[ojAlgo-user] Problem with mixed integer linear programming

[Julien.Cojan <Jul...@op...>]

Hello,

I am using OjAlgo to solve mixed linear programming problems.
However I often get a NullPointerException when running on my examples.
I tried version 30.0 and 30.6, I get the same error.

This is the smallest example I could find where I get this exception :


import static org.ojalgo.constant.BigMath.ONE;
import static org.ojalgo.constant.BigMath.ZERO;

import java.math.BigDecimal;

import org.ojalgo.optimisation.Expression;
import org.ojalgo.optimisation.Variable;
import org.ojalgo.optimisation.linear.LinearExpressionsModel;


public class TestOjAlgo {

	public static void testBug1(){
		Variable[] objective = new Variable[] {
				new Variable("X").weight(ONE),
				new Variable("Y").weight(ZERO),
				new Variable("Z").weight(ZERO)};

		objective[1].setInteger(true);

		LinearExpressionsModel model = new LinearExpressionsModel(objective);

		// c1: X =0
		Expression c1 = model.addEmptyLinearExpression("c1");
		c1.level(ZERO);
		c1.setLinearFactor(0, ONE);

		// c2: -X +5Y =0
		Expression c2 = model.addEmptyLinearExpression("c2");
		c2.level(ZERO);

		c2.setLinearFactor(0, new BigDecimal(-1));
		c2.setLinearFactor(1, ONE);

		// c3: X -Z =0
		Expression c3 = model.addEmptyLinearExpression("c3");
		c3.level(ZERO);
		// bugs with this constraint
		c3.setLinearFactor(0, ONE);
		c3.setLinearFactor(2, new BigDecimal(-1));
		// but not with this one ???
//		c3.setLinearFactor(0, new BigDecimal(-1));
//		c3.setLinearFactor(2, ONE);

		model.minimise();
	}

	public static void main(String[] args){
		testBug1();
	}

}





I get the following message
Exception in thread "main" java.lang.NullPointerException
	at org.ojalgo.optimisation.OptimisationSolver$Result.<init>(OptimisationSolver.java:99)
	at org.ojalgo.optimisation.integer.IntegerSolver.solve(IntegerSolver.java:318)
	at org.ojalgo.optimisation.ExpressionsBasedModel.solve(ExpressionsBasedModel.java:741)
	at org.ojalgo.optimisation.ExpressionsBasedModel.minimise(ExpressionsBasedModel.java:458)
	at TestOjAlgo.testBug1(TestOjAlgo.java:57)
	at TestOjAlgo.main(TestOjAlgo.java:61)


Is it a bug or am I not using ojAlgo properly ?


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