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NEOS Interfaces to CONOPT

WWW Form & Sample Submissions


The NEOS Server offers CONOPT for the solution of nonlinearly constrained optimization problems in GAMS format.

CONOPT is a feasible path method based on the GRG algorithm. CONOPT is well-suited to models with very nonlinear constraints. It is a fast method for finding a first feasible solution that is particularly well-suited to models with few degrees of freedom. Also, for models where many equations can be solved one by one, CONOPT will take advantage of this property. Similarly, CONOPT eliminates from the model intermediate variables only used to define objective function terms and moves the constraints into the objective function.

CONOPT is developed and maintained by ARKI Consulting and Development A/S in Bagsvaerdvej, Denmark. For more information, visit the CONOPT website.

Using the NEOS Server with CONOPT

The user must submit a model in GAMS format to solve a nonlinear programming 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.
  • It may not create files, i.e., no put files or $echo statements.

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 and an alphabetical index is available.

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.

Web Submission Form
Model File
To submit a nonlinear programming problem specified in the GAMS modeling language, you need to specify the absolute path to the GAMS file on your system.
Options File
The Options file is optional and requires that the statement <modelname>.optfile = 1 ; exist before the solve statement in your model file. Only optfile = 1 is supported, however, options also may be specified within the model input file (see the GAMS documentation).
GDX File
The GDX file is an optional file for inputs. It will be renamed in.gdx. The model must include "$GDXIN in.gdx" to load this file.
Return GDX output
If the box is checked, the solver will return a compressed GDX file that contains all symbols in the model.
Return log file
If the box is checked, the log file containing information generated by the solver will be returned with the output.
You may enter additional comments here, for example, to identify the data for your own information. These comments will be returned with your results.
Additional Settings
Dry run: generate job XML instead of submitting it to NEOS
Short Priority: submit to higher priority queue with maximum CPU time of 5 minutes
E-Mail address:
Please do not click the 'Submit to NEOS' button more than once.