Diagnosing an infeasible model can be tricky. Sometimes solvers provide useful information like conflict reports and the constraints involved in the infeasibility - for these to be useful, we have to be able to relate the reported constraint with a constraint in our model. This currently works well for reugular constraints which can be named. However, variable bounds and integrality constraints, to the best of my knowledge are not named and when these are the cause of/involved in an infeasibility, it is difficult to dagnose. If we could name these constraints, it would be great. Is it / could it be possible?
Variables have names. A reference like “integrality constraint on variable XYZ” should be sufficient, right?
Do you have an example in which the integrality or bound constraint not being named is a problem?
I don’t really understand where it would show up as an issue.
julia> using JuMP, Gurobi
julia> model = Model(Gurobi.Optimizer)
A JuMP Model
Feasibility problem with:
Variables: 0
Model mode: AUTOMATIC
CachingOptimizer state: EMPTY_OPTIMIZER
Solver name: Gurobi
julia> @variable(model, x >= 1)
x
julia> @constraint(model, c, x <= 0)
c : x ≤ 0.0
julia> optimize!(model)
Gurobi Optimizer version 10.0.0 build v10.0.0rc2 (mac64[x86])
CPU model: Intel(R) Core(TM) i5-8259U CPU @ 2.30GHz
Thread count: 4 physical cores, 8 logical processors, using up to 8 threads
Optimize a model with 1 rows, 1 columns and 1 nonzeros
Model fingerprint: 0x3adb76f2
Coefficient statistics:
Matrix range [1e+00, 1e+00]
Objective range [0e+00, 0e+00]
Bounds range [1e+00, 1e+00]
RHS range [0e+00, 0e+00]
Presolve removed 0 rows and 1 columns
Presolve time: 0.00s
Solved in 0 iterations and 0.00 seconds (0.00 work units)
Infeasible model
User-callback calls 19, time in user-callback 0.00 sec
julia> compute_conflict!(model)
IIS computed: 1 constraints and 1 bounds
IIS runtime: 0.00 seconds (0.00 work units)
julia> new_model, ref_map = copy_conflict(model);
julia> print(new_model)
Feasibility
Subject to
c : x ≤ 0.0
x ≥ 1.0
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