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Solver is not solving

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  1. #1
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    Solver is not solving

    Hello,

    I have a problem concerning below task.

    Task description: Factory produces three products, but only two products can be produced in a one day. Production capacity is 2100 ea per day. The ratio of one product’s daily production quantity to another must be 1:2, 1:1 or 2:1. Weekly raw material availability is limited and shown in the table. It’s necessary to make production plan maximizing production capacity usage.

    I decided to solve the task by Solver. I've made the model as in the attached file, but it doesn't do anything.

    Please help, whether my model is not correct or there is another way (not Solver) of solving!

    Thank You!
    Attached Files Attached Files

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    Re: Solver is not solving

    I think those kind of problems should be solved with Evolutionary algorithm. Also, under options unhook the box that says ignore integer contstraints.

    I did some changes to the layout and your formulas, I have no clue if that makes a difference.

    With the sheet setup as it should, Solver runs but it cannot find a solution within the constraints if you start with all zeroes.
    What I did was loosen up the constraints a bit ( 2 OR 1 products a day instead of just 2) and then I reduced the number of options (maximum 3 instead of 4). Solver then found a solution within the constraints. Starting from that solution I increased maximum back to 4 and started and it found a pretty good solution. Oh yeah, I also increased the number of iterations by a factor of 10, I have no idea what that even means, I'm only guessing.
    Note that I put all equal looking days next to each other to make it look good.

    Before I could make Solver cooperate I considered writing a post saying this would be faster to do manually. That might still be true but it's more fun trying to manipulate Solver than trying to manipulate the numbers.
    Attached Files Attached Files
    Last edited by Jacc; 02-16-2014 at 01:14 PM.
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    Re: Solver is not solving

    Just a small manual adjustment on the previous result. I think this is as good as it gets.

    Optimal.JPG

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    Re: Solver is not solving

    Dear Jacc, thanks for your response!!

    Initially I forgot to mention that I’ve found the best result and placed it on the second sheet of my attachment. Can you imagine, my way was very similar to yours. But unfortunately it’s not that I need. I do really need the method which strictly gives ideal solution by the first trial. I mean the result is the secondary importance (after all it can be found manually as you wrote), but the first importance is faultless method. Probably Solver is not it, and I do not know any others. Your ingenious ideas would be highly appreciated!

    Thank you!

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    Re: Solver is not solving

    I don't think a "always fast and correct" solution to this problem exists. It's like the travelling salesman problem or similar. http://en.wikipedia.org/wiki/Travell...lesman_problem
    http://en.wikipedia.org/wiki/Cutting_stock_problem

    There are numerous problems like this, scheduling problems, cut-length-to-minimize-waste problem (pipe or board or whatever).

    Maybe it is possible to write a algorithm that is better than Solver if it's made for just this problem but I don't think it will be correct every time either.

    If the problem is small enough I guess it would be possible to loop through all combinations possible but I am not up to writing that algorithm. Also I think you would have to leave your computer running for a long time.

    Edit: Solver themselves confirm that the evolutionary solver is reasonably good at finding "a solution" but not finding the best solution. http://www.solver.com/content/basic-...ing-conditions
    Last edited by Jacc; 02-17-2014 at 10:39 AM.

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    Re: Solver is not solving

    Thank you, Jacc!
    You are the one who ever can discourse on this topic so far-sightedly

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    Re: Solver is not solving

    well i tried it again but this time i picked 10 values from the 24 and summed them so i knew there was a definite answer
    so i set solver to find the sum of those 10 which i know exists and it still failed miserably. i even tried rounding everything as -ve numbers often cannot be stored correctly still no joy
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    Re: Solver is not solving

    Thank you, Martin...
    It seems "always fast and correct" solution to this problem doesn't exist...

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