From: maywood on 4 Jan 2010 05:22 Hi and a happy new year! I still got problems with an production optimization. In the attached excel file you will find demand data, maximum and minimum stocks, production capacity and stocks for 13 months I need to satisfy demand each month by the use of stocks, new production or purchase. The use of stocks is the cheapest alternative and purchase the most expensive alternative. The sum of provided quantities times costs should be minimzed. My problem is the following: The production should happen in batches of at least 500 pieces (if capacity is sufficient) or should be zero if stocks are sufficient to meet demand. This is why I introduced a binary variable which is linked with production quantities. When I solve the optimization problem with the Excel Solver, the binary variable and the production quantities in each month are zero but the more expensive purchase is always positive. Does somebody know why? Are there constraints wrong or missing? http://www.herber.de/bbs/user/66969.xls From: Bernard Liengme on 4 Jan 2010 10:26 Solver problems are of interest to me but I do not completely understand your worksheet Let's start by doing the problem for just one month Please correspond with me directly - get my email address from my website -- Bernard Liengme Microsoft Excel MVP http://people.stfx.ca/bliengme "maywood" wrote in message news:8A1A79C0-3215-40E0-BDEA-FFA003D5F6D4(a)microsoft.com...> Hi and a happy new year! > > I still got problems with an production optimization. In the attached > excel > file you will find demand data, maximum and minimum stocks, production > capacity and stocks for 13 months > I need to satisfy demand each month by the use of stocks, new production > or > purchase. The use of stocks is the cheapest alternative and purchase the > most > expensive alternative. The sum of provided quantities times costs should > be > minimzed. > My problem is the following: > The production should happen in batches of at least 500 pieces (if > capacity > is sufficient) or should be zero if stocks are sufficient to meet demand. > This is why I introduced a binary variable which is linked with production > quantities. > When I solve the optimization problem with the Excel Solver, the binary > variable and the production quantities in each month are zero but the more > expensive purchase is always positive. > Does somebody know why? Are there constraints wrong or missing? > > http://www.herber.de/bbs/user/66969.xls >