Add a new general constraint of type GRB_GENCONSTR_ABS to a model. Note that, due to our lazy update approach, the new constraint won't actually be added until you update the model (using GRBupdatemodel), optimize the model (using GRBoptimize), or write the model to disk (using GRBwrite).
An ABS constraint states that the resultant variable should be equal to the absolute value of the argument variable .
A non-zero return value indicates that a problem occurred while adding the general constraint. Refer to the Error Code table for a list of possible return values. Details on the error can be obtained by calling GRBgeterrormsg.
model: The model to which the new general constraint should be added.
name: Name for the new general constraint. This argument can be NULL, in which case the constraint is given a default name.
resvar: The index of the resultant variable whose value will be to equal the absolute value of the argument variable.
argvar: The index of the argument variable for which the absolute value will be taken.
/* x5 = abs(x1) */ error = GRBaddgenconstrAbs(model, "absconstr", 5, 1);