where

at each step of integration the method proceeds through a set of intermediate steps. After each integration the RKF method provides not one, but two different solutions. If the solutions differe in more than a particular given threshold the ray step can be halved, and the integration repeated, providing a mean to control the accuracy of the solution. In order to prevent an infinite loop TRACEO stops the halving (and interrupts the calculations) if the sucessive comparisons of solutions fail to converge.

Orlando Camargo Rodríguez 2012-06-21