3.4. FEATURES OF SPECIAL NETWORK MODELS

The transportation, assignment, and transshipment problems constitute a set of special network models in linear programming. They are special in the sense that they all lend themselves easily to the use of a flow diagram, and they all contain a From/To flow structure that suggests a convenient row-and-column layout in a spreadsheet. In particular, we can conveniently display the decision variables as an array in the spreadsheet. When we specify the variables for Solver, we do not enter a row of adjacent cells, which is the standard format. Instead, we enter an array, or in the case of the transshipment model, a pair of arrays. (This feature could obviously be generalized to cases in which we have three or more stages in the model.) With the array format at the heart of the model, the constraints involve limitations on totals across a row ....Box 3.1 summarizes the prominent features of special networks.