function zeta = whiterestest(res)

Mgdl = 8;
N = length(res);
Rr = zeros(1,Mgdl+1);

for indx=1:Mgdl+1,
    Rr(indx) = ( (res(1:N-Mgdl))' * res(indx:N+indx-1-Mgdl) )/(N-Mgdl);
end;

zeta = (N-Mgdl) *( Rr(2:Mgdl+1)*( Rr(2:Mgdl+1)' ) )/(Rr(1)*Rr(1));

return