Besides the log-file parameter, ILOG CPLEX offers you output-channel parameters to give you finer control over when and where messages appear in the Interactive Optimizer. Output-channel parameters indicate whether output should or should not appear on screen. They also allow you to designate log files for message channels. The output-channel parameters do not affect the log-file parameter, so it is customary to use the command set logfile before the command set output channel value1 value2.

In the output-channel command, you can specify a channel: dialog, errors, logonly, results, and warnings. Table 8.2 summarizes the information carried over each channel.

The option value2 lets you specify a file name to redirect output from a channel.

Also in that command, value1 allows you to turn on or off output to the screen. When value1 is y, output is directed to the screen; when its value is n, output is not directed to the screen. Table 8.3 summarizes which channels direct output to the screen by default. If a channel directs output to the screen by default, you can leave value1 blank to get the same effect as set output channel y.