Troubleshooting
Always look for a more efficient model.
Bounds could be tightened; coefficients’ magnitude can be reduced
by rescaling of the data; you might not need certain constraints
or logical conditions when using a different approach.
Sometimes, just a different
formulation can help, for example, a logical condition
can be manually linearized.
See sections Efficiency considerations and Numerical accuracy.
Play with AMPL options
and Solver options.
Prominent ones are AMPL presolve
(switch off: ampl: option presolve 0;) and solver’s presolve
(ampl: option gurobi_options 'presolve=0';) and others
(tolerances, numfocus, intfocus, etc.)
To see what MP and/or the solver do with your model, export
the solver’s received model, and, if possible, the solver’s presolved model:
option gurobi_options 'writeprob=disj.lp writepresolved=disj_pre.lp';
option gurobi_auxfiles rc; ## To use var/con names
solve;
MP offers ways to explore automatic reformulations.
If you decide to contact AMPL or solver support, please provide a (possibly reduced)
version of your model reproducing the issue. Please also provide
the AMPL solver version by running highs -v
or solver logs obtained with options version outlev=1.
If you cannot reduce the model and don’t
want to show it, give us just the NL file produced by
option auxfiles ''; write bdisj;
For solver support, use MPS or another full-precision model format.