Procedure GMP::Solution::SetColumnValue(GMP, solution, column, value, valueType)

GMP::Solution::SetColumnValue

The procedure GMP::Solution::SetColumnValue sets the level value, reduced cost, hint value or hint priority of a column in a solution in the solution repository of a generated mathematical program.
Hint values and hint priorities can be used as follows: If you know that a variable is likely to take a particular value in high quality solutions of a MIP model, you can provide that value as a hint. You can also (optionally) provide a hint priority which resembles your level of confidence in a hint.
GMP::Solution::SetColumnValue(
     GMP,            ! (input) a generated mathematical program
     solution,       ! (input) a solution
     column,         ! (input) a scalar reference or column number
     value,          ! (input) a scalar value
     [valueType]     ! (input/optional) a scalar value
     )

Arguments

GMP

An element in AllGeneratedMathematicalPrograms.

solution

An integer scalar reference to a solution.

column

A scalar reference to an existing column in the matrix or the number of that column in the range \(\{ 0 .. n-1 \}\) where \(n\) is the number of columns in the matrix.

value

The value to be assigned to the column.

valueType

A scalar value specifying the value type. If 0 (the default) then the level value will be set. If 1, the reduced cost. If 2, the hint value, and if 3 the hint priority.

Return Value

The procedure returns 1 on success, or 0 otherwise.

Note

  • If the column has a unit then the scaled value should be passed. You can get the scale factor by using the function GMP::Column::GetScale.

  • Hint values and priorities are only supported by GUROBI.

Example

Assume we have a GMP for which we have two solutions in the solution repository at positions 1 and 2. Our goal is to add up the level values of each column in the solutions, and place the result in the solution at position 3 in the solution repository. This can be done in a generic way using the function GMP::Instance::GetColumnNumbers as follows. Here ColumnNrs is a subset of Integers with index c.

! Get the column numbers of all variables in myGMP.
ColumnNrs := GMP::Instance::GetColumnNumbers( myGMP, AllVariables );

for ( c ) do
    ! Get level value of column c in solution 1.
    val1 := GMP::Solution::GetColumnValue( myGMP, 1, c );
    ! Get level value of column c in solution 2.
    val2 := GMP::Solution::GetColumnValue( myGMP, 2, c );

    ! Assign the sum to column c in solution 3.
    GMP::Solution::SetColumnValue( myGMP, 3, c, val1 + val2 );
endfor;

! Send solution 3 to the (symbolic) model identifiers.
GMP::Solution::SendToModel( myGMP, 3 );

In the next example, we use the current level values of the variable JobSchedule as variable hints:

myGMP := GMP::Instance::Generate( FlowShopModel );

for (j,s) do
    GMP::Solution::SetColumnValue( myGMP, 1, JobSchedule(j,s),
                                   JobSchedule(j,s).level, 2 );
    GMP::Solution::SetColumnValue( myGMP, 1, JobSchedule(j,s), 10, 3 );
endfor;

GMP::Instance::Solve( myGMP );

In this example the hint priority for JobSchedule is set to 10.