function x1 = taystep( t, x, h )
%
% Use 3rd order Taylor series to advance
% x(t) to x(t+h), where x' = x^2 - t.
%
xp = x.^2 - t;
xpp = 2*x.*xp - 1;
xppp = 2*xp.^2 + 2*x.*xpp;
x1 = x + xp*h + xpp*h^2/2 + xppp*h^3/6;
