[breaking] Fix setting constant objective function (#581)

src/Convex.jl

@@ -218,13 +218,13 @@ for (root, _, files) in walkdir(joinpath(@__DIR__, "constraints"))
     end
 end
 
-include("problems.jl")
 include("SparseTape.jl")
 include("VectorAffineFunctionAsMatrix.jl")
 include("ComplexTape.jl")
 include("operate.jl")
 include("complex_operate.jl")
 include("real_operate.jl")
+include("problems.jl")
 include("solution.jl")
 include("MOI_wrapper.jl")
 

src/MOI_wrapper.jl

@@ -225,12 +225,12 @@ function MOI.supports(
 end
 
 function MOI.set(
-    model::Optimizer,
+    model::Optimizer{T},
     ::MOI.ObjectiveFunction{MOI.ScalarNonlinearFunction},
     func::MOI.ScalarNonlinearFunction,
-)
+) where {T}
     cfp = conic_form!(model.context, _expr(model, func))
-    obj = scalar_fn(cfp)
+    obj = _to_scalar_moi(T, cfp)
     MOI.set(model, MOI.ObjectiveFunction{typeof(obj)}(), obj)
     return
 end

src/problem_depot/problems/lp.jl

@@ -195,7 +195,7 @@ end
     end
     handle_problem!(p)
     if test
-        @test p.optval === nothing
+        @test p.optval === 1.0
         @test evaluate(sum(neg(x))) ≈ 6 atol = atol rtol = rtol
     end
 end

src/problem_depot/problems/sdp.jl

@@ -1499,7 +1499,7 @@ function sdp_quantum_relative_entropy_impl(
                 atol rtol = rtol
         elseif mode == 5
             # Satisfiability problem
-            @test p.optval === nothing
+            @test p.optval ≈ 0 atol = atol rtol = rtol
         end
     end
 end

src/problems.jl

@@ -143,6 +143,20 @@ function new_conic_form!(context::Context, p::Problem)
     return conic_form!(context, p.objective)
 end
 
+function _to_scalar_moi(::Type{T}, x) where {T}
+    return _to_scalar_moi(T, only(MOI.Utilities.scalarize(x)))
+end
+
+function _to_scalar_moi(::Type{T}, x::SparseTape) where {T}
+    return _to_scalar_moi(T, to_vaf(x))
+end
+
+function _to_scalar_moi(::Type{T}, x::Number) where {T<:Real}
+    return MOI.ScalarAffineFunction{T}(MOI.ScalarAffineTerm{T}[], x)
+end
+
+_to_scalar_moi(::Type{T}, f::MOI.AbstractScalarFunction) where {T} = f
+
 function Context(p::Problem{T}, optimizer_factory) where {T}
     context = Context{T}(optimizer_factory)
     cfp = conic_form!(context, p)
@@ -153,7 +167,7 @@ function Context(p::Problem{T}, optimizer_factory) where {T}
     if p.head == :satisfy
         MOI.set(context.model, MOI.ObjectiveSense(), MOI.FEASIBILITY_SENSE)
     else
-        obj = scalar_fn(cfp)
+        obj = _to_scalar_moi(T, cfp)
         MOI.set(context.model, MOI.ObjectiveFunction{typeof(obj)}(), obj)
         MOI.set(
             context.model,
@@ -189,16 +203,20 @@ function minimize(
     return Problem{numeric_type}(:minimize, objective, constraints)
 end
 
-function minimize(::Value, constraints::Constraint...; numeric_type = Float64)
-    return satisfy(collect(constraints); numeric_type = numeric_type)
+function minimize(
+    objective::Value,
+    constraints::Constraint...;
+    numeric_type = Float64,
+)
+    return minimize(objective, collect(constraints); numeric_type)
 end
 
 function minimize(
-    ::Value,
+    objective::Value,
     constraints::Array{<:Constraint} = Constraint[];
     numeric_type = Float64,
 )
-    return satisfy(constraints; numeric_type = numeric_type)
+    return minimize(constant(objective), constraints; numeric_type)
 end
 
 # Allow users to simply type maximize
@@ -218,16 +236,20 @@ function maximize(
     return Problem{numeric_type}(:maximize, objective, constraints)
 end
 
-function maximize(::Value, constraints::Constraint...; numeric_type = Float64)
-    return satisfy(collect(constraints); numeric_type = numeric_type)
+function maximize(
+    objective::Value,
+    constraints::Constraint...;
+    numeric_type = Float64,
+)
+    return maximize(objective, collect(constraints); numeric_type)
 end
 
 function maximize(
-    ::Value,
+    objective::Value,
     constraints::Array{<:Constraint} = Constraint[];
     numeric_type = Float64,
 )
-    return satisfy(constraints; numeric_type = numeric_type)
+    return maximize(constant(objective), constraints; numeric_type)
 end
 
 # Allow users to simply type satisfy (if there is no objective)

src/solution.jl

@@ -10,11 +10,6 @@ function add_variables!(model, var::AbstractVariable)
     end
 end
 
-scalar_fn(x::Number) = x # for `satisfy` problems? Not sure...
-scalar_fn(x) = only(MOI.Utilities.scalarize(x))
-scalar_fn(x::SparseTape) = scalar_fn(to_vaf(x))
-scalar_fn(v::MOI.AbstractScalarFunction) = v
-
 """
     solve!(problem::Problem, optimizer_factory;
         silent_solver = false,

test/test_utilities.jl

@@ -90,18 +90,12 @@ function test_complex_objective_function_errors()
     return
 end
 
-function test_constant_objective()
+function test_satisfy_constant_objective()
     x = Variable()
-    for p in [
-        satisfy(x == 0, x == 1),
-        satisfy(Constraint[]),
-        minimize(0, x == 0),
-        minimize(0, Constraint[]),
-        maximize(0, x == 0),
-        maximize(0, Constraint[]),
-    ]
-        @test isnothing(p.objective)
-    end
+    p = satisfy(x == 0, x == 1)
+    @test isnothing(p.objective)
+    p = satisfy(Constraint[])
+    @test isnothing(p.objective)
     return
 end
 
@@ -1142,6 +1136,55 @@ function test_tree_interface()
     return
 end
 
+function test_scalar_fn_constant_objective()
+    x = Variable()
+    p = minimize(2.1, [x >= 1])
+    solve!(p, SCS.Optimizer; silent_solver = true)
+    @test isapprox(p.optval, 2.1; atol = 1e-5)
+    p = minimize(2.2, x >= 1)
+    solve!(p, SCS.Optimizer; silent_solver = true)
+    @test isapprox(p.optval, 2.2; atol = 1e-5)
+    p = maximize(2.3, [x >= 1])
+    solve!(p, SCS.Optimizer; silent_solver = true)
+    @test isapprox(p.optval, 2.3; atol = 1e-5)
+    p = maximize(2.4, x >= 1)
+    solve!(p, SCS.Optimizer; silent_solver = true)
+    @test isapprox(p.optval, 2.4; atol = 1e-5)
+    return
+end
+
+function test_scalar_fn_objective_number()
+    x = Variable()
+    p = minimize(constant(2), [x >= 1])
+    solve!(p, SCS.Optimizer)
+    @test isapprox(p.optval, 2.0; atol = 1e-5)
+    return
+end
+
+function test_scalar_fn_objective_variable()
+    x = Variable()
+    p = minimize(x, [x >= 1])
+    solve!(p, SCS.Optimizer)
+    @test isapprox(p.optval, 1.0; atol = 1e-5)
+    return
+end
+
+function test_scalar_fn_objective_affine()
+    x = Variable()
+    p = minimize(x + 1, [x >= 1])
+    solve!(p, SCS.Optimizer)
+    @test isapprox(p.optval, 2.0; atol = 1e-5)
+    return
+end
+
+function test_scalar_fn_objective_square()
+    x = Variable()
+    p = minimize(square(x - 2), [x >= 1])
+    solve!(p, SCS.Optimizer)
+    @test isapprox(p.optval, 0.0; atol = 1e-3)
+    return
+end
+
 end  # TestUtilities
 
 TestUtilities.runtests()