#2247

[kibaekkim]

Real is not an AbstractJuMPScalar as it does not corresponds to any MOI scalar function.
We should rather do as in jump-dev/JuMP.jl#2247

@blegat Can you elaborate a bit more about your suggestion? Is this comment on b25afc9?
My fix was base on https://github.com/jump-dev/JuMP.jl/blob/release-0.21/src/objective.jl#L107-L114

[blegat]

Add a method

function JuMP.set_objective_function(m::StructuredModel, f::Real)
    JuMP.set_objective_function(m, convert(AffExpr, f))
end

It should work once jump-dev/JuMP.jl#2247 is merged. We should do a patch release of JuMP including this PR soon so that won't block this PR for long

[kibaekkim]

@blegat can you check if the changes are compatible to the PR?

[blegat]

Add in Project.toml that we require at least JuMP v0.21.3

[kibaekkim]

@blegat any other concerns or suggestions?