5.3 Common Features
Hidden in our models of these problems are a number of assumptions. The usefulness of a model
is directly related to how close reality matches up with these assumptions.
The rst assumption is due to the linear form of our functions. Since the ob jective is linear, the
contribution to the ob jective of any decision variable is proportional to the value of the decision
variable. Producing twice as much of a product produces twice as much prot; buying twice as
many pages of ads costs twice as much. This is the Proportionality Assumption. Furthermore, the contribution of a variable to the ob jective is independent of the values of
the other variables. One notebook computer is worth $750, independent of how many desktop
computers we produce. This is the Additivity Assumption.