4. Dynamics
In this Section, we summarize briefly how projected dynamical systems theory can be
applied to the elastic demand transportation network equilibrium problem presented in Section
3 in order to provide the disequilibrium dynamics. The presentation here follows the
corresponding one in Nagurney (2004). Dupuis and Nagurney (1993) proved that, given
a variational inequality problem, there is a naturally associated dynamical system, the set
of stationary points of which coincides precisely with the set of solutions of the variational
inequality problem. The dynamical system, termed a projected dynamical system by Zhang
and Nagurney (1995), is non-classical in that its right-hand side, which is a projection operator,
is discontinuous. Nevertheless, it can be qualitatively analyzed and approximated
through discrete-time algorithms as described in Dupuis and Nagurney and also in the book
by Nagurney and Zhang (1996). Importantly, projected dynamical systems theory provides
insights into the travelers’ dynamic behavior in making their trip decisions and in adjusting
their route choices. Moreover, it provides for a powerful theory of stability analysis (cf.
Zhang and Nagurney (1996, 1997)). Other approaches to dynamic transportation network
problems can be found in Ran and Boyce (1996) and Mahmassani et al (1993). In particular,
here we focus on the disequilibrium dynamics and on what can be viewed as the day to day
adjustment until an equilibrium is reached.