Fix certificate generation with empty constraint matrix (#188)

* Fix certificate generation with empty constraint matrix

* Update infeasibility_certificates.jl

Project.toml

@@ -1,7 +1,7 @@
 name = "GLPK"
 uuid = "60bf3e95-4087-53dc-ae20-288a0d20c6a6"
 repo = "https://github.com/jump-dev/GLPK.jl.git"
-version = "0.14.11"
+version = "0.14.12"
 
 [deps]
 BinaryProvider = "b99e7846-7c00-51b0-8f62-c81ae34c0232"

src/MOI_wrapper/infeasibility_certificates.jl

@@ -24,6 +24,9 @@ found.
 Assumes `ray` has been initialized to all `0.0`s.
 """
 function _get_infeasibility_ray(model::Optimizer, ray::Vector{Float64})
+    if glp_get_num_nz(model) == 0
+        return false  # GLPK aborts if you try to factorize an empty problem.
+    end
     m = glp_get_num_rows(model)
     n = glp_get_num_cols(model)
     @assert length(ray) == m
@@ -74,6 +77,9 @@ Assumes the primal has been solved with primal simplex and is proven unbounded.
 Assumes `ray` has been initialized to all `0.0`s.
 """
 function _get_unbounded_ray(model::Optimizer, ray::Vector{Float64})
+    if glp_get_num_nz(model) == 0
+        return false  # GLPK aborts if you try to factorize an empty problem.
+    end
     m = glp_get_num_rows(model)
     n = glp_get_num_cols(model)
     @assert length(ray) == n

test/MOI_wrapper.jl

@@ -818,3 +818,39 @@ end
     MOI.optimize!(model)
     @test MOI.get(model, MOI.TerminationStatus()) == MOI.OPTIMAL
 end
+
+@testset "empty_problem_infeasible" begin
+    model = GLPK.Optimizer()
+    x = MOI.add_variable(model)
+    MOI.add_constraint(
+        model,
+        MOI.ScalarAffineFunction([MOI.ScalarAffineTerm(0.0, x)], 0.0),
+        MOI.GreaterThan(1.0),
+    )
+    MOI.add_constraint(
+        model,
+        MOI.ScalarAffineFunction([MOI.ScalarAffineTerm(0.0, x)], 0.0),
+        MOI.EqualTo(0.0),
+    )
+    MOI.optimize!(model)
+    @test MOI.get(model, MOI.TerminationStatus()) == MOI.INFEASIBLE
+    @test MOI.get(model, MOI.PrimalStatus()) == MOI.NO_SOLUTION
+    @test MOI.get(model, MOI.DualStatus()) == MOI.NO_SOLUTION
+end
+
+@testset "empty_problem_unbounded" begin
+    model = GLPK.Optimizer()
+    x = MOI.add_variable(model)
+    MOI.add_constraint(
+        model,
+        MOI.ScalarAffineFunction([MOI.ScalarAffineTerm(0.0, x)], 0.0),
+        MOI.EqualTo(0.0),
+    )
+    f = MOI.ScalarAffineFunction([MOI.ScalarAffineTerm(1.0, x)], 0.0)
+    MOI.set(model, MOI.ObjectiveFunction{typeof(f)}(), f)
+    MOI.set(model, MOI.ObjectiveSense(), MOI.MAX_SENSE)
+    MOI.optimize!(model)
+    @test MOI.get(model, MOI.TerminationStatus()) == MOI.DUAL_INFEASIBLE
+    @test MOI.get(model, MOI.PrimalStatus()) == MOI.NO_SOLUTION
+    @test MOI.get(model, MOI.DualStatus()) == MOI.NO_SOLUTION
+end