The above formulations of objective functions for expressing likelihood require additional constraints in order to be
complete (Van Zuylen and Willumsen, 1978 and Willumsen 1980). The simplest of these constraints indicate that the
sum of all trips crossing a given link must be equal to the link flow on that link, as indicated in Equation 6. As will be
shown later, the simplest mechanism, for including the above constraints in the earlier objective functions, is to utilize
Lagrange multipliers. These multipliers permit an objective function with equality constraints to be transformed into an
equivalent unconstrained objective function.