Question

Warning: Model is not yet optimal

  • 16 June 2020
  • 1 reply
  • 211 views

Hello,

I have implemented the simple nonlinear problem in AIMMS which uses the CONOPT 4.0 solver to solve it. But whenever I run the code, the objective function value changes and I get the warnings like:   "Warning: After 252 iterations CONOPT 4.0 terminated and BasicStateEstimation is not yet optimal. The minimum found for obj is 704.122936573."   It seems that the optimization procedure stops before convergence. Therefore, I checked the "stop criteria" from the "solver general" and "specific solver" icons and changed some of them, but I still have the same issue. Would you please tell me how I can solve this issue? Please let me know if you need the code.   Regards

1 reply

Userlevel 3

Hi @HosseinMehdipour. CONOPT is a local nonlinear solver and therefore there is no guarantee that it will find a global optimal solution (unless the model is convex). If you resolve the model, without closing and opening the project in between, then CONOPT will use the solution of the previous solve as a starting point, which can have an influence on the (local) optimal solution that it finds.

You might get better solutions if you use the multi-start algorithm in AIMMS. See the AIMMS Language Reference for more information, and the circle packing example for an example that uses the multi-start algorithm.

Changing the model formulation could also help but for that I would need the see the AIMMS project. If you want me to review your model then please attach your project here, after adding it to a zip file, or send it to our support by email if your project contains sensitive information.

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