Modifications

Constraint Function

modify(model::ModelLike, ci::ConstraintIndex, change::AbstractFunctionModification)

Apply the modification specified by change to the function of constraint ci.

An ModifyConstraintNotAllowed error is thrown if modifying constraints is not supported by the model model.

Examples

modify(model, ci, ScalarConstantChange(10.0))

Objective Function

modify(model::ModelLike, ::ObjectiveFunction, change::AbstractFunctionModification)

Apply the modification specified by change to the objective function of model. To change the function completely, call set instead.

An ModifyObjectiveNotAllowed error is thrown if modifying objectives is not supported by the model model.

Examples

modify(model, ObjectiveFunction{ScalarAffineFunction{Float64}}(), ScalarConstantChange(10.0))

Multiple modifications in Constraint Functions

modify(
    model::ModelLike,
    cis::AbstractVector{<:ConstraintIndex},
    changes::AbstractVector{<:AbstractFunctionModification},
)

Apply multiple modifications specified by changes to the functions of constraints cis.

A ModifyConstraintNotAllowed error is thrown if modifying constraints is not supported by model.

Examples

modify(
    model,
    [ci, ci],
    [
        ScalarCoefficientChange{Float64}(VariableIndex(1), 1.0),
        ScalarCoefficientChange{Float64}(VariableIndex(2), 0.5),
    ],
)

Multiple modifications in the Objective Function

modify(
    model::ModelLike,
    attr::ObjectiveFunction,
    changes::AbstractVector{<:AbstractFunctionModification},
)

Apply multiple modifications specified by changes to the functions of constraints cis.

A ModifyObjectiveNotAllowed error is thrown if modifying objective coefficients is not supported by model.

Examples

modify(
    model,
    ObjectiveFunction{ScalarAffineFunction{Float64}}(),
    [
        ScalarCoefficientChange{Float64}(VariableIndex(1), 1.0),
        ScalarCoefficientChange{Float64}(VariableIndex(2), 0.5),
    ],
)

AbstractFunctionModification

An abstract supertype for structs which specify partial modifications to functions, to be used for making small modifications instead of replacing the functions entirely.

ScalarConstantChange{T}(new_constant::T)

A struct used to request a change in the constant term of a scalar-valued function.

Applicable to ScalarAffineFunction and ScalarQuadraticFunction.

VectorConstantChange{T}(new_constant::Vector{T})

A struct used to request a change in the constant vector of a vector-valued function.

Applicable to VectorAffineFunction and VectorQuadraticFunction.

ScalarCoefficientChange{T}(variable::VariableIndex, new_coefficient::T)

A struct used to request a change in the linear coefficient of a single variable in a scalar-valued function.

Applicable to ScalarAffineFunction and ScalarQuadraticFunction.

ScalarQuadraticCoefficientChange{T}(
    variable_1::VariableIndex,
    variable_2::VariableIndex,
    new_coefficient::T,
)

A struct used to request a change in the quadratic coefficient of a ScalarQuadraticFunction.

Scaling factors

A ScalarQuadraticFunction has an implicit 0.5 scaling factor in front of the Q matrix. This modification applies to terms in the Q matrix.

If variable_1 == variable_2, this modification sets the corresponding diagonal element of the Q matrix to new_coefficient.

If variable_1 != variable_2, this modification is equivalent to setting both the corresponding upper- and lower-triangular elements of the Q matrix to new_coefficient.

As a consequence:

• to modify the term x^2 to become 2x^2, new_coefficient must be 4
• to modify the term xy to become 2xy, new_coefficient must be 2

MultirowChange{T}(
    variable::VariableIndex,
    new_coefficients::Vector{Tuple{Int64,T}},
) where {T}

A struct used to request a change in the linear coefficients of a single variable in a vector-valued function.

New coefficients are specified by (output_index, coefficient) tuples.

Applicable to VectorAffineFunction and VectorQuadraticFunction.