Using the General Algebraic Modeling System#

The General Algebraic Modeling System (GAMS) is a commercial high-level modeling system for mathematical programming and optimization. It is licensed software.

GAMS includes a DSL compiler and also a stable of integrated high-performance solvers. GAMS is able to solve complex, large-scale modeling problems. For documentation, forums, and FAQs, see the GAMS website.

A 60-user license of GAMS is made available to NREL users. This GAMS license requires users to be a member of the "gams workgroup." If you need the GAMS software package or a specific solver from GAMS, or if you have trouble running GAMS, please contact us.

Initializing Your Environment#

To initialize your environment to use GAMS, simply type module load gams/<version> — see module avail gams output to see available versions. GAMS is run with the command format gams <input filename>. A file <input filename>.lst will be created as the output file.

For a test run, in your home directory, type the following:

module load gams/<version>
cp /nopt/nrel/apps/gams/example/trnsport.gms .
gams trnsport

A result of 153.675 should be found from screen output. More detailed output is in the file trnsport.lst.

Selecting an Alternative Solver#

The available solvers for different procedures are shown in the following with the default solver being the first one:

LP: GUROBI BDMLP CBC IPOPT SOPLEX
MIP: GUROBI BDMP CBC SCIP
RMIP: GUROBI BDMLP CBC IPOPT SOPLEX
NLP: SCIP COUENNE IPOPT
MCP: NLPEC MILES
MPEC: NLPEC
RMPEC: NLPEC
CNS: SCIP COUENNE IPOPT
DNLP: SCIP COUENNE IPOPT
RMINLP: SCIP COUENNE IPOPT
MINLP: SCIP BONMIN COUENNE
QCP: GUROBI COUENNE IPOPT SCIP
MIQCP: GUROBI BONMIN COUENNE SCIP
RMIQCP: GUROBI COUENNE IPOPT SCIP
EMP: JAMS LOGMIP SELKIE

By typing gams <input_filename> on the command line, the default procedure LP and the default solver Gurobi will be used. In order to override the default option to use, e.g., Soplex, you can try the following two methods:

Use the option statement in your GAMS input file. For example, if your model input uses LP procedure and you want to use Gurobi solver to solve it, just add option lp=soplex to your input file.
Specify the solver in the command line, e.g., gams <input_filename> lp=soplex.

A sample script for batch submission is provided here:

Sample Submission Script

#!/bin/bash --login
#SBATCH --name gams_run
#SBATCH --nodes=1
#SBATCH --ntasks-per-node=36
#SBATCH --time=00:05:00
#SBATCH --account=<allocation-id>
#SBATCH --error=gams-%j.err
#SBATCH --output=gams-%j.out

# Ensure script location
cd $SLURM_SUBMIT_DIR

# Create runtime environment
module purge
module load gams/<version>

# Run GAMS
gams trnsport lp=gurobi

For a certain solver, necessary control parameters for the algorithm—such as convergence criteria—can be loaded from the option file named as <solver_name>.opt in the directory that you run GAMS. For example, for the Gurobi solver, its option file would be "gurobi.opt". For the details of how to set those parameters, please see the GAMS Solver Manuals.

Important Tip#

When using the Gurobi solver in GAMS, the user should NOT try to load the Gurobi module. Simply using "module load gams" will automatically load the Gurobi solver.

Using GAMS Python API#

For GAMS version < 40.0#

In order to use GAMS python API, the environment parameter $PYTHONPATH should include these two directories:

$GAMS_PYTHON_API_FILES/gams $GAMS_PYTHON_API_FILES/api_[version-of-python]

where version-of-python = 27, 36, 37, or 38 for python version 2.7, 3.6, 3.7, or 3.8, respectively. The python version can be obtained by using command python --version.

For example, for python 3.7 and the bash shell, $PYTHONPATH can be set using the following script:

module purge
module load gams/31.1.0
if [ -z ${PYTHONPATH+x} ]
then
        export PYTHONPATH=$GAMS_PYTHON_API_FILES/api_37:$GAMS_PYTHON_API_FILES/gams
else
        export PYTHONPATH=$GAMS_PYTHON_API_FILES/api_37:$GAMS_PYTHON_API_FILES/gams:$PYTHONPATH
fi

For GAMS version > 40.0#

The GAMS API can be installed using Anaconda and Pip. Please follow the instruction on the GAMS website. Currently GAMS supports python version 3.7~3.11. In general, it can be installed using the following command:

pip install gams[your choice of sub-module] --find-links $GAMS_PYTHON_API_FILES