Convert presolved model to original model

Answered

Christian Perau

• November 19, 2024 12:48

I am working with rather big models. After the presolve (during the ordering) I notice the highest peak in memory usage. Due to this peak I often have to reduce the Threads parameter and therefore increasing the computation time during the solving (I use Method=2 and Crossover=0 by the way).

After the ordering I often end up with ~30% of memory usage (peak at 99%). I was wondering if there is a way to do the presolve and ordering in a first step (with reduced Threads), increase the Threads and finally solve the model with the increased number of Threads? This way I could use my resources more efficiently. I am working with Gurobi 11.0.3 in C. 

I could just solve the presolved model but as far as I see the output the ordering happens  only before running GRBoptimize, right?

Related to

• Presolve

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  Matthias Miltenberger

  Gurobi Staff

  • November 19, 2024 13:45

  Hi Christian,

  I am afraid there is no easy way of "maximizing your thread usage". There are simply some parts of the solving process that can be parallelized better than others, and there are some parts that require more memory than others.

  There is no way of dynamically changing the number of threads during a run. This would introduce a high amount of complexity and likely also non-determinism to the solver.

  Cheers,
  Matthias

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