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[Bridges.Constraint] change conversion cost to 0.5 for ScalarAffineFunction #3063

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[Bridges.Constraint] change conversion cost to 0.5 for ScalarAffineFunction #3063

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[Bridges.constraint] change conversion cost to 0.5 for ScalarAffineFu…
odow Aug 23, 2026
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odow Aug 23, 2026
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17 changes: 16 additions & 1 deletion src/Bridges/Constraint/bridges/AbstractFunctionConversionBridge.jl
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Expand Up @@ -275,7 +275,22 @@ function conversion_cost(
::Type{<:MOI.ScalarAffineFunction},
::Type{MOI.VariableIndex},
)
return 1.0
# We want to favor bridges which convert VariableIndex or VectorOfVariables
# into ScalarAffineFunction or VectorAffineFunction.
#
# This is most useful for conic solvers, which often support
# VectorAffineFunction-in-S, but not VectorOfVariables-in-S.
#
# The value in this function controls the cost of the transformation
# VectorOfVariables-in-S -> VectorAffineFunction-in-S. When we had the
# previous cost of `1.0`, there might be an alternative bridge
# VectorOfVariables-in-S -> VectorAffineFunction-in-S2 which also has a cost
# of `1.0`, and so, depending on the order in which we choose bridges, we
# might end up using a more complicated bridge that adds a different set
# type to the model.
#
# This was a practical concern for Hypatia in MathOptInterface.jl#3062.
return 0.5
end

function conversion_cost(
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14 changes: 7 additions & 7 deletions test/Bridges/General/test_lazy_bridge_optimizer.jl
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Expand Up @@ -1150,14 +1150,14 @@ Objective function of type `MOI.ScalarQuadraticFunction{$T}` is not supported an
"""
Bridge graph with 2 variable nodes, 5 constraint nodes and 2 objective nodes.
[1] constrained variables in `MOI.Reals` are bridged (distance 1) by $(MOI.Bridges.Variable.FreeBridge{T}).
[2] constrained variables in `MOI.RotatedSecondOrderCone` are bridged (distance 11) by $(MOI.Bridges.Variable.RSOCtoPSDBridge{T}).
(1) `MOI.ScalarQuadraticFunction{$T}`-in-`MOI.GreaterThan{$T}` constraints are bridged (distance 14) by $(MOI.Bridges.Constraint.QuadtoSOCBridge{T}).
(2) `MOI.VectorAffineFunction{$T}`-in-`MOI.RotatedSecondOrderCone` constraints are bridged (distance 13) by $(MOI.Bridges.Constraint.VectorSlackBridge{T,MOI.VectorAffineFunction{T},MOI.RotatedSecondOrderCone}).
(3) `MOI.VariableIndex`-in-`MOI.EqualTo{$T}` constraints are bridged (distance 1) by $(MOI.Bridges.Constraint.ScalarFunctionizeBridge{T,MOI.EqualTo{T}}).
[2] constrained variables in `MOI.RotatedSecondOrderCone` are bridged (distance 10.5) by $(MOI.Bridges.Variable.RSOCtoPSDBridge{T}).
(1) `MOI.ScalarQuadraticFunction{$T}`-in-`MOI.GreaterThan{$T}` constraints are bridged (distance 13.5) by $(MOI.Bridges.Constraint.QuadtoSOCBridge{T}).
(2) `MOI.VectorAffineFunction{$T}`-in-`MOI.RotatedSecondOrderCone` constraints are bridged (distance 12.5) by $(MOI.Bridges.Constraint.VectorSlackBridge{T,MOI.VectorAffineFunction{T},MOI.RotatedSecondOrderCone}).
(3) `MOI.VariableIndex`-in-`MOI.EqualTo{$T}` constraints are bridged (distance 0.5) by $(MOI.Bridges.Constraint.ScalarFunctionizeBridge{T,MOI.EqualTo{T}}).
(4) `MOI.VectorAffineFunction{$T}`-in-`MOI.Zeros` constraints are bridged (distance 1) by $(MOI.Bridges.Constraint.ScalarizeBridge{T,MOI.ScalarAffineFunction{T},MOI.EqualTo{T}}).
(5) `MOI.ScalarQuadraticFunction{$T}`-in-`MOI.LessThan{$T}` constraints are bridged (distance 14) by $(MOI.Bridges.Constraint.QuadtoSOCBridge{T}).
|1| objective function of type `MOI.ScalarQuadraticFunction{$T}` is bridged (distance 31) by $(MOI.Bridges.Objective.SlackBridge{T,MOI.ScalarQuadraticFunction{T},MOI.ScalarQuadraticFunction{T}}).
|2| objective function of type `MOI.VariableIndex` is bridged (distance 1) by $(MOI.Bridges.Objective.FunctionizeBridge{T,MOI.VariableIndex}).
(5) `MOI.ScalarQuadraticFunction{$T}`-in-`MOI.LessThan{$T}` constraints are bridged (distance 13.5) by $(MOI.Bridges.Constraint.QuadtoSOCBridge{T}).
|1| objective function of type `MOI.ScalarQuadraticFunction{$T}` is bridged (distance 29.5) by $(MOI.Bridges.Objective.SlackBridge{T,MOI.ScalarQuadraticFunction{T},MOI.ScalarQuadraticFunction{T}}).
|2| objective function of type `MOI.VariableIndex` is bridged (distance 0.5) by $(MOI.Bridges.Objective.FunctionizeBridge{T,MOI.VariableIndex}).
""",
)
end
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4 changes: 2 additions & 2 deletions test/Utilities/test_copy.jl
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Expand Up @@ -503,7 +503,7 @@ function test_create_variables_using_supports_add_constrained_variable()
@test MOI.get(
bridged_dest,
MOI.ConstraintBridgingCost{MOI.VectorOfVariables,MOI.Nonpositives}(),
) == 1.0
) == 0.5
@test MOI.supports_add_constrained_variables(bridged_dest, MOI.Zeros)
@test MOI.get(bridged_dest, MOI.VariableBridgingCost{MOI.Zeros}()) == 1.0
@test MOI.supports_constraint(
Expand All @@ -514,7 +514,7 @@ function test_create_variables_using_supports_add_constrained_variable()
@test MOI.get(
bridged_dest,
MOI.ConstraintBridgingCost{MOI.VectorOfVariables,MOI.Zeros}(),
) == 3.0
) == 2.5
index_map = MOI.copy_to(bridged_dest, src)
@test length(dest.constraintIndices) == 6

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