ampl/gurobi: can't open /tmp/at16918.sol

[Hend Ben Saad]

Hello everybody,

I am using a 32GB of RAM,  8 cores 64-bit Linux computer. When I run the problem with a small data set using (ampl/gurobi) everything works fine and gurobi gives me an optimal solution. But when I increase the problem size I get:

ampl: commands ilp.run;

Presolve eliminates 556000 constraints.
Adjusted problem:
556611 variables, all binary
806111 constraints, all linear; 556055500 nonzeros
    1111 equality constraints
    805000 inequality constraints
1 linear objective; 556611 nonzeros.

Error at _cmdno 1117410 executing "solve" command
(file ilp.run, line 36, offset 828):
can't open /tmp/at16918.sol

Through top command I see that only ampl is running and gurobi not invoked yet.. ampl consumes up to 98% of RAM. I wonder if the issue occurs when ampl is trying to pass the problem to gurobi and it is running out of memory !? because I thought 32 GB is largely enough RAM ...

Any suggestions on how to fix this ?

Thanks,

[Robert Fourer]

To troubleshoot this problem and see whether memory might be insufficient, add the command

option times 1, gentimes 1;

before "solve;". This will produce a lot of diagnostic output as described at http://ampl.com/faqs/what-should-i-do-if-i-suspect-that-there-is-insufficient-memory-for-my-ampl-session/. You can post that here to get more advice.

Bob Fourer
am...@googlegroups.com

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[Hend Ben Saad]

Thank you very much, the explanation in the link you referred is very useful.