A note on accurate estimations of the local truncation error of polynomial methods for differential equations

We give sharp error estimations for the local truncation error of polynomial methods for the approximate solution of initial value problems. Our analysis is developed for second order differential equations with polynomial coefficients using the Tau Method as an analytical tool. Our estimates apply to approximations derived with the latter, with collocation and with techniques based on series expansions. An example on collocation is given, to illustrate the use of our estimates.