Topics started by Jean
Hello everyone, CPLEX returns optimal solution for small instances of a MIP model. But when try to solve a larger instance, CPLEX return a local optimum (solution checked by a heuristic). The model is MIP with a number of Big-M formulations that are replaced by Indicator Constraints. For one of the large instances: # of constraints: 2086337 #of variables: 1122331 (66225 int) #of none zero: 7223176 It takes 53557 seconds for CPLEX to close the optimality Gap. Any idea? please share your thought.
I am trying to solve an MIP model with AIMMS. I run the AIMMS for a specific parameters and obtained the optimal solution; I also solved the model with same data/parameters using a heuristic to test the optimal solution- it is indeed the optimal. Now I first change the parameters (i.e., using different values) and save the changes in a new "case" using "save case as" option under different name. Then I set the new case as the "active case" and try the model with the new data. surprisingly AIMMS returns the (same) optimal solution obtained with original "case". I used to use the "single file data management" so I thought this might be the reason. I changed this to "disk files and folders" by going to Menu File > Open > Data file>convert...but it didn't help at all. I also noticed that when I load a case, the model's decision variables contains some values from perhaps previous runs; not sure if this is normal with AIMMS. Any help on this is greatly appreciated in advance. Thank
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