The word linear indicates that the criterion
for selecting the best values of the decision variables can be
described by a linear function of these variables; that is, a mathematical
function involving only the first powers of the variables
with no cross-products. For example, 23X2 and 4X16 are valid
decision variables, while 23X2
2, 4X16
3, and (4X1 * 2X1) are not