[Bridges] add ScalarQuadraticToScalarNonlinearBridge (#2233)

docs/src/submodules/Bridges/list_of_bridges.md

@@ -28,6 +28,7 @@ Bridges.Constraint.ScalarSlackBridge
 Bridges.Constraint.VectorSlackBridge
 Bridges.Constraint.ScalarFunctionizeBridge
 Bridges.Constraint.VectorFunctionizeBridge
+Bridges.Constraint.ScalarQuadraticToScalarNonlinearBridge
 Bridges.Constraint.SplitComplexEqualToBridge
 Bridges.Constraint.SplitComplexZerosBridge
 Bridges.Constraint.SplitHyperRectangleBridge

src/Bridges/Constraint/Constraint.jl

@@ -83,6 +83,10 @@ function add_all_bridges(bridged_model, ::Type{T}) where {T}
     MOI.Bridges.add_bridge(bridged_model, VectorSlackBridge{T})
     MOI.Bridges.add_bridge(bridged_model, ScalarFunctionizeBridge{T})
     MOI.Bridges.add_bridge(bridged_model, VectorFunctionizeBridge{T})
+    MOI.Bridges.add_bridge(
+        bridged_model,
+        ScalarQuadraticToScalarNonlinearBridge{T},
+    )
     MOI.Bridges.add_bridge(bridged_model, SplitHyperRectangleBridge{T})
     MOI.Bridges.add_bridge(bridged_model, SplitIntervalBridge{T})
     MOI.Bridges.add_bridge(bridged_model, SplitComplexEqualToBridge{T})

src/Bridges/Constraint/bridges/functionize.jl

@@ -322,3 +322,102 @@ function MOI.get(
     f = MOI.get(model, attr, b.constraint)
     return MOI.Utilities.convert_approx(MOI.VectorOfVariables, f)
 end
+
+"""
+    ScalarQuadraticToScalarNonlinearBridge{T,S} <: Bridges.Constraint.AbstractBridge
+
+`ScalarQuadraticToScalarNonlinearBridge` implements the following reformulations:
+
+  * ``f(x) \\in S`` into ``g(x) \\in S``
+
+where `f` is a [`MOI.ScalarQuadraticFunction`](@ref) and `g` is a
+[`MOI.ScalarNonlinearFunction{T}`](@ref).
+
+## Source node
+
+`ScalarQuadraticToScalarNonlinearBridge` supports:
+
+  * [`MOI.ScalarQuadraticFunction`](@ref) in `S`
+
+## Target nodes
+
+`ScalarQuadraticToScalarNonlinearBridge` creates:
+
+  * [`MOI.ScalarNonlinearFunction{T}`](@ref) in `S`
+"""
+struct ScalarQuadraticToScalarNonlinearBridge{T,S} <:
+       AbstractFunctionConversionBridge{MOI.ScalarNonlinearFunction,S}
+    constraint::MOI.ConstraintIndex{MOI.ScalarNonlinearFunction,S}
+end
+
+const ScalarQuadraticToScalarNonlinear{T,OT<:MOI.ModelLike} =
+    SingleBridgeOptimizer{ScalarQuadraticToScalarNonlinearBridge{T},OT}
+
+function bridge_constraint(
+    ::Type{ScalarQuadraticToScalarNonlinearBridge{T,S}},
+    model::MOI.ModelLike,
+    f::MOI.ScalarQuadraticFunction{T},
+    s::S,
+) where {T,S}
+    ci = MOI.add_constraint(model, convert(MOI.ScalarNonlinearFunction, f), s)
+    return ScalarQuadraticToScalarNonlinearBridge{T,S}(ci)
+end
+
+function MOI.supports_constraint(
+    ::Type{ScalarQuadraticToScalarNonlinearBridge{T}},
+    ::Type{MOI.ScalarQuadraticFunction{T}},
+    ::Type{<:MOI.AbstractScalarSet},
+) where {T}
+    return true
+end
+
+function MOI.Bridges.added_constrained_variable_types(
+    ::Type{<:ScalarQuadraticToScalarNonlinearBridge},
+)
+    return Tuple{Type}[]
+end
+
+function MOI.Bridges.added_constraint_types(
+    ::Type{ScalarQuadraticToScalarNonlinearBridge{T,S}},
+) where {T,S}
+    return Tuple{Type,Type}[(MOI.ScalarNonlinearFunction, S)]
+end
+
+function concrete_bridge_type(
+    ::Type{<:ScalarQuadraticToScalarNonlinearBridge{T}},
+    ::Type{MOI.ScalarQuadraticFunction{T}},
+    S::Type{<:MOI.AbstractScalarSet},
+) where {T}
+    return ScalarQuadraticToScalarNonlinearBridge{T,S}
+end
+
+function MOI.get(
+    ::ScalarQuadraticToScalarNonlinearBridge{T,S},
+    ::MOI.NumberOfConstraints{MOI.ScalarNonlinearFunction,S},
+)::Int64 where {T,S}
+    return 1
+end
+
+function MOI.get(
+    b::ScalarQuadraticToScalarNonlinearBridge{T,S},
+    ::MOI.ListOfConstraintIndices{MOI.ScalarNonlinearFunction,S},
+) where {T,S}
+    return [b.constraint]
+end
+
+function MOI.delete(
+    model::MOI.ModelLike,
+    c::ScalarQuadraticToScalarNonlinearBridge,
+)
+    MOI.delete(model, c.constraint)
+    return
+end
+
+function MOI.get(
+    model::MOI.ModelLike,
+    ::MOI.ConstraintFunction,
+    b::ScalarQuadraticToScalarNonlinearBridge{T},
+) where {T}
+    f = MOI.get(model, MOI.ConstraintFunction(), b.constraint)
+    return convert(MOI.ScalarQuadraticFunction{T}, f)
+end

src/functions.jl

@@ -900,6 +900,69 @@ function Base.convert(
     return ScalarAffineFunction{T}(f.affine_terms, f.constant)
 end
 
+_order(x::Real, y::VariableIndex) = (x, y)
+_order(x::VariableIndex, y::Real) = (y, x)
+_order(x, y) = nothing
+
+function Base.convert(
+    ::Type{ScalarAffineTerm{T}},
+    f::ScalarNonlinearFunction,
+) where {T}
+    if f.head != :* || length(f.args) != 2
+        throw(InexactError(:convert, ScalarAffineTerm, f))
+    end
+    ret = _order(f.args[1], f.args[2])
+    if ret === nothing
+        throw(InexactError(:convert, ScalarAffineTerm, f))
+    end
+    return ScalarAffineTerm(convert(T, ret[1]), ret[2])
+end
+
+function _add_to_function(
+    f::ScalarAffineFunction{T},
+    arg::Union{Real,VariableIndex,ScalarAffineFunction},
+) where {T}
+    return Utilities.operate!(+, T, f, arg)
+end
+
+function _add_to_function(
+    f::ScalarAffineFunction{T},
+    arg::ScalarNonlinearFunction,
+) where {T}
+    if arg.head == :* && length(arg.args) == 2
+        push!(f.terms, convert(ScalarAffineTerm{T}, arg))
+    else
+        _add_to_function(f, convert(ScalarAffineFunction{T}, arg))
+    end
+    return f
+end
+
+_add_to_function(::ScalarAffineFunction, ::Any) = nothing
+
+# This is a very rough-and-ready conversion function that only works for very
+# basic expressions, such as those created by
+# `convert(ScalarNonlinearFunction, f)`.
+function Base.convert(
+    ::Type{ScalarAffineFunction{T}},
+    f::ScalarNonlinearFunction,
+) where {T}
+    if f.head == :* && length(f.args) == 2
+        term = convert(ScalarAffineTerm{T}, f)
+        return ScalarAffineFunction{T}([term], zero(T))
+    end
+    if f.head != :+
+        throw(InexactError(:convert, ScalarAffineFunction{T}, f))
+    end
+    output = ScalarAffineFunction{T}(ScalarAffineTerm{T}[], zero(T))
+    for arg in f.args
+        output = _add_to_function(output, arg)
+        if output === nothing
+            throw(InexactError(:convert, ScalarAffineFunction{T}, f))
+        end
+    end
+    return output
+end
+
 # ScalarQuadraticFunction
 
 function Base.convert(::Type{ScalarQuadraticFunction{T}}, α::T) where {T}
@@ -949,6 +1012,88 @@ function Base.convert(
     )
 end
 
+_order(x::Real, y::VariableIndex, z::VariableIndex) = (x, y, z)
+_order(x::VariableIndex, y::Real, z::VariableIndex) = (y, x, z)
+_order(x::VariableIndex, y::VariableIndex, z::Real) = (z, x, y)
+_order(x, y, z) = nothing
+
+function Base.convert(
+    ::Type{ScalarQuadraticTerm{T}},
+    f::ScalarNonlinearFunction,
+) where {T}
+    if f.head != :* || length(f.args) != 3
+        throw(InexactError(:convert, ScalarQuadraticTerm, f))
+    end
+    ret = _order(f.args[1], f.args[2], f.args[3])
+    if ret === nothing
+        throw(InexactError(:convert, ScalarQuadraticTerm, f))
+    end
+    coef = convert(T, ret[1])
+    if ret[2] == ret[3]
+        coef *= 2
+    end
+    return ScalarQuadraticTerm(coef, ret[2], ret[3])
+end
+
+function _add_to_function(
+    f::ScalarQuadraticFunction{T},
+    arg::Union{Real,VariableIndex,ScalarAffineFunction,ScalarQuadraticFunction},
+) where {T}
+    return Utilities.operate!(+, T, f, arg)
+end
+
+function _add_to_function(
+    f::ScalarQuadraticFunction{T},
+    arg::ScalarNonlinearFunction,
+) where {T}
+    if arg.head == :* && length(arg.args) == 2
+        push!(f.affine_terms, convert(ScalarAffineTerm{T}, arg))
+    elseif arg.head == :* && length(arg.args) == 3
+        push!(f.quadratic_terms, convert(ScalarQuadraticTerm{T}, arg))
+    else
+        _add_to_function(f, convert(ScalarQuadraticFunction{T}, arg))
+    end
+    return f
+end
+
+# This is a very rough-and-ready conversion function that only works for very
+# basic expressions, such as those created by
+# `convert(ScalarNonlinearFunction, f)`.
+function Base.convert(
+    ::Type{ScalarQuadraticFunction{T}},
+    f::ScalarNonlinearFunction,
+) where {T}
+    if f.head == :*
+        if length(f.args) == 2
+            quad_terms = ScalarQuadraticTerm{T}[]
+            affine_terms = [convert(ScalarAffineTerm{T}, f)]
+            return ScalarQuadraticFunction{T}(quad_terms, affine_terms, zero(T))
+        elseif length(f.args) == 3
+            quad_terms = [convert(ScalarQuadraticTerm{T}, f)]
+            affine_terms = ScalarAffineTerm{T}[]
+            return ScalarQuadraticFunction{T}(quad_terms, affine_terms, zero(T))
+        end
+    elseif f.head == :^ && length(f.args) == 2 && f.args[2] == 2
+        return convert(
+            ScalarQuadraticFunction{T},
+            ScalarNonlinearFunction(:*, Any[one(T), f.args[1], f.args[1]]),
+        )
+    end
+    if f.head != :+
+        throw(InexactError(:convert, ScalarQuadraticFunction{T}, f))
+    end
+    output = ScalarQuadraticFunction(
+        ScalarQuadraticTerm{T}[],
+        ScalarAffineTerm{T}[],
+        zero(T),
+    )
+    for arg in f.args
+        # Unlike ScalarAffineFunction, _add_to_function cannot return ::Nothing
+        output = _add_to_function(output, arg)::ScalarQuadraticFunction{T}
+    end
+    return output
+end
+
 # ScalarNonlinearFunction
 
 function Base.convert(::Type{ScalarNonlinearFunction}, term::ScalarAffineTerm)

test/Bridges/Constraint/functionize.jl

@@ -293,6 +293,21 @@ function test_runtests()
     return
 end
 
+function test_scalar_quadratic_to_nonlinear()
+    MOI.Bridges.runtests(
+        MOI.Bridges.Constraint.ScalarQuadraticToScalarNonlinearBridge,
+        """
+        variables: x, y
+        1.0 * x * x + 2.0 * x * y + 3.0 * y + 4.0 >= 1.0
+        """,
+        """
+        variables: x, y
+        ScalarNonlinearFunction(1.0 * x * x + 2.0 * x * y + 3.0 * y + 4.0) >= 1.0
+        """,
+    )
+    return
+end
+
 end  # module
 
 TestConstraintFunctionize.runtests()