Description | The cross-correlation function (CCF) of X and Y is calculated and stored in Z in wrap-around order: Z_{0} to Z_{size/2-1} contain the CCF for zero and positive lags. Beginning with the most negative lag in Z_{size/2+1}, the elements up to Z_{size-1} contain the CCF for negative lags. Since this function assumes X to be periodic, the CCF for the most positive lag is identical to the CCF for the most negative lag. This element is stored as Z_{size/2}.
To get the CCF into normal order, you may call
VF_rotate( Z, Z, size, size/2 );
After that, the zero point is at the position size/2.
In case X is non-periodic, end effects should be avoided by the methods described in connection with *VF_convolve*.
About special versions with the prefixes *VFp_, VFs_* and *VFl_*, consult chapter 4.8. |