VF_autocorr VD_autocorr VE_autocorr
 VFb_autocorr VDb_autocorr VEb_autocorr
 Function autocorrelation function
 Syntax C/C++ #include void VF_autocorr( fVector Y, fVector X, ui size ); void VFb_autocorr( fVector Y, fVector X, ui size, fVector Buf ); C++ VecObj #include void vector::autocorr( const vector& X ); void vector::b_autocorr( const vector& X, vector& Buf ); Pascal/Delphi uses VFstd; procedure VF_autocorr( Y, X:fVector; size:UIntSize ); procedure VFb_autocorr( Y, X:fVector; size:UIntSize; Buf:fVector );
 CUDA function C/C++ #include int cudaVF_autocorr( fVector d_Y, fVector d_X, ui size ); void VFcu_autocorr( fVector h_Y, fVector h_X, ui size ); CUDA function Pascal/Delphi uses VFstd; function cudaVF_autocorr( d_Y, d_X:fVector; size:UIntSize ): IntBool; procedure VFcu_autocorr( h_Y, h_X:fVector; size:UIntSize );
 Description The autocorrelation function (ACF) of X is calculated and stored in Y in wrap-around order: Y0 to Ysize/2−1 contain the ACF for zero and positive lags. Beginning with the most negative lag in Ysize/2+1, the elements up to Ysize−1 contain the ACF for negative lags. Since this function assumes X to be periodic, the ACF for the most positive lag is identical to the ACF for the most negative lag. This element is stored as Ysize/2. To get the ACF into normal order, you may call VF_rotate( Y, Y, size, size/2 ); After that, the zero point is at the position size/2. In case X is non-periodic, you should avoid end effects by the methods described in connection with VF_convolve. Internally, VF_autocorr allocates and frees additional workspace memory. For repeated calls, this would be inefficient. In such a case, it is recommended to use VFb_autocorr instead. The size of Buf must be ≥ size. Additionally, Buf must be 128-bit (P8) or 256-bit (P9) aligned. This usually means you can only take a vector allocated by the VF_vector family as Buf.
 Error handling If size is not a power of 2, VF_FFT (on which VF_autocorr is based) complains "Size must be an integer power of 2" and the program is aborted.
 Return value none