function [t,y] = euler( f, tspan, y0, n)
%EULER Apply Euler's method to solve y' = f(y,t), y(a) = y0,
%  on the interval a <= t <= b with n steps.
    a = tspan(1);
    b = tspan(2);
    h = (b-a)/n;
    t = a:h:b;
    y(1) = y0;
    for j = 1:n
        y(j+1) = y(j) + h.*f(t(j),y(j));
    end
end