Bug modifying coefficient after constraint deletion

[odow]

Found by someone at UoA. If I find their GitHub handle, I'll edit here.

julia> using Gurobi

julia> import MathOptInterface as MOI

julia> model = Gurobi.Optimizer()
    sense  : minimize
    number of variables             = 0
    number of linear constraints    = 0
    number of quadratic constraints = 0
    number of sos constraints       = 0
    number of non-zero coeffs       = 0
    number of non-zero qp objective terms  = 0
    number of non-zero qp constraint terms = 0


julia> x = MOI.add_variable(model)
MOI.VariableIndex(1)

julia> c = [MOI.add_constraint(model, i * x, MOI.LessThan(i)) for i in [1.0, 2.0]]
2-element Vector{MathOptInterface.ConstraintIndex{MathOptInterface.ScalarAffineFunction{Float64}, MathOptInterface.LessThan{Float64}}}:
 MathOptInterface.ConstraintIndex{MathOptInterface.ScalarAffineFunction{Float64}, MathOptInterface.LessThan{Float64}}(2)
 MathOptInterface.ConstraintIndex{MathOptInterface.ScalarAffineFunction{Float64}, MathOptInterface.LessThan{Float64}}(3)

julia> MOI.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 2 rows, 1 columns and 2 nonzeros
Model fingerprint: 0x04ae1447
Coefficient statistics:
  Matrix range     [1e+00, 2e+00]
  Objective range  [0e+00, 0e+00]
  Bounds range     [0e+00, 0e+00]
  RHS range        [1e+00, 2e+00]
Presolve removed 2 rows and 1 columns
Presolve time: 0.00s
Presolve: All rows and columns removed
Iteration    Objective       Primal Inf.    Dual Inf.      Time
       0    0.0000000e+00   0.000000e+00   0.000000e+00      0s

Solved in 0 iterations and 0.00 seconds (0.00 work units)
Optimal objective  0.000000000e+00

User-callback calls 31, time in user-callback 0.00 sec

julia> MOI.delete(model, c[1])

julia> MOI.modify(model, c[2], MOI.ScalarCoefficientChange(x, 4.0))

julia> MOI.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: 0x742efd99
Coefficient statistics:
  Matrix range     [2e+00, 2e+00]
  Objective range  [0e+00, 0e+00]
  Bounds range     [0e+00, 0e+00]
  RHS range        [2e+00, 2e+00]
Presolve removed 1 rows and 1 columns
Presolve time: 0.00s
Presolve: All rows and columns removed
Iteration    Objective       Primal Inf.    Dual Inf.      Time
       0    0.0000000e+00   0.000000e+00   0.000000e+00      0s

Solved in 0 iterations and 0.00 seconds (0.00 work units)
Optimal objective  0.000000000e+00

User-callback calls 31, time in user-callback 0.00 sec

julia> GRBwrite(model, "bug.lp")
0

julia> print(read("bug.lp", String))
\ LP format - for model browsing. Use MPS format to capture full model detail.
Minimize
 
Subject To
 R1: 2 C0 <= 2
Bounds
 C0 free
End

R1 should be 4 C0 <= 2

[odow]

Here's a C example:

julia> using Gurobi

julia> p_env = Ref{Ptr{Cvoid}}()
Base.RefValue{Ptr{Nothing}}(Ptr{Nothing} @0x0000000141e19590)

julia> GRBemptyenv(p_env)
0

julia> env = p_env[]
Ptr{Nothing} @0x00007ff5bf081800

julia> GRBstartenv(env)
0

julia> p_model = Ref{Ptr{Cvoid}}()
Base.RefValue{Ptr{Nothing}}(Ptr{Nothing} @0x000000010c432b90)

julia> GRBnewmodel(env, p_model, "", 0, C_NULL, C_NULL, C_NULL, C_NULL, C_NULL)
0

julia> model = p_model[]
Ptr{Nothing} @0x00007ff5afe4a9a0

julia> GRBaddvar(model, 0, C_NULL, C_NULL, 0.0, -Inf, Inf, GRB_CONTINUOUS, "")
0

julia> GRBaddconstr(model, 1, Cint[0], [1.0], Cchar('<'), 1.0, "")
0

julia> GRBaddconstr(model, 1, Cint[0], [2.0], Cchar('<'), 2.0, "")
0

julia> GRBdelconstrs(model, 1, Cint[0])
0

julia> nothing # GRBupdatemodel(model)

julia> GRBchgcoeffs(model, 1, Cint[0], Cint[0], [3.0])
0

julia> GRBwrite(model, "bug.lp")
0

julia> print(read("bug.lp", String))
\ LP format - for model browsing. Use MPS format to capture full model detail.
Minimize
 
Subject To
 R1: 2 C0 <= 2
Bounds
 C0 free
End