Re: [ojAlgo-user] bug report: ILP problem

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

One or two months ago there was another problem report regarding the IntegerSolver returning non-integer solutions. That took me a long time to find/fix. The main problem was actually with the LinearSolver, and I believe it's the same here.

I'm a little short on time these days. This wont be a quick fix. If you want to try to debug the problem here's a few pointers:

1) To log debug info call 
	tmpModel.options.debug(LinearSolver.class);
specifying which solver class/implementation you want to debug.

2) Experiment with different values on the various options in
	tmpModel.options
and 
	tmpModel.options.problem
in particular.

3) The method
	SimplexTableauSolver#findNextPivotRow()
is a very likely culprit.

4) The IntegerSolver is multithreaded. To get log statement from one subproblem at the time set a breakpoint at the very beginning of the
	IntegerSolver.BranchAndBoundNodeTask#compute()
method.


/Anders


On 8 apr 2013, at 18:02, Jeff Sherman <jef...@gm...> wrote:

> Anders,
> Please disregard the previous attachment and run this one.  Also, on one run i got these results:
> Obj val: 5250.000000000088
> Optimal: true
> All vars:
> x1 = 5.25E+3
> x2013 = 1244
> x2014 = 1269
> x2015 = 1308
> 
> 
> On Mon, Apr 8, 2013 at 11:52 AM, Jeff Sherman <jef...@gm...> wrote:
> Andres, 
> Thanks for your response.  The attached code  produces the following results:
> x1 = 0
> x2013 = 1245
> x2014 = 1269.9
> x2015 = 1306.1
> 
> Note that x2014 and x2015 are set as integral variables.
> 
> If in the calls to model.addExpression, i change the strings that are passed in, I can also obtain the following results:
> x1 = 2890.64039409
> x2013 = 1244
> x2014 = 1269.45812808
> x2015 = 1307.54187192
> 
> I did some looking into the code and I noticed in the ExpressionsBasedModel class you have:
> 
> private final HashMap<String, Expression> myExpressions = new HashMap<String, Expression>();
> 
> and at points, you get a collection of myExpression.values(), the order of which is not guaranteed.  I'm not sure if you care about this ordering but i thought id point it out in case. 
> 
> The correct results for the problem are:
> x1 = 4849.999999997941
> x2013 = 1245
> x2014 = 1269
> x2015 = 1307
> 
> Please let me know if I can provide any additional information or clarification.
> 
> Best,
> Jeff
> 
> 
> 
> On Mon, Apr 8, 2013 at 5:22 AM, Anders Peterson <an...@op...> wrote:
> ...and please experiment with different values on the various model/solver options - in particular tmpYourModel.options..problem
> 
> /Anders
> 
> 
> On 8 apr 2013, at 08:58, Anders Peterson <an...@op...> wrote:
> 
> > It's better you send me source code that I can execute and use as a test case. /Anders
> >
> > On 8 apr 2013, at 01:25, Jeff Sherman <jef...@gm...> wrote:
> >
> >> When I execute the following program:
> >> Minimize
> >> 1*x1
> >> Subject To
> >> 1*x2013 >= 0
> >> 1*x2014 >= 0
> >> 1*x1 >= 0
> >> -5000.0*x2014 + 5100.0*x2013 + -1.0*x1 <= 0
> >> -5000.0*x2014 + 5100.0*x2013 + 1.0*x1 >= 0
> >> 5000*x2013 + 5000*x2014 = 19105000
> >> Bounds
> >> Variables
> >> x2014 integer
> >> x2013 integer
> >> x1 continuous
> >>
> >> I get these results which are suboptimal:
> >> x1 = 5899.999999996906
> >> x2013 =  1891
> >> x2014 = 1930
> >>
> >> Or these results (which seem to occur at random):
> >> x1 = Infinity
> >> x2013 =  0
> >> x2014 = 0
> >>
> >> Using another solver, I obtain:
> >> x1 = 4200.000000000075
> >> x2013 = 1892
> >> x2014 = 1929
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> Reduce network management and security costs.Learn how to hire
> the most talented Cisco Certified professionals. Visit the
> Employer Resources Portal
> http://www.cisco.com/web/learning/employer_resources/index.html
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> <TestILP.java>------------------------------------------------------------------------------
> Minimize network downtime and maximize team effectiveness.
> Reduce network management and security costs.Learn how to hire 
> the most talented Cisco Certified professionals. Visit the 
> Employer Resources Portal
> http://www.cisco.com/web/learning/employer_resources/index.html_______________________________________________
> ojAlgo-user mailing list
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