Gurobi Stuck After Solving Problem

Ongoing

Konstantin Preußer

• January 03, 2023 07:16

I solve a large MILP with Gurobi. It takes about 12 hours to finish. When it finds the optimal solution the algorithm prints "Solved with primal simplex". Afterward, nothing happens. I let it run for multiple hours after that but nothing changes. It seems to be stuck in another method or so that verbose does not print.

The log looks like this at the end.

Waiting for other threads to finish...       39807s
Concurrent spin time: 4957.69s (can be avoided by choosing Method=3)

Solved with primal simplex

Any ideas as to why this happens?

Related to

• Simplex
• Concurrent

1

• 

  Silke Horn

  Gurobi Staff

  • January 03, 2023 08:27

  Gurobi uses the concurrent optimizer to solve your LP, i.e., it runs multiple algorithms in parallel; the fastest one wins the race. However, to keep the behavior deterministic, it needs to continue with the losing threads for a little (or, as in your case, long) while longer.

  You can try avoiding this by using another method: You could set Method=0 to run only primal simplex or Method=3 for non-deterministic concurrent.

  Best regards,
  Silke

  1
• 

  Miran Kavrečič

  • December 04, 2023 14:23

  

  Hi,

  is Method set as a environment or as a model parameter? I've to set the Method parameter to both

  grbEnv.Method = 3;
  grbMod.Set(GRB.IntParam.Method, 3);

  but the solver still "hangs" on "Waiting for other threads to finish...". Setting the parameter to 0 prevented "waiting for other threads" but increased the computational time until the point when the message starts appearing.

  Any additional ideas?
  Thanks

  0

Please sign in to leave a comment.