As indicated in Fig. 3.13, these required amounts are 50 for F1, 40 for F2, - 30 for W1, and-60 for W2.
What is the required amount for DC? All the unit produced at the factories are ultimately needed at the warehouses, so any units shipped from the factories to the distribution center should be forwarded to the warehouses. Therefore,the total amount shipped from the distribution center to the warehouses should equal the total amount shipped from the factories to the distribution center. In other words, the difference of these two shipping amounts (the required amount for the net flow constraint) should be zero.
Since the objective is to minimize the total shipping cost, the coefficients for the objective function come directly from the unit shipping costs given in Fig. 3.13. Therefore, by using money units of hundreds of dollars in this objective function, the complete linear programming model is