Decision Optimization

Decision Optimization

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  • 1.  inequality

    Posted 05/20/09 07:16 PM

    Originally posted by: SystemAdmin


    [morteza4321 said:]

    Hello

    Dose any one know how we can enter inequality constraints in CPLEX (for example x[i]-x[j] 0) ?
    Is there any other solution rather than using Abs?

    Best

    #DecisionOptimization
    #MathematicalProgramming-General


  • 2.  Re: inequality

    Posted 05/20/09 09:00 PM

    Originally posted by: SystemAdmin


    [prubin said:]

    I don't think you can, since for one thing it results in an improperly posed optimization model.  You want a convex feasible region (or, for discrete problems, a continuous relaxation with a convex feasible region), and A B does not result in one.  For a continuous problem, you need something like
      A - B >= z*epsilon - (1-z)*M
    and
      B - A >= (1-z)*epsilon - z*M

    where z is a 0-1 variable, M is a sufficiently large positive parameter (an a priori bound on |A-B|), and epsilon is a small but strictly positive parameter.  If A and B are integers, then epsilon = 1.

    /Paul
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