The routine CPXgetcallbackindicatorinfo accesses information about the indicator constraints of the presolved model during MIP callbacks. When there are indicator constraints, ILOG CPLEX creates a presolved model with indicator constraints in canonical form.

 Canonical Form
 (implying variable = { 0 | 1 }) IMPLIES (implied variable) R rhs
 

In that canonical form, rhs stands for righthand side and R stands for one of these relations:

• less than or equal to
• greater than or equal to
• equal to

In the original model, you may have indicator constraints in which the implied constraint has two or more variables. For example,

 x = 0 -> 3y + z <= 0
 

In contrast, in the canonical form, the implied constraint can have only one variable; moreover, its coefficient in the constraint must be 1 (one).

The argument which_info can assume one of the following values in a call to CPXgetcallbackindicatorinfo:

• CPX_CALLBACK_INFO_IC_NUM returns the number of indicator constraints.
• CPX_CALLBACK_INFO_IC_IMPLYING_VAR returns the index of the implying variable of the iindex-th indicator constraint. If the MIP callback parameter for the reduced LP (CPX_PARAM_MIPCBREDLP) is off (that is, set to CPX_OFF), the index is in terms of the original model, and if the index = -1, then the variable has been created by presolve. Otherwise, the index is in terms of the presolved model.
• CPX_CALLBACK_INFO_IC_IMPLIED_VAR returns the index of the impled variable of the iindex-th indicator constraint. If CPX_PARAM_MIPCBREDLP is set to CPX_OFF, the index is in terms of the original model, and if the index = -1, then the variable has been created by presolve. Otherwise, the index is in terms of the presolved model.
• CPX_CALLBACK_INFO_IC_SENSE returns the sense of the iindex-th indicator constraint.
• CPX_CALLBACK_INFO_IC_COMPL returns 0 (zero) if the iindex-th indicator constraint is not complemented, and 1 (one) otherwise.
• CPX_CALLBACK_INFO_IC_RHS returns the righthand side of the iindex-th indicator constraint.
• CPX_CALLBACK_INFO_IC_IS_FEASIBLE returns 1 (one) if the implying variable is not 0 (zero) or 1 (one), or if the iindex-th indicator constraint is satisfied at the current node; otherwise, it returns 0 (zero).