LOGMIP

The NEOS Server offers EMP (Extended Mathematical Programming), an (experimental) framework for automated mathematical programming reformulations through the solver LogMip 2.0 for solving linear and nonlinear disjunctive programming problems involving binary variables and disjunction definitions for modeling discrete choices. While the modeling and solution of these disjunctive optimization problems has not yet reached the same stage of maturity and reliability as LP, MIP and NLP modeling, these problems have a rich area of applications.

LogMIP 2.0 has been developed by Dr. Aldo Vecchietti from INGAR (Santa Fe, Argentina) and Professor Ignacio E. Grossmann from Carnegie Mellon University (Pittsburgh, USA).

Using the NEOS Server for LOGMIP/GAMS

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:

• It must be self contained, i.e., no $include or $batinclude statements.
• It may not execute external programs, i.e., no $call or execute statements.
• No file creation, i.e. no put files or $echo except for a file named 'results.txt'. Other files created in the GAMS model file will be deleted.

If you are unfamiliar with GAMS, the GAMS Documentation includes a GAMS Tutorial and User's Guide. Examples of models in GAMS format can be found in the GAMS model library.

By default, the NEOS Server 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 GAMS output for further information.

You may optionally submit an options file if you wish to override the default parameter settings for the solver. 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.