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File Format
Extension(s) .gms, .opt*, .gdx, .inc, .lst, .lxi, .efi, .ref
Released 1978

GAMS is a programming language and software suite to model mathematical optimization problems. It enables a wide variety of models to be described with many thousands of variables. Running a GAMS problem solves the models described in the source code, but can also do other things. The language is proprietary. A number of file types and extensions are used by GAMS:



The main source code for a GAMS project is in one or more text files ending with .gms extensions. This defines variables, equations, and other important parts of the model definition.


These are options files for specific solvers in GAMS. They may have secondary extensions after the .opt to distinguish them, as their file name determines which solver they affect. For example, a CPLEX options file may be named CPLEX.opt, or to distinguish it from other options files for that solver. According to GAMS, these may also end in .op* or .o*.


GDX files are binary data files. These can be read and edited with GAMS, or with other programming languages using libraries that are included as part of GAMS.


"Include files." I have no idea what these are, but they're apparently text files.

.lst, .lxi, .ref

These are text files created by GAMS. .lst files show logs and results from the solving process. .lxi files are a sort of intermediate language. .ref files are used for debugging. LST files are also called "MASM Listing" files, however, they should not be confused with Microsoft Assembler files (also called MASM).


Short for "External files", these are text files which denote which files need to be sent when using cloud computing.

Other files

GAMS also may use a YAML file called gamsconfig.yaml, and supposedly also .ref "reference" files, but I don't know anything about that one.

References and more information

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