Hi, if I understand well you want to solve a system of ODEs in which appear a parameter tau that varies from 0 to 1. In the code you provide, it seems that you simply code the Euler method. You can simply replace this by a call to ode45. The value of tau has to be passed to the function codind the ODE by usinf a "global" instruction (equivalent to a COMMON in FORTRAN).
Thanks Richard, though i did not understand what you really want me to to do. i have ode45 matlab code for the two ode but don't know where precisely to insert it.