Re: [ojAlgo-user] Problem with mixed integer linear programming

[Anders P. <an...@op...>]

I uploaded a new snapshot 

https://sourceforge.net/projects/ojalgo/files/ojAlgo/snapshot/

Could you test if that works better for you?

/Anders


On 10 okt 2011, at 14:45, Anders Peterson wrote:

> Haven't looked at this in great detail, but if you change:
> 
> 	objective[1].setInteger(true);
> to
> 	objective[1].setInteger(false);
> 
> and
> 
> 	model.minimise();
> to
>        model.setMinimisation(true);
>        final OptimisationSolver tmpSolver = model.getDefaultSolver();
>        final Result tmpResult = tmpSolver.solve();
> 
> Then you'll see that ojAlgo reports the relaxed problem to be unbounded. If that's true it's a (big) problem for the integer solver. The relaxed problems need to be able to be solved by the linear or quadratic solvers.
> 
> I'm not confident that ojAlgo reports INFEASIBLE and/or UNBOUNDED problems right all the time, but you should definitely not get a NullPointerException!
> 
> X=0, Y=0 & Z=0 is a valid solution to your problem, right? In that case there is a bug with the LinearSolver.
> 
> /Anders
> 
> 
> On 10 okt 2011, at 12:18, Julien.Cojan wrote:
> 
>> 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 ?
>> 
>> 
>> -- 
>> The Open University is incorporated by Royal Charter (RC 000391), an exempt charity in England & Wales and a charity registered in Scotland (SC 038302).
>> 
>> 
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> 
> 
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> definitive record of customers, application performance, security
> threats, fraudulent activity and more. Splunk takes this data and makes
> sense of it. Business sense. IT sense. Common sense.
> http://p.sf.net/sfu/splunk-d2dcopy1
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> ojAlgo-user mailing list
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> https://lists.sourceforge.net/lists/listinfo/ojalgo-user
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