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I am trying to solve a PILP model in Lingo.

There are total of 138 integer variables, 211 integer constraints in the model. I have a maximization objective. However, this model is taking a very long time (Its already 9hours 5minutes since I gave the solve command on Lingo.

The "best objective" also has not shown any improvement from the past few hours.

I wish to know the possible reason for not being able to reach the global optimal solution. Is it a natural phenomenon to take such long time or should I need to check something?

Ankita Panchariya
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  • The problem is in general NP-hard -> so the general answer: yes it's natural. Not much can be added with such sparse information. – sascha Nov 27 '19 at 17:01
  • Try a different MIP solver, e.g. through [NEOS](https://neos-server.org/neos/). (Use export as MPS file). A few hundred integer variables is usually not very difficult. I don't understand the difference between an integer variable and an integer constraint. – Erwin Kalvelagen Nov 27 '19 at 19:00

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