Retrieving the basis solution

[matheusdiogenesandrade]

Hello.

I am trying to obtain the status of variables in the basis solution. The issue covered this topic with a previous version of this package. But, it seems that the proposed solution doesn't work for the current package version, so, I took the time to try to write my own function for this, but I am struggling in the step for retrieving the corresponding variables mapping.

For instance, let's consider the following use case.

model = direct_model(CPLEX.Optimizer())
@variable(model, y[["a", "b"]])
# constraints

optimize!(model)

c_basis, r_basis = get_basis(model)

# c_basis["a"] =  CPX_AT_LOWER	        0	variable y["a"] at lower bound
#                 CPX_BASIC	        1	variable y["a"] is basic
#                 CPX_AT_UPPER	        2	variable y["a"] at upper bound
#                 CPX_FREE_SUPER	3	variable y["a"] free and nonbasic

A "partial snippet" is given below.

function get_basis(model::Model)
    cval = Vector{Cint}(num_variables(model))
    rval = Vector{Cint}(num_constraints(model))

    ret = CPXgetbase(model.moi_backend.env, model.moi_backend.lp, cval, rval)
    ret != 0 && throw(PROPEREXCEPTION(model.moi_backend.env, ret))
    # ...
end

I would like to know how I could complete the above function.

Thanks and regards.

[odow]

See https://jump.dev/JuMP.jl/dev/tutorials/linear/basis/

There is no need to use the low-level C API.

If you have more questions, please post on the Discourse forum: https://discourse.julialang.org/c/domain/opt/13

[matheusdiogenesandrade]

See https://jump.dev/JuMP.jl/dev/tutorials/linear/basis/

There is no need to use the low-level C API.

If you have more questions, please post on the Discourse forum: https://discourse.julialang.org/c/domain/opt/13

Thank you very much.