If you supply an optional file name with the extension.prm, that file contains the formatted list of parameters and their values that you do not want ILOG CPLEX to tune. That is, you want ILOG CPLEX to respect those parameter settings. If you do not supply a parameter file to the tune command, then all parameters are subject to tuning.

For example, if you have a model that you know has numerical issues, and you have already determined that you want to set the numerical emphasis parameter yourself, then a PRM file suitable for tuning your model would contain the following heading and parameter setting:

CPLEX Parameter File Version 11.0.0
CPX_PARAM_NUMERICALEMPHASIS      1

An easy way to generate a PRM file with a correct heading and fixed parameter settings is to read your model, set the parameters you wish, and write a PRM file from the Interactive Optimizer, with this command:

write filename.prm