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ILOG CPLEX 11.0 User's Manual

ILOG CPLEX 11.0 User's Manual

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16Using Special Ordered Sets (SOS)<strong>ILOG</strong> <strong>CPLEX</strong> enables you to define special ordered sets (SOSs) in the model of yourproblem as a way to specify integrality conditions. The following sections tell you moreabout special ordered sets.◆ What Is a Special Ordered Set (SOS)? on page 329◆ Example: SOS Type 1 for Sizing a Warehouse on page 330◆ Declaring SOS Members on page 331◆ Example: Using SOS and Priority on page 331What Is a Special Ordered Set (SOS)?A special ordered set (SOS) is an additional way to specify integrality conditions in a model.In particular, a special ordered set is a way to restrict the number of nonzero solution valuesamong a specified set of variables in a model. There are various types of SOS:◆◆SOS Type 1 is a set of variables where at most one variable may be nonzero.SOS Type 2 is a set of variables where at most two variables may be nonzero. If twovariables are nonzero, they must be adjacent in the set.The members of a special ordered set (SOS) individually may be continuous or discretevariables in any combination. However, even when all the members are themselves<strong>ILOG</strong> <strong>CPLEX</strong> <strong>11.0</strong> — USER’ S MANUAL 329

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