Missing bridge to ScalarNonlinearFunction in Objective #2833
Description
From Slack:
Constraints from scalar affine / quadratic are accurately bridged to nonlinear. However, for the objective, if a solver only declares support for scalar nonlinear, bridging does not work as expected:
@objective(model, Min, x)ERROR: The solver does not support an objective function of type MathOptInterface.ScalarAffineFunction{Float64}
To illustrate, see the following MWE:
import MathOptInterface as MOI
using JuMP
mutable struct Optimizer <: MOI.AbstractOptimizer
end
function MOI.supports(
::Optimizer,
::MOI.ObjectiveFunction{MOI.ScalarQuadraticFunction{Float64}},
)
return true
end
function MOI.copy_to(dest::Optimizer, src::MOI.ModelLike)
println(src)
return MOI.IndexMap()
end
MOI.is_empty(::Optimizer) = true
MOI.empty!(::Optimizer) = nothing
MOI.optimize!(::Optimizer) = nothing
model = Model(Optimizer)
@variable(model, x[1:2])
@objective(model, Max, x[1] + x[2])
optimize!(model)
# This works fine, the resulting print statement is:
# Maximize ScalarQuadraticFunction{Float64}:
# 0.0 + 1.0 x[1] + 1.0 x[2]
# Subject to:
# However, this does not work:
function MOI.supports(
::Optimizer,
::MOI.ObjectiveFunction{MOI.ScalarQuadraticFunction{Float64}},
)
return false
end
function MOI.supports(
::Optimizer,
::MOI.ObjectiveFunction{MOI.ScalarNonlinearFunction},
)
return true
end
model = Model(Optimizer)
@variable(model, x[1:2])
@objective(model, Max, x[1] + x[2])
# ERROR: The solver does not support an objective
# function of type MathOptInterface.ScalarAffineFunction{Float64}.
optimize!(model)
# Based on the docs I would expect this to work.
# Also, these functions return true:
MOI.Bridges.Objective.supports_objective_function(
MOI.Bridges.Objective.FunctionConversionBridge{Float64, MOI.ScalarNonlinearFunction},
MOI.ScalarAffineFunction{Float64}
) # returns true
MOI.Bridges.Objective.supports_objective_function(
MOI.Bridges.Objective.FunctionConversionBridge{Float64, MOI.ScalarNonlinearFunction},
MOI.ScalarQuadraticFunction{Float64}
) # returns true