Decision Optimization

Decision Optimization

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  • 1.  ILOG Concert representing optimization expression as code

    Posted 02/17/11 02:08 AM

    Originally posted by: SaqibIlyas


    Hi everyone
    I have an optimization problem in which I am unable to represent the cost function as a matrix expression of some sort. But, given a feasible solution, I can compute the cost using C code. Is there a way to pass the cost function expression to ILOG through concert, such that it invokes my code to compute the cost? Any samples?
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  • 2.  Re: ILOG Concert representing optimization expression as code

    Posted 02/17/11 10:13 AM

    Originally posted by: SystemAdmin


    Is your objective function linear?

    Paul

    Mathematicians are like Frenchmen: whenever you say something to them, they translate it into their own language, and at once it is something entirely different. (Goethe)
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  • 3.  Re: ILOG Concert representing optimization expression as code

    Posted 02/17/11 10:46 AM

    Originally posted by: SaqibIlyas


    No, it's not.
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  • 4.  Re: ILOG Concert representing optimization expression as code

    Posted 02/17/11 05:44 PM

    Originally posted by: SystemAdmin


    CPLEX handles only linear and convex quadratic objectives, so if your objective is quadratic (and convex for a minimization/concave for a maximization), you'll need to find a different software package.

    If your objective is quadratic and meets the convexity condition, you could try a cutting plane approach. Create a variable z and maximize or minimize it, whichever is appropriate, subject to your constraints (which will initially not contain z). You'll need to bound z above (maximizing) or below (minimizing). As each "solution" is encountered, you'll need to generate not just the objective value but a supporting hyperplane of the objective function and add that as a constraint. That may require numerical differentiation on your part.

    Back in the vacuum tube era, I seem to remember cutting plane methods having a reputation for slow convergence. My guess is that, even with a suitable quadratic objective, you might be better served by a nonlinear optimization program.

    Paul

    Mathematicians are like Frenchmen: whenever you say something to them, they translate it into their own language, and at once it is something entirely different. (Goethe)
    #DecisionOptimization
    #MathematicalProgramming-General


  • 5.  Re: ILOG Concert representing optimization expression as code

    Posted 02/18/11 11:52 AM

    Originally posted by: SaqibIlyas


    Thanks, Paul. In a scenario such as mine, where representation of the cost function using matrix algebra does not seem to be possible, is there a suitable nonlinear optimization tool available? I have tried Matlab's fmincon. I've coded the problem in Matlab using matrix operations except for the cost function which could only be implemented using loops and other constructs. Matlab seems to be very efficient when working with matrices but when I throw in the loops into the cost function, even though I coded the cost function in C and interfaced it using MEX, it is really really slow for a reasonable-sized problem.
    Perhaps a tool that runs natively in C/C++ might be faster and if it allows me to express the cost function as code, it might work for me. And I'm not even talking of mixed integer programming here.Any suggestions?
    Thanks and best regards
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  • 6.  Re: ILOG Concert representing optimization expression as code

    Posted 02/18/11 10:23 PM

    Originally posted by: SystemAdmin


    Sorry, I don't have any personal experience with nonlinear solvers. There are several nonlinear optimization projects at COIN-OR; you could perhaps ask on their mailing list, or on OR-Exchange.

    Paul

    Mathematicians are like Frenchmen: whenever you say something to them, they translate it into their own language, and at once it is something entirely different. (Goethe)
    #DecisionOptimization
    #MathematicalProgramming-General


  • 7.  Re: ILOG Concert representing optimization expression as code

    Posted 03/09/11 02:06 AM

    Originally posted by: SaqibIlyas


    Thanks Paul
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    #MathematicalProgramming-General