Search found 340 matches

by bussieck
2 years ago
Forum: Solvers
Topic: Multiobjective optimization
Replies: 1
Views: 1565

Re: Multiobjective optimization

Your analysis is correct. For other readers, this is only for the GAMS/Gurobi solver. Anyhow, in case of "MultiObj=1" the coefficients in the master objective "just" help to build the different priority classes. When I implemented this, I had in mind that I wanted to go easily from a pure weighted t...
by bussieck
2 years ago
Forum: Solvers
Topic: Problems with the initial point
Replies: 4
Views: 1582

Re: Problems with the initial point

Tiago, I agree that we should make sys12 more visible and give it a better name, but I also believe that this is a good default. Even global solvers benefit from a good starting point because they use local solvers for local search (e.g. BARON does a multi-start based on the initial point that hopef...
by bussieck
2 years ago
Forum: Solvers
Topic: CPLEX LP Warmstart
Replies: 3
Views: 1744

Re: CPLEX LP Warmstart

It does not matter where the basis (complete or incomplete) comes from. You just need to set (.l and) .m of your variables and equations. I did not get the experiment you tried to do in your attached GAMS model. To me it looks like that the second solve successfully restarted from a basis.

-Michael
by bussieck
2 years ago
Forum: Solvers
Topic: CPLEX stuck "Removing shift" on MILP
Replies: 3
Views: 1206

Re: CPLEX stuck "Removing shift" on MILP

This truly looks like a Cplex bug or numerical issue. If you add options writesav prob.sav writeparam param.prm to your GAMS/Cplex option file you could submit these two files together with the entire log to support@gams.com or directly to the Cplex folks. Please also provide information about the p...
by bussieck
2 years ago
Forum: Solvers
Topic: Problems with the initial point
Replies: 4
Views: 1582

Re: Problems with the initial point

Local NLP solvers need a good starting point to improve on. The starting point you provide (0,0) can't be evaluated and hence the solver could not compute a direction that improves the situation. Hence GAMS checks if the starting point can be calculated. If not, GAMS will not pass the model to the s...
by bussieck
2 years ago
Forum: Bugs
Topic: Gams does not print solution when click "Interrupt" on windows 10
Replies: 1
Views: 1714

Re: Gams does not print solution when click "Interrupt" on windows 10

The problem is that GAMS waits for the user to react on the "Terminate batch job (Y/N)?". With older OS versions this was not a problem but it surfaced eventually. Anyhow, a newer GAMS version (>=24.0) fixes this problem (see http://www.gams.com/latest/docs/releasenotes/24.0.html#gams). You can work...
by bussieck
2 years ago
Forum: Solvers
Topic: CPLEX LP Warmstart
Replies: 3
Views: 1744

Re: CPLEX LP Warmstart

Leo,

The key GAMS/Cplex option for LP restarts is 'advind' (http://www.gams.com/latest/docs/solvers ... PLEXadvind). Perhaps you can post some logs or even share your model and starting point, so we have more to go on.

-Michael
by bussieck
2 years ago
Forum: Tools
Topic: Saving solution with partial solve, and restarting solve
Replies: 2
Views: 1339

Re: Saving solution with partial solve, and restarting solve

Restarting an LP solver from a previous basis used to be easy and reliable 20 years ago. We even had some tests that for this. With modern LP solvers this is not necessarily the case anymore, let along MIP solvers. Very often you have to decide to a) start from an advanced basis and not do presolve ...
by bussieck
2 years ago
Forum: Solvers
Topic: BONMIN branch and bound
Replies: 2
Views: 1283

Re: BONMIN branch and bound

Not sure how many people understand the BONMIN log. My colleague Stefan Vigerske who implemented the GAMS/BONMIN link says he doesn't understand the log either (he suspects that these NLPs are related to some primal heuristics). I guess you need to go to the computer (https://projects.coin-or.org/Bo...
by bussieck
2 years ago
Forum: Solvers
Topic: how to reduce memory use of cplex
Replies: 3
Views: 1976

Re: how to reduce memory use of cplex

Hi, The documentation has a few hints: http://support.gams.com/solver:error_1001_out_of_memory But I fear that most of these really won't make much of a difference if the tree gets that large (13GB!) . The options that will make a difference (e.g. nodsel/varsel) will most likely compromise the perfo...