Let's put it simple. Having the following linear programming (LP) problem,
our goal is to generate, in the most simple and intuitive way, a fixed-format MPS file representing the problem.
We import the fixed-mps
library from Maven with
<!-- https://mvnrepository.com/artifact/eu.irzinfante/fixed-mps -->
<dependency>
<groupId>eu.irzinfante</groupId>
<artifactId>fixed-mps</artifactId>
<version>1.1.1</version>
</dependency>
Now, the instruction for building the LP problem is the following:
import eu.irzinfante.fixedmps.core.Problem;
import eu.irzinfante.fixedmps.core.Problem.ProblemBuilder;
import eu.irzinfante.fixedmps.core.Variable.VarBuilder;
import eu.irzinfante.fixedmps.core.Constraint.ConstraintBuilder;
Problem lp = new ProblemBuilder(
new VarBuilder(-1).lowerBound(0).upperBound(Double.MAX_VALUE).integer().build(),
new VarBuilder(-1).lowerBound(0).upperBound(Double.MAX_VALUE).integer().build()
)
.addConstraint(new ConstraintBuilder(-2, 2).greaterThan(1))
.addConstraint(new ConstraintBuilder(-8, 10).lessThan(13))
.build();
As we can see, the coefficient for each variable in the objective function is given at the time of declaring the variable. We tell also at this point if the variable is integer or binary (or we just build the variable to tell that it is a real).
Then we add the constraints for the problem row by row, giving the coeffient for each variable in order, an telling the type of the constraint (,
or
) and the value of the free term.
Now, to get the MPS file (as a String) from the problem we do this:
import eu.irzinfante.fixedmps.util.MPSUtil;
MPSUtil.obtainMPSfile(lp)
The result in this case would be:
NAME FIXEDMPS
ROWS
N OBJ
G C0000001
L C0000002
COLUMNS
INT1 'MARKER' 'INTORG'
X0000001 C0000002 -8.00000e+00 C0000001 -2.00000e+00
X0000001 OBJ -1.00000e+00
X0000002 C0000002 +1.00000e+01 C0000001 +2.00000e+00
X0000002 OBJ -1.00000e+00
INT1END 'MARKER' 'INTEND'
RHS
RHS1 C0000001 +1.00000e+00
RHS1 C0000002 +1.30000e+01
BOUNDS
UP BND1 X0000001 +1.00000e+10
UP BND1 X0000002 +1.00000e+10
ENDATA
Copyright (C) 2020-2023 Iker Ruiz de Infante Gonzalez iker@irzinfante.eu
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