Trouble fixing variable in linear constraint

[adrien-le-franc]

Hi,

I need to solve a sequence of LP with a changing constant value in a linear constraint. I picked a solution from the doc at http://www.juliaopt.org/JuMP.jl/v0.20.0/constraints/ but I got an error which I could summarize in this example:

using JuMP
using Clp

m = Model(with_optimizer(Clp.Optimizer, LogLevel=0))
@variable(m, 0 <= x)
@variable(m, xmax)
@constraint(m, x <= xmax)
fix(m[:xmax], 1.)
@objective(m, Min, x)
optimize!(m)

this gives:

ERROR: UndefVarError: getconstant not defined
Stacktrace:
 [1] add_linear_constraints(::Clp.Optimizer, ::Array{MathOptInterface.ScalarAffineFunction{Float64},1}, ::Array{MathOptInterface.LessThan{Float64},1}) at /opt/julia/packages/LinQuadOptInterface/ZMx9f/src/constraints/scalaraffine.jl:79
 [2] add_constraints(::Clp.Optimizer, ::Array{MathOptInterface.ScalarAffineFunction{Float64},1}, ::Array{MathOptInterface.LessThan{Float64},1}) at /opt/julia/packages/LinQuadOptInterface/ZMx9f/src/constraints/scalaraffine.jl:62
 [3] add_constraints(::MathOptInterface.Bridges.LazyBridgeOptimizer{Clp.Optimizer}, ::Array{MathOptInterface.ScalarAffineFunction{Float64},1}, ::Array{MathOptInterface.LessThan{Float64},1}) at /opt/julia/packages/MathOptInterface/4hMCx/src/Bridges/bridge_optimizer.jl:1011
 [4] copy_constraints(::MathOptInterface.Bridges.LazyBridgeOptimizer{Clp.Optimizer}, ::MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.Model{Float64}}, ::MathOptInterface.Utilities.IndexMap, ::Array{MathOptInterface.ConstraintIndex{MathOptInterface.ScalarAffineFunction{Float64},MathOptInterface.LessThan{Float64}},1}) at /opt/julia/packages/MathOptInterface/4hMCx/src/Utilities/copy.jl:228
 [5] pass_constraints(::MathOptInterface.Bridges.LazyBridgeOptimizer{Clp.Optimizer}, ::MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.Model{Float64}}, ::Bool, ::MathOptInterface.Utilities.IndexMap, ::Array{DataType,1}, ::Array{Array{T,1} where T,1}, ::Array{DataType,1}, ::Array{Array{T,1} where T,1}, ::typeof(MathOptInterface.Utilities.copy_constraints), ::typeof(MathOptInterface.set)) at /opt/julia/packages/MathOptInterface/4hMCx/src/Utilities/copy.jl:265
 [6] pass_constraints(::MathOptInterface.Bridges.LazyBridgeOptimizer{Clp.Optimizer}, ::MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.Model{Float64}}, ::Bool, ::MathOptInterface.Utilities.IndexMap, ::Array{DataType,1}, ::Array{Array{T,1} where T,1}, ::Array{DataType,1}, ::Array{Array{T,1} where T,1}) at /opt/julia/packages/MathOptInterface/4hMCx/src/Utilities/copy.jl:240
 [7] default_copy_to(::MathOptInterface.Bridges.LazyBridgeOptimizer{Clp.Optimizer}, ::MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.Model{Float64}}, ::Bool) at /opt/julia/packages/MathOptInterface/4hMCx/src/Utilities/copy.jl:340
 [8] #automatic_copy_to#97 at /opt/julia/packages/MathOptInterface/4hMCx/src/Utilities/copy.jl:15 [inlined]
 [9] #automatic_copy_to at ./none:0 [inlined]
 [10] #copy_to#1 at /opt/julia/packages/MathOptInterface/4hMCx/src/Bridges/bridge_optimizer.jl:228 [inlined]
 [11] (::getfield(MathOptInterface, Symbol("#kw##copy_to")))(::NamedTuple{(:copy_names,),Tuple{Bool}}, ::typeof(MathOptInterface.copy_to), ::MathOptInterface.Bridges.LazyBridgeOptimizer{Clp.Optimizer}, ::MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.Model{Float64}}) at ./none:0
 [12] attach_optimizer(::MathOptInterface.Utilities.CachingOptimizer{MathOptInterface.AbstractOptimizer,MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.Model{Float64}}}) at /opt/julia/packages/MathOptInterface/4hMCx/src/Utilities/cachingoptimizer.jl:149
 [13] optimize!(::MathOptInterface.Utilities.CachingOptimizer{MathOptInterface.AbstractOptimizer,MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.Model{Float64}}}) at /opt/julia/packages/MathOptInterface/4hMCx/src/Utilities/cachingoptimizer.jl:185
 [14] #optimize!#78(::Bool, ::Bool, ::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}, ::Function, ::Model, ::Nothing) at /opt/julia/packages/JuMP/iGamg/src/optimizer_interface.jl:141
 [15] optimize! at /opt/julia/packages/JuMP/iGamg/src/optimizer_interface.jl:111 [inlined] (repeats 2 times)
 [16] top-level scope at none:0

I also get this error with CPLEX so it seems solver independent. I am using JuMP v0.20.0 with Julia 1.1.1

I had a look at https://github.com/JuliaOpt/LinQuadOptInterface.jl/blob/master/src/constraints/scalaraffine.jl where the error comes from, not sure wether if it should be a JuMP or LinQuadOptInterface issue

[blegat]

CPLEX and Clp have not yet been updated to JuMP v0.20/MOI v0.9, see jump-dev/MathOptInterface.jl#736 for an up to date list of solvers that have been ported.

[adrien-le-franc]

Thanks for your help, I moved back to JuMP v0.19 until the update. Perhaps CPLEX and Clp should be temporally removed from the list of currently supported solver on the v0.20 documentation

[blegat]

CPLEX and Clp have now been updated thanks to @odow and @mtanneau