% What is the purpose of this program?
% Which one of f1, f2 is more correct? why?
% Most of the newer matlab contains vpa.
% If yours doesn't, try google 'matlab vpa'

a = 3.e-8;
h = a/16;
x = -a:h:a;
f1 = exp(x) - cos(x) - x;
f2 = x.^2 + x.^3/6;
figure(1), plot(x,f1,'x',x,f2,'o')

x_longer = vpa(x,24);
f_longer = exp(x_longer)-cos(x_longer) - x_longer;
f0 = double(f_longer);

figure(2), plot(x,f0,x,f1,'x',x,f2,'o')