Solution options
After solving a problem, the Interactive Optimizer supports these additional options.
Here are some of the basic options in solving linear programming problems. Although the example in this tutorial does not make use of these options, you will find them useful when handling larger, more realistic problems.
For detailed information about performance options, refer to the CPLEX User’s Manual.
Filing iteration logs
Every time CPLEX solves a problem, much of the information
appearing on the screen is also directed into a log file. This file
is automatically created by CPLEX with the name cplex.log .
If there is an existing cplex.log file
in the directory where CPLEX is launched, CPLEX will append the current
session data to the existing file. If you want to keep a unique log
file of a problem session, you can change the default name with the set logfile command.
(See the CPLEX User’s Manual.)
The log file is written in standard ASCII format and can be edited
with any text editor.
Re-solving
You may re-solve the problem by reissuing the optimize command.
CPLEX restarts the solution process from the previous optimal basis,
and thus requires zero iterations. If you do not wish to restart the
problem from an advanced basis, use the set advance command
to turn off the advanced start indicator.
Remember that a problem must be present in memory (entered
via the enter command or read from a file)
before you issue the optimize command.
Using alternative optimizers
In addition to the optimize command,
CPLEX can use the primal simplex optimizer (primopt command),
the dual simplex optimizer (tranopt command),
the barrier optimizer (baropt command)
and the network optimizer (netopt command).
Many problems can be solved faster using these alternative optimizers,
which are documented in more detail in the CPLEX User’s Manual. If you
want to solve a mixed integer programming problem, the optimize command
is equivalent to the mipopt command.
Interrupting the optimization
Our short example was solved very quickly. However, larger
problems, particularly mixed integer problems, can take much longer.
Occasionally it may be useful to interrupt the optimization process.
CPLEX allows such interruptions if you use control-c .
(The control and c keys
must be pressed simultaneously.) Optimization is interrupted, and
CPLEX issues a message indicating that the process was stopped and
displays progress information. If you issue another optimization command
in the same session, CPLEX will resume optimization from where it
was interrupted.