Search found 72 matches

by GabrielYin
2 weeks ago
Forum: Syntax
Topic: How to save an optimization model and re-solve it later
Replies: 0
Views: 263

How to save an optimization model and re-solve it later

Hi GAMS experts, I'm curious if there is a way to save the GAMS-generated model into a file, and then I could re-solve the saved model in another process of GAMS. I'm using GAMS/CPLEX and it could allow me to save an LP file, but I don't know how to convert that LP file into a GAMS readable model fo...
by GabrielYin
1 month ago
Forum: Syntax
Topic: GAMS/CPLEX Model Creation Time
Replies: 3
Views: 858

Re: GAMS/CPLEX Model Creation Time

Hi Gabriel, If you are in a situation where the solve is quick, but everything else is slower... a good place to start is to turn on profile: option profile = 1; You might also want to turn off some of the printing to the LST: option limrow = 0; option limcol = 0; option solprint = off; You will se...
by GabrielYin
1 month ago
Forum: Modeling
Topic: Performance Difference between LP and MIP with fixed integer variables
Replies: 1
Views: 662

Performance Difference between LP and MIP with fixed integer variables

Hello GAMS experts! I have a general and probably stupid question. I'm using GAMS/CPLEX. I'm wondering if there is any performance difference between "modeling the problem as an LP with all integer variables fixed as known parameter inputs" and "modeling the problem as an MIP with int...
by GabrielYin
1 month ago
Forum: Syntax
Topic: GAMS/CPLEX Model Creation Time
Replies: 3
Views: 858

GAMS/CPLEX Model Creation Time

Hi Experts, I have one question regarding the syntax that could output the GAMS/CPLEX model creation time. I have a huge but relatively simple model (0.7 million constrs/vars) in which the CPLEX solver time was only 4 seconds, while the actual elapsed time was above 10 minutes. I'm not sure if there...
by GabrielYin
2 months ago
Forum: Modeling
Topic: Best practice for 2 modelers developing a GAMS model?
Replies: 3
Views: 15016

Re: Best practice for 2 modelers developing a GAMS model?

GAMS syntax is very light-weighted so I am curious why you would need two people working on the GAMS modeling. But back to your question, if you think Git is too much, try SVN, though the latter one is far outdated for modern software development, but could be efficient as long as your team only has...
by GabrielYin
2 months ago
Forum: Syntax
Topic: How to implement the recurrence equation in GAMS?
Replies: 1
Views: 1444

Re: How to implement the recurrence equation in GAMS?

Your way of modeling recurrence equation is OK. It's just a lot of syntax you missed out.

1. You need a semicolon to close the equation definition.
2. You need to define p0.

Best,
Gabriel
by GabrielYin
3 months ago
Forum: Modeling
Topic: Tuning CPLEX solver options for large-scale MIP problems
Replies: 4
Views: 12778

Re: Tuning CPLEX solver options for large-scale MIP problems

Hi, I'm not super familiar with how CPLEX works, but Im also using CPLEX to solve my large-scap MIP problem. It is taking several hours to run. How do you tune the solver options to be near-optimal? How do you determine that its near-optimal? Hello GAMS experts! I'm working on solving a sequence of...
by GabrielYin
4 months ago
Forum: Modeling
Topic: Tuning CPLEX solver options for large-scale MIP problems
Replies: 4
Views: 12778

Re: Tuning CPLEX solver options for large-scale MIP problems

When switching from one version to another, I always give "default" a try (you can copy the tolerance options, e.g. epgap etc) but no algorithmic option and see how the solver does. If that's no good, then I would go for the meta options (e.g. mipemphasis) and depending on some experiment...
by GabrielYin
4 months ago
Forum: Solvers
Topic: mipemphasis
Replies: 4
Views: 11434

Re: mipemphasis

There are hundreds of CPLEX options which you need to play around to find the best solver option for speedup. You can find them here https://www.gams.com/latest/docs/S_CPLEX.html . Some useful solver options you might be interested in using: varsel: variable selection strategy scaind: input paramete...
by GabrielYin
4 months ago
Forum: Solvers
Topic: I need help to fix these errors in my model
Replies: 1
Views: 8405

Re: I need help to fix these errors in my model

Hi, First, this should be related to your model, so probably Model section in this forum would be more appropriate. Second, in your model, you are summing j in an equation indexed by j, which technically eliminates the j index in your equation. You would need to revise your modeling. Best, Gabriel