% Usage: r = d2cd3p(f,x,h)
% 3-point centered-difference formula for 2-nd derivative
%
% Input:
% f - Matlab inline function 
% x - point where the derivative is computed
% h - stepsize
%
% Output:
% r - computed value of the derivative
%
% Examples:
% r=d2cd3p(@sin,0,0.1);
% r=d2cd3p(@myfunc,0,.1);          here 'myfunc' is a user-defined function in M-file
% r=d2cd3p(inline('sin(x)'),0,0.1);
% r=d2cd3p(inline('sin(x)-cos(x)'),0,0.1);

function r = d2cd3p(f,x,h)
r = (f(x+h)-2*f(x)+f(x-h))/(h*h);