%Input - y'= f is the function
% - a and b are the left and right endpoints
% - ya is the initial condition y(a)
% - M is the number of steps
%Output - H=[T' Y'] where T is the vector of abscissas and
% - Y is the vector of ordinates
%If f is defined as an M-file function use the @ notation
% call E=heun(@f,a,b,ya,M).
%If f is defined as an anonymous function use the
% call E=heun(f,a,b,ya,M).
% NUMERICAL METHODS: Matlab Programs
% (c) 2004 by John H. Mathews and Kurtis D. Fink
% Complementary Software to accompany the textbook:
% NUMERICAL METHODS: Using Matlab, Fourth Edition
% ISBN: 0-13-065248-2
% Prentice-Hall Pub. Inc.
% One Lake Street
% Upper Saddle River, NJ 07458