Generic rows and columns do not correspond exactly to the constraints and decision variables in a mathematical formulation. In a mathematical formulation a constraint or a decision variable represents a class of constraints or decision variables. A decision variable may appear more than once in a constraint. For instance, in a multitimeperiod model a material balance constraint may include two instances of the decision variable for stock: at the end of the preceding time period, z_{p,t1}; and at the end of the current time period, z_{pt} : MBALpt: z_{p,t1} + y_{pt} – z_{pt} = 0 for all p,t In SCM Planning this can be implemented in several different ways. One of them is to define one generic column for the stock for the current time period and another generic column for the stock for the preceding time period. Each of these generates columns with the same names, e.g. Z.CR.1 might be generated from the generic column for:
Thus generic rows and columns can be considered as fragments of a logical constraint or decision variable as defined in a mathematical formulation. In many cases there is a direct correspondence between generic rows and columns and the logical constraints and decision variables. But in other cases two or more generic rows or columns are required to represent the logical constraint or decision variable. You define a generic row or column by specifying it in the set ROW or COL and defining its entries in the table ROWS or COLS. The Code of the entry in ROW or COL should be unique in that set but is not used in the names of the rows or columns which are generated for it. Similarly the Description in ROW or COL is merely descriptive; as it is usually displayed in the tables indexed by ROW or COL, it should list the identifier for the generic row or column and the subscripts which index it. The rows or columns which are generated for a generic row or column are determined by the entries in the table ROWS or COLS. For each element of ROW or COL you specify:

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