f = inline('sin(x)');
 fppTrue = inline('-sin(x)');
 h = 0.1;
 x = pi/3;
 
 fprintf('   h        Abs. Error\n');
 fprintf('=========================\n');
 for i = 1:6
     fpp = (f(x+h) - 2*f(x) + f(x-h))/h^2;
     fprintf('%7.1e     %8.1e\n',h,abs(fpp - fppTrue(x)))
     h = h/10;
 end