Sienna-Platform · luke-kiernan · May 12, 2026 · May 14, 2026 · May 14, 2026
diff --git a/Project.toml b/Project.toml
@@ -29,7 +29,7 @@ PowerFlowsExt = "PowerFlows"
 [sources]
 InfrastructureSystems = {url = "https://github.com/NREL-Sienna/InfrastructureSystems.jl", rev = "IS4"}
 PowerSystems = {url = "https://github.com/NREL-Sienna/PowerSystems.jl", rev = "psy6"}
-InfrastructureOptimizationModels = {url = "https://github.com/NREL-Sienna/InfrastructureOptimizationModels.jl", rev = "ac/psi-costexp-parambroad-pfslack"}
+InfrastructureOptimizationModels = {url = "https://github.com/Sienna-Platform/InfrastructureOptimizationModels.jl", rev = "lk/flow-sign-trait"}
 
 [compat]
 Dates = "1"

diff --git a/src/ac_transmission_models/AC_branches.jl b/src/ac_transmission_models/AC_branches.jl
@@ -26,7 +26,6 @@ get_parameter_multiplier(::Type{LowerBoundValueParameter}, ::PSY.ACTransmission,
 get_parameter_multiplier(::Type{UpperBoundValueParameter}, ::PSY.ACTransmission, ::Type{<:AbstractBranchFormulation}) = 1.0
 
 # Per-device reactance multiplier (1/get_x(d)) computed inline at add_to_expression! call sites.
-get_variable_multiplier(::Type{PhaseShifterAngle}, ::Type{<:PSY.PhaseShiftingTransformer}, ::Type{PhaseAngleControl}) = 1.0
 
 get_multiplier_value(::Type{<:AbstractDynamicBranchRatingTimeSeriesParameter}, d::PSY.ACTransmission, ::Type{StaticBranch}) = PSY.get_rating(d)
 get_multiplier_value(::Type{<:AbstractDynamicBranchRatingTimeSeriesParameter}, d::PNM.BranchesParallel, ::Type{StaticBranch}) = PNM.get_equivalent_rating(d)

diff --git a/src/core/interfaces.jl b/src/core/interfaces.jl
@@ -83,13 +83,29 @@ end
 
 """
 Get the multiplier for a variable type when adding to an expression.
-Default implementation returns 1.0.
-"""
-get_variable_multiplier(
-    ::Type{<:IS.Optimization.VariableType},
-    ::Type{<:IS.InfrastructureSystemsComponent},
-    ::Type{<:IOM.AbstractDeviceFormulation},
-) = 1.0
+
+Default consults [`IOM.flow_sign`](@ref) on the variable type: variables marked
+`FlowInjection` contribute `+1.0`, `FlowWithdrawal` contributes `-1.0`, and
+`FlowUndirected` falls back to `1.0`. Device-driven sign rules (e.g. anything on `PSY.ElectricLoad`)
+should be expressed as more-specific dispatches that override this default.
+"""
+function get_variable_multiplier(
+    ::Type{V},
+    # second arg is any system component, or `PSY.System` which is a ComponentContainer
+    ::Type{<:Union{IS.InfrastructureSystemsComponent, IS.ComponentContainer}},
+    ::Type,  # could be PowerModel (network) or DeviceFormulation (device)
+) where {V <: IS.Optimization.VariableType}
+    return IOM.multiplier_from_sign(IOM.flow_sign(V))
+end
+
+# Hard-error fallback for variable/device/formulation triples that intentionally
+# have no defined multiplier (must be specialized at the call site). Used by
+# devices like Storage/AGC/Reserve/TwoTerminalHVDC to fail loudly instead of
+# returning NaN, which silently poisons JuMP expressions.
+@noinline _unsupported_multiplier(V, D, F) = error(
+    "get_variable_multiplier not implemented for variable $V on $D under $F. " *
+    "This combination must be specialized.",
+)
 
 """
 Get the multiplier for an expression type based on parameter type.

diff --git a/src/core/variables.jl b/src/core/variables.jl
@@ -101,6 +101,9 @@ Docs abbreviation: ``p^\\text{sl,dn}``
 """
 struct SystemBalanceSlackDown <: VariableType end
 
+IOM.flow_sign(::Type{SystemBalanceSlackUp}) = IOM.FlowInjection
+IOM.flow_sign(::Type{SystemBalanceSlackDown}) = IOM.FlowWithdrawal
+
 """
 Struct to dispatch the creation of Reserve requirement slack variables. Used when there is not reserves in the system to satisfy the requirement.
 
@@ -476,6 +479,9 @@ Docs abbreviation: ``f^\\text{sl,dn}``
 """
 struct InterfaceFlowSlackDown <: VariableType end
 
+IOM.flow_sign(::Type{InterfaceFlowSlackUp}) = IOM.FlowInjection
+IOM.flow_sign(::Type{InterfaceFlowSlackDown}) = IOM.FlowWithdrawal
+
 """
 Struct to dispatch the creation of Slack variables for UpperBoundFeedforward
 
@@ -562,6 +568,8 @@ Struct to dispatch the creation of a variable for pumped power in a hydro pump t
 """
 struct ActivePowerPumpVariable <: VariableType end
 
+IOM.flow_sign(::Type{ActivePowerPumpVariable}) = IOM.FlowWithdrawal
+
 """
 Auxiliary Variable for Hydro Models that solve for total energy output
 

diff --git a/src/energy_storage_models/storage_models.jl b/src/energy_storage_models/storage_models.jl
@@ -1,7 +1,7 @@
 #! format: off
 requires_initialization(::AbstractStorageFormulation) = false
 
-get_variable_multiplier(::Type{<:VariableType}, ::Type{<:PSY.Storage}, ::Type{<:AbstractStorageFormulation}) = NaN
+get_variable_multiplier(::Type{V}, ::Type{D}, ::Type{F}) where {V <: VariableType, D <: PSY.Storage, F <: AbstractStorageFormulation} = _unsupported_multiplier(V, D, F)
 ########################### ActivePowerInVariable, Storage #################################
 get_variable_binary(::Type{ActivePowerInVariable}, ::Type{<:PSY.Storage}, ::Type{<:AbstractStorageFormulation}) = false
 get_variable_lower_bound(::Type{ActivePowerInVariable}, d::PSY.Storage, ::Type{<:AbstractStorageFormulation}) = 0.0
@@ -431,63 +431,63 @@ function add_variables!(
 end
 
 ############################# Expression Logic for Ancillary Services ######################
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableCharge},
     ::Type{ReserveAssignmentBalanceDownCharge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveUp},
 ) = 0.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableCharge},
     ::Type{ReserveAssignmentBalanceDownCharge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveDown},
 ) = 1.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableCharge},
     ::Type{ReserveAssignmentBalanceUpCharge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveUp},
 ) = 1.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableCharge},
     ::Type{ReserveAssignmentBalanceUpCharge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveDown},
 ) = 0.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableDischarge},
     ::Type{ReserveAssignmentBalanceDownDischarge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveUp},
 ) = 0.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableDischarge},
     ::Type{ReserveAssignmentBalanceDownDischarge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveDown},
 ) = 1.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableDischarge},
     ::Type{ReserveAssignmentBalanceUpDischarge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveUp},
 ) = 1.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableDischarge},
     ::Type{ReserveAssignmentBalanceUpDischarge},
     d::PSY.Storage,
@@ -496,63 +496,63 @@ get_variable_multiplier(
 ) = 0.0
 
 ### Deployment ###
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableCharge},
     ::Type{ReserveDeploymentBalanceDownCharge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveUp},
 ) = 0.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableCharge},
     ::Type{ReserveDeploymentBalanceDownCharge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveDown},
 ) = 1.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableCharge},
     ::Type{ReserveDeploymentBalanceUpCharge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveUp},
 ) = 1.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableCharge},
     ::Type{ReserveDeploymentBalanceUpCharge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveDown},
 ) = 0.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableDischarge},
     ::Type{ReserveDeploymentBalanceDownDischarge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveUp},
 ) = 0.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableDischarge},
     ::Type{ReserveDeploymentBalanceDownDischarge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveDown},
 ) = 1.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableDischarge},
     ::Type{ReserveDeploymentBalanceUpDischarge},
     d::PSY.Storage,
     ::Type{StorageDispatchWithReserves},
     ::PSY.Reserve{PSY.ReserveUp},
 ) = 1.0
 
-get_variable_multiplier(
+get_reserve_balance_factor(
     ::Type{AncillaryServiceVariableDischarge},
     ::Type{ReserveDeploymentBalanceUpDischarge},
     d::PSY.Storage,
@@ -631,7 +631,7 @@ function add_to_expression!(
         for s in services
             s_name = PSY.get_name(s)
             variable = get_variable(container, U, V, "$(typeof(s))_$s_name")
-            mult = get_variable_multiplier(U, T, d, W, s) * get_fraction(T, s)
+            mult = get_reserve_balance_factor(U, T, d, W, s) * get_fraction(T, s)
             for t in get_time_steps(container)
                 add_proportional_to_jump_expression!(
                     expression[name, t],
@@ -663,7 +663,7 @@ function add_to_expression!(
         for s in services
             s_name = PSY.get_name(s)
             variable = get_variable(container, U, V, "$(typeof(s))_$s_name")
-            mult = get_variable_multiplier(U, T, d, W, s) * get_fraction(T, s)
+            mult = get_reserve_balance_factor(U, T, d, W, s) * get_fraction(T, s)
             for t in get_time_steps(container)
                 add_proportional_to_jump_expression!(
                     expression[name, t],

diff --git a/src/mt_hvdc_models/HVDCsystems.jl b/src/mt_hvdc_models/HVDCsystems.jl
@@ -3,7 +3,6 @@ get_variable_binary(::Type{ActivePowerVariable}, ::Type{PSY.InterconnectingConve
 get_variable_warm_start_value(::Type{ActivePowerVariable}, d::PSY.InterconnectingConverter, ::Type{<:AbstractConverterFormulation}) = PSY.get_active_power(d)
 get_variable_lower_bound(::Type{ActivePowerVariable}, d::PSY.InterconnectingConverter, ::Type{<:AbstractConverterFormulation}) = PSY.get_active_power_limits(d).min
 get_variable_upper_bound(::Type{ActivePowerVariable}, d::PSY.InterconnectingConverter, ::Type{<:AbstractConverterFormulation}) = PSY.get_active_power_limits(d).max
-get_variable_multiplier(::Type{<:VariableType}, ::Type{PSY.InterconnectingConverter}, ::Type{<:AbstractConverterFormulation}) = 1.0
 
 
 function _get_flow_bounds(d::PSY.TModelHVDCLine)
@@ -65,7 +64,6 @@ function get_variable_upper_bound(::Type{DCLineCurrent}, d::PSY.TModelHVDCLine,
     max_v = max(PSY.get_magnitude(bus_from), PSY.get_magnitude(bus_to))
     return p_max_flow / max_v
 end
-get_variable_multiplier(::Type{<:VariableType}, ::Type{PSY.TModelHVDCLine}, ::Type{<:AbstractBranchFormulation}) = 1.0
 
 requires_initialization(::AbstractConverterFormulation) = false
 requires_initialization(::LosslessLine) = false

diff --git a/src/network_models/network_slack_variables.jl b/src/network_models/network_slack_variables.jl
@@ -1,10 +1,3 @@
-#! format: off
-get_variable_multiplier(::Type{SystemBalanceSlackUp}, ::Type{<: Union{PSY.ACBus, PSY.Area, PSY.System}}, ::Type{<:AbstractDeviceFormulation}) = 1.0
-get_variable_multiplier(::Type{SystemBalanceSlackDown}, ::Type{<: Union{PSY.ACBus, PSY.Area, PSY.System}}, ::Type{<:AbstractDeviceFormulation}) = -1.0
-get_variable_multiplier(::Type{SystemBalanceSlackUp}, ::Type{<: Union{PSY.ACBus, PSY.Area, PSY.System}}, ::Type{<:AbstractPowerModel}) = 1.0
-get_variable_multiplier(::Type{SystemBalanceSlackDown}, ::Type{<: Union{PSY.ACBus, PSY.Area, PSY.System}}, ::Type{<:AbstractPowerModel}) = -1.0
-#! format: on
-
 function add_variables!(
     container::OptimizationContainer,
     ::Type{T},

diff --git a/src/services_models/agc.jl b/src/services_models/agc.jl
@@ -1,5 +1,5 @@
 #! format: off
-get_variable_multiplier(::Type{<:VariableType}, ::Type{<:PSY.AGC}, ::Type{<:AbstractAGCFormulation}) = NaN
+get_variable_multiplier(::Type{V}, ::Type{D}, ::Type{F}) where {V <: VariableType, D <: PSY.AGC, F <: AbstractAGCFormulation} = _unsupported_multiplier(V, D, F)
 ########################## ActivePowerVariable, AGC ###########################
 
 ########################## SteadyStateFrequencyDeviation ##################################

diff --git a/src/services_models/reserves.jl b/src/services_models/reserves.jl
@@ -1,7 +1,7 @@
 #! format: off
 ############################### Reserve Variables #########################################
 
-get_variable_multiplier(::Type{<:VariableType}, ::Type{<:PSY.Reserve}, ::Type{<:AbstractReservesFormulation}) = NaN
+get_variable_multiplier(::Type{V}, ::Type{D}, ::Type{F}) where {V <: VariableType, D <: PSY.Reserve, F <: AbstractReservesFormulation} = _unsupported_multiplier(V, D, F)
 ############################### PostContingencyActivePowerReserveDeploymentVariable, Reserve #########################################
 get_variable_binary(::Type{PostContingencyActivePowerReserveDeploymentVariable}, ::Type{<:PSY.Reserve}, ::Type{<:AbstractSecurityConstrainedReservesFormulation}) = false
 function get_variable_upper_bound(::Type{PostContingencyActivePowerReserveDeploymentVariable}, r::PSY.Reserve, d::PSY.Device, ::Type{<:AbstractSecurityConstrainedReservesFormulation})

diff --git a/src/services_models/transmission_interface.jl b/src/services_models/transmission_interface.jl
@@ -3,12 +3,6 @@ get_variable_binary(::Type{<:VariableType}, ::Type{PSY.TransmissionInterface}, :
 get_variable_lower_bound(::Type{InterfaceFlowSlackUp}, ::PSY.TransmissionInterface, ::Type{ConstantMaxInterfaceFlow}) = 0.0
 get_variable_lower_bound(::Type{InterfaceFlowSlackDown}, ::PSY.TransmissionInterface, ::Type{ConstantMaxInterfaceFlow}) = 0.0
 
-get_variable_multiplier(::Type{InterfaceFlowSlackUp}, ::Type{PSY.TransmissionInterface}, ::Type{ConstantMaxInterfaceFlow}) = 1.0
-get_variable_multiplier(::Type{InterfaceFlowSlackDown}, ::Type{PSY.TransmissionInterface}, ::Type{ConstantMaxInterfaceFlow}) = -1.0
-
-get_variable_multiplier(::Type{InterfaceFlowSlackUp}, ::Type{PSY.TransmissionInterface}, ::Type{VariableMaxInterfaceFlow}) = 1.0
-get_variable_multiplier(::Type{InterfaceFlowSlackDown}, ::Type{PSY.TransmissionInterface}, ::Type{VariableMaxInterfaceFlow}) = -1.0
-
 get_multiplier_value(::Type{MinInterfaceFlowLimitParameter}, d::PSY.TransmissionInterface, ::Type{VariableMaxInterfaceFlow}) = PSY.get_min_active_power_flow_limit(d)
 get_multiplier_value(::Type{MaxInterfaceFlowLimitParameter}, d::PSY.TransmissionInterface, ::Type{VariableMaxInterfaceFlow}) = PSY.get_max_active_power_flow_limit(d)
 

diff --git a/src/static_injector_models/hydro_generation.jl b/src/static_injector_models/hydro_generation.jl
@@ -4,8 +4,6 @@
 requires_initialization(::AbstractHydroReservoirFormulation) = false
 requires_initialization(::AbstractHydroUnitCommitment) = true
 
-get_variable_multiplier(::Type{<:VariableType}, ::Type{<:PSY.HydroGen}, ::Type{<:AbstractHydroFormulation}) = 1.0
-get_variable_multiplier(::Type{ActivePowerPumpVariable}, ::Type{<:PSY.HydroPumpTurbine}, ::Type{<:AbstractHydroPumpFormulation}) = -1.0
 get_expression_type_for_reserve(::Type{ActivePowerReserveVariable}, ::Type{<:PSY.HydroGen}, ::Type{<:PSY.Reserve{PSY.ReserveUp}}) = ActivePowerRangeExpressionUB
 get_expression_type_for_reserve(::Type{ActivePowerReserveVariable}, ::Type{<:PSY.HydroGen}, ::Type{<:PSY.Reserve{PSY.ReserveDown}}) = ActivePowerRangeExpressionLB
 
@@ -36,13 +34,11 @@ get_variable_upper_bound(::Type{EnergyVariable}, d::PSY.HydroGen, ::Type{<:Abstr
 get_variable_binary(::Type{ActivePowerInVariable}, ::Type{<:PSY.HydroGen}, ::Type{<:AbstractHydroReservoirFormulation}) = false
 get_variable_lower_bound(::Type{ActivePowerInVariable}, d::PSY.HydroGen, ::Type{<:AbstractHydroReservoirFormulation}) = 0.0
 get_variable_upper_bound(::Type{ActivePowerInVariable}, d::PSY.HydroGen, ::Type{<:AbstractHydroReservoirFormulation}) = nothing
-get_variable_multiplier(::Type{ActivePowerInVariable}, d::Type{<:PSY.HydroGen}, ::Type{<:AbstractHydroReservoirFormulation}) = -1.0
 
 ########################### ActivePowerOutVariable, HydroGen #################################
 get_variable_binary(::Type{ActivePowerOutVariable}, ::Type{<:PSY.HydroGen}, ::Type{<:AbstractHydroReservoirFormulation}) = false
 get_variable_lower_bound(::Type{ActivePowerOutVariable}, d::PSY.HydroGen, ::Type{<:AbstractHydroReservoirFormulation}) = 0.0
 get_variable_upper_bound(::Type{ActivePowerOutVariable}, d::PSY.HydroGen, ::Type{<:AbstractHydroReservoirFormulation}) = nothing
-get_variable_multiplier(::Type{ActivePowerOutVariable}, d::Type{<:PSY.HydroGen}, ::Type{<:AbstractHydroReservoirFormulation}) = 1.0
 
 ############## OnVariable, HydroGen ####################
 # These methods are defined in PowerSimulations

diff --git a/src/static_injector_models/reactivepower_device.jl b/src/static_injector_models/reactivepower_device.jl
@@ -1,7 +1,6 @@
 #! format: off
 
 requires_initialization(::AbstractReactivePowerDeviceFormulation) = false
-get_variable_multiplier(::Type{<:VariableType}, ::Type{<:PSY.SynchronousCondenser}, ::Type{<:AbstractReactivePowerDeviceFormulation}) = 1.0
 
 ############## ReactivePowerVariable, SynchronousCondensers ####################
 get_variable_binary(::Type{ReactivePowerVariable}, ::Type{PSY.SynchronousCondenser}, ::Type{<:AbstractReactivePowerDeviceFormulation}) = false

diff --git a/src/static_injector_models/renewable_generation.jl b/src/static_injector_models/renewable_generation.jl
@@ -1,5 +1,4 @@
 #! format: off
-get_variable_multiplier(::Type{<:VariableType}, ::Type{<:PSY.RenewableGen}, ::Type{<:AbstractRenewableFormulation}) = 1.0
 get_expression_type_for_reserve(::Type{ActivePowerReserveVariable}, ::Type{<:PSY.RenewableGen}, ::Type{<:PSY.Reserve{PSY.ReserveUp}}) = ActivePowerRangeExpressionUB
 get_expression_type_for_reserve(::Type{ActivePowerReserveVariable}, ::Type{<:PSY.RenewableGen}, ::Type{<:PSY.Reserve{PSY.ReserveDown}}) = ActivePowerRangeExpressionLB
 ########################### ActivePowerVariable, RenewableGen #################################

diff --git a/src/static_injector_models/source.jl b/src/static_injector_models/source.jl
@@ -3,9 +3,6 @@
 requires_initialization(::ImportExportSourceModel) = false
 
 
-get_variable_multiplier(::Type{ActivePowerOutVariable}, ::Type{<:PSY.Source}, ::Type{<:AbstractSourceFormulation}) = 1.0
-get_variable_multiplier(::Type{ActivePowerInVariable}, ::Type{<:PSY.Source}, ::Type{<:AbstractSourceFormulation}) = -1.0
-get_variable_multiplier(::Type{ReactivePowerVariable}, ::Type{<:PSY.Source}, ::Type{<:AbstractSourceFormulation}) = 1.0
 ############## ActivePowerVariables, Source ####################
 get_variable_binary(::Type{ActivePowerInVariable}, ::Type{<:PSY.Source}, ::Type{<:AbstractSourceFormulation}) = false
 get_variable_binary(::Type{ActivePowerOutVariable}, ::Type{<:PSY.Source}, ::Type{<:AbstractSourceFormulation}) = false

diff --git a/src/static_injector_models/thermal_generation.jl b/src/static_injector_models/thermal_generation.jl
@@ -30,9 +30,7 @@ requires_initialization(::ThermalStandardDispatch) = true
 requires_initialization(::ThermalBasicCompactUnitCommitment) = false
 requires_initialization(::ThermalBasicUnitCommitment) = false
 
-get_variable_multiplier(::Type{<:VariableType}, ::Type{<:PSY.ThermalGen}, ::Type{<:AbstractThermalFormulation}) = 1.0
 # Per-device P_min multiplier computed inline at add_to_expression! call sites.
-get_variable_multiplier(::Type{OnVariable}, ::Type{<:PSY.ThermalGen}, ::Type{<:Union{AbstractCompactUnitCommitment, ThermalCompactDispatch}}) = 1.0
 get_expression_type_for_reserve(::Type{ActivePowerReserveVariable}, ::Type{<:PSY.ThermalGen}, ::Type{<:PSY.Reserve{PSY.ReserveUp}}) = ActivePowerRangeExpressionUB
 get_expression_type_for_reserve(::Type{ActivePowerReserveVariable}, ::Type{<:PSY.ThermalGen}, ::Type{<:PSY.Reserve{PSY.ReserveDown}}) = ActivePowerRangeExpressionLB