|Function||Cross-correlation function of two vectors.|
|Syntax C/C++||#include <VFstd.h>
void VF_xcorr( fVector Z, fVector X, fVector Y, ui size );
|C++ VecObj||#include <OptiVec.h>
void vector<T>::xcorr( const vector<T>& X, const vector<T>& Y );
procedure VF_xcorr( Z, X, Y:fVector; size:UIntSize );
|Description||The cross-correlation function (CCF) of X and Y is calculated and stored in Z in wrap-around order: Z0 to Zsize/2-1 contain the CCF for zero and positive lags. Beginning with the most negative lag in Zsize/2+1, the elements up to Zsize-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 Zsize/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.
|Error handling||If size is not a power of 2, VF_FFT (on which VF_xcorr is based) complains "Size must be an integer power of 2" and the program is aborted.|
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