s of discount fares, and frequent flier), the airline has to de- cide how many passengers it is willing to book. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Capacity and Quality Tradeoffs Capacity and Quality Tradeoffs Figure 22.1 Two-dimensional feasible space. boundary of the feasible region, such as points Q and R, where all choices have some negative components. We use the term frontier to describe the set of points where all the decisions have some negative consequences. The frontier is not the entire boundary because such points as M and o are boundary points that are not frontier points as we are using the terms here. If we are trying to make x and y larger, then there are clearly all-good things we can do from points M and O. Points Q and R, on the other hand, have clear tradeoff consequences if we try to make changes from them. This geometric picture represents the state of a system where we make one variable better only by allowing some other variable to get worse. The casual term we use is "push down, pop up" because we can push one problem down only to have something else pop up elsewhere. It is an important part of decision making and decision support to understand what pops up when we push down on specific problems. Pipes, Bottlenecks, and Alternate Routes Suppose that we have a flow network from a source S to a target T. Each of the dots in Fig. 22.2 is a junction point, and each of the arrows has some flow capacity from one dot to another. It could be a telephone network, it could be water flowing through pipes, it could be cars driving on highways, or it could be a workflow plan for a factory. It does not matter what the application is; the network structure is the same. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights res