C Parameter Examples

The C interface defines a symbolic constant for each parameter. The symbolic constant name is prefixed by GRB_type_PAR_, where type is either INT, DBL, or STR. This is followed by the capitalized parameter name. For example, the symbolic constant for the integer Threads parameter (found in C header file gurobi_c.h) is:

#define GRB_INT_PAR_THREADS "Threads"

The routine you use to modify a parameter value depends on the type of the parameter. For a double-valued parameter, you would use GRBsetdblparam.

Recall that each model gets its own copy of the environment when it is created. Parameter changes to the original environment therefore have no effect on existing models. You'll need to use GRBgetenv to retrieve the environment associated with a particular model if you want to change a parameter for that model.

To set the TimeLimit parameter for a model, you'd do:

  error = GRBsetdblparam(GRBgetenv(model), GRB_DBL_PAR_TIMELIMIT, 100.0);

If you'd prefer to use a string for the parameter name, you can also do:

  error = GRBsetdblparam(GRBgetenv(model), "TimeLimit", 100.0);
The case of the string is ignored, as are underscores. Thus, TimeLimit and TIME_LIMIT are equivalent.

Use GRBgetdblparam to query the current value of a (double) parameter:

  double currentvalue;
  error = GRBgetdblparam(modelenv, "TimeLimit", &currentvalue);