Probing

Describes probing, a technique that fixes binary variables and analyzes the implications.

The probing feature can help in many different ways on difficult models. Probing is a technique that looks at the logical implications of fixing each binary variable to 0 (zero) or 1 (one). It is performed after preprocessing and before the solution of the root relaxation. Probing can be expensive, so this parameter should be used selectively. On models that are in some sense easy, the extra time spent probing may not reduce the overall time enough to be worthwhile. On difficult models, probing may incur very large runtime costs at the beginning and yet pay off with shorter overall runtime. When you are tuning performance, it is usually because the model is difficult, and then probing is worth trying.

At the default setting of the probing parameter (0 (zero)), CPLEX will automatically decide an appropriate level of probing. Setting the probing parameter to 1, 2, or 3, results in increasing levels of probing performed beyond the default level. A setting of -1 results in no probing being performed.

To activate an increasing level of probing use the MIP probing level parameter:

• In the Interactive Optimizer, use the command set mip strategy probe i.

• In Concert Technology, set the integer parameter Probe.

• In the Callable Library, set the integer parameter CPX_PARAM_PROBE.