GAMS-AMPL

The NEOS Server offers the GAMS/AMPL solver for the solution of optimization problems in GAMS format. This solver internally reformulates the provided GAMS model as an AMPL model and uses the Kestrel interface to the NEOS Server to submit the reformulated model to the indicated AMPL solver. The results from the AMPL solve are then provided back to the user in the normal GAMS format.

Currently, the following list of AMPL solvers, along with the types of models they can solve, can be used with this service.

AFORTMP - quadratic and linear programs with mixed integer variables
BLMVM - bound constrained optimization problems
BPMPD - linear programs
FILTER - nonlinear and linear programs
KNITRO - nonlinear and linear programs
LANCELOT - nonlinear and linear programs
LBFGSB - bound constrained optimization problems
LOQO - nonlinear and linear programs
MINLP - nonlinear and linear programs with mixed integer variables
MINOS - nonlinear and linear programs
MOSEK - convex nonlinear and linear programs
PATH - complementarity problems
PENNON - nonlinear and linear programs
SNOPT - nonlinear and linear programs
TRON - bound constrained optimization problems

The user is responsible for choosing an appropriate AMPL solver for their particular model type. For example, giving a nonlinear program to a solver only capable of processing linear programs will result in undefined behavior. Typically, an error message will be generated.

Using the NEOS Server for GAMS/AMPL

The user must submit a model in GAMS format to solve an optimization problem. For security purposes, the model submitted must adhere to the following conventions:

The model must be self contained, i.e. no $include or $batinclude
No execution of external programs is allowed, i.e. no $call or execute
No file creation, i.e. no put files or $echo

If you are unfamiliar with GAMS, the GAMS Tutorial gives a quick introduction to the essentials of a GAMS model and the output provided when the model is solved. Examples of models in GAMS format can be found in the GAMS model library and an alphabetical index is also available.

An option file is needed to specify the AMPL solver to use on the reformulated model. This file can only contain AMPL option commands. For example, to use the LOQO solver, the option file would include the line

	option solver loqo;

Each line in the option file is treated as an AMPL statement by the reformulation tool. Therefore, option commands cannot span more than one line of text. Currently, the NEOS Server can only use optfile=1 with GAMS input. Therefore, any model that specifies a different options file will not work as intended.

The NEOS Server initially limits the amount of output generated in the listing file by turning off the symbol and unique element list, symbol cross references, and restricting the rows and columns listed to zero. This behavior can be changed by specifying the appropriate options in the model file. See the documentation on the modeling language for further information.

Additional Information

The GAMS/AMPL solver on the NEOS server is based on the GAMS/CONVERT tool written by GAMS Development Corporation. This tool is shipped with all GAMS systems of distribution 20.1 or newer. The GAMS/AMPL solver, which uses GAMS/CONVERT to translate the model into AMPL format, calls AMPL, and returns the solution of the AMPL solve to GAMS, can be run locally by downloading the GAMS/AMPL incremental update, placing the file into your GAMS installation directory, and installing it with the gamsinstprogram. To solve the models generated by GAMS/AMPL, you will also need to obtain a version of AMPL. The AMPL Student Edition can be downloaded from the indicated link.

Model file:

Options file:

The log file contains information generated by the algorithm during a solve. Checking the box will cause the log file to be included in the output returned.
Return log file:

Comments:

Put in priority queue

e-mail address:

Please do not click the 'Submit to NEOS' button more than once.

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