Estimation of the parameters in the gravity model for trip distribution : A new method and solution algorithm

For the unique determination of the parameters in the doubly constrained gravity model with exponential friction function two approaches are common: (1) entropy maximization and (2) application of a travel cost budget. This paper shows by making use of geometric programming that both of these approaches are equivalent with another natural criterion: the minimization of the deviation between the observed [t_1j] and the estimated [x_1j] table for a base year. By means of calculating the derivative of total cost as a function of σ the construction of an efficient algorithm for estimation of σ is made possible.