matthiasm@8: function acf = ftacf(x)
matthiasm@8: 
matthiasm@8: 
matthiasm@8: x = x(:);
matthiasm@8: 
matthiasm@8: [M,N] = size(x);
matthiasm@8: 
matthiasm@8: X = fft(x,2^nextpow2(2*M-1));
matthiasm@8: acf = ifft(X.*conj(X));
matthiasm@8: 
matthiasm@8: acf = acf(1:M)./[M:-1:1]';