Special-ordered sets (SOS)
Types of constraints in optimization models. SOS of type 1 require that only one variable in the set maybe nonzero; SOS of type 2 require that only two variables in the set maybe nonzero and they must be adjacent. SOS of type 1 are used in problems in which the variables in the set are binary and only one of them can be equal to one (e.g., assignment of personnel). SOS of type 2 occur when transforming a separable-programming problem into an equivalent linear structure. Special computational approaches are used to simplify the handling of both types of SOSproblems. Separable-programming problem.