Frequently Asked Questions

General

Which solvers should I get?

The choice of the solvers will depend on your requirements and is problem specific - each solver can handle certain model types as explained here.
Also, take a look at our price list.

We cannot generally recommend a certain solver, but we are happy to provide you an evaluation license so you can try out yourself which solver will be best for your purposes.
Especially for NLP (and also GLOBAL) problems it might make sense to get more than one solver, since they use different algorithms. For this reason we offer package discounts for NLP and GLOBAL solvers.

Which solvers are included with the BASE Module?

GAMS/BASE includes the Open Source (COIN-OR) solvers: Bonmin (MINLP), Cbc (LP, MIP), Couenne (MINLP), Ipopt (NLP) and for academic licenses also SCIP and Soplex. Also NLPEC (MCP, MLPEC), BDMLP (LP, MIP), MILES (MCP) and LS.
A full list of what is included with the GAMS/BASE Module

What are Solver-Links? What is the differences between a GAMS/Solver and the GAMS/Solver-Link?

A GAMS/Solver-Link connects the GAMS Base Module to a Solver but does not contain a license for the solver. If you would like to purchase the Solver-Link, we require your confirmation that you have a standalone license for the current version of that solver and that your use will comply with the respective license agreement. Some of our solver vendors offer academic programs that may be able to provide you with a free license for their respective solver libraries.

Licensing

What does maintenance mean?

A GAMS license is perpetual and includes one year of maintenance and support after the purchase of the software. Being up-to-date with maintenance allows the user to work with the latest distribution of our software. Maintenance also enables the option to make changes to the license like adding components or users, switching the platform, or getting a multi-copy discount for additional licenses. If the user does not purchase maintenance for some period and chooses to purchase it at a later date, we will charge the prevailing annual maintenance and support fees for the periods that were not covered.

What do you count as a user?

GAMS licenses are based on the number of named GAMS users within an organizational unit. To determine the number of users, we count the total number of people that will use GAMS as part of their job or research, not similtaneous or concurrent uses. A GAMS user is welcome to install GAMS on more than one computer - assuming that only one of those computers will be used at a time. Single user licenses are restricted to a particular individual (the licensee mentioned in the license file).

What types of licenses do you offer?

Our standard licenses are based on the number of named GAMS users within an organizational unit. (see above "What do you count as a user?" for more details on this)

If a user-based licensing cannot be applied, we also offer machine based licenses. A single machine license can be installed on one machine with no restriction on the number of users. Please contact us for more information on this.

Can I get a discount?

All prices are according to our published price list. We have the policy of treating all our customers equally and thus do not provide random discounts.

Technical

What hardware is recommended for running GAMS?

We have prepared an overview of hardware recommendations in our support wiki.

How can I change the default solver in GAMS?

Changing the default solver can be done in various ways:

  1. Windows: Using the GAMSIDE: File → Options → Solvers. Click on the intersection of solver and model type that you want to be the default combination.
  2. Unix: Run gamsinst again and change the default solver there.
  3. Use a command line parameter, e.g. nlp=CONOPT
  4. Add a line to your model (before the current solve statement) to switch your solver: option nlp=conopt. This will override all other settings and will tell GAMS to use GAMS/CONOPT to solve NLP models instead of the default NLP solver.

Note: Solvers, which call other solvers as a sub system (i.e DICOPT or SBB) may require an option file to change the default solver for the sub problem. Please refer to the solver documentation for more information.