i write the supply chain model in LINGO. my model is MILP and My objective function is maximize profit, but when i solve the model, some variables(like: quantity of product p shipped to market t in time period t) give zero values, just one variable take value from 171 variables...i don't know whats the problem, can anyone help me?
That seems to be a logical result. If your model doesn't include minimal demands, maximal amounts which could be sold, or intedependences between the products just the most profitable product will be produced/shipped.
I think that Ralf is right, because apparently the solutions polytope is not formed, but also it could be because there is only one variable that satisfies all restrictions
Dear Adam
Agree. It is most probable, and that coincides with what Ralf suggested
Remove from the model the one (and only) variable which takes non-zero value, and see what are the values of the 170 variables that are otherwise zeros. If they are still zeros then perhaps there is something wrong with the model.
Another idea could be to set some variables to be non-zero and check if some constraints are violated, and, if so, how much. Perhaps some constraints are incorrect in the sense they are too tight, not too loose...
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