Xi-Language Reference: Fast Fourier Transform

    • fft (Multivariate fast fourier transform)
    • rev_fft (Multivariate fast fourier transform)

    fft (Multivariate fast fourier transform)

    Parameters

              fft ( array, index... )
    
              Types: array                  complex[]
                     index...               int
    

    Return

              complex[]  (fast fourier transform, space to frequency)
    

    Description

    fft performs a multivariate complex fast fourier transform to go form space to frequency using mixed-radix fast fourier transform algorithm. The parameter array contains a multidimensional array for which the FFT should be computed. The parameters index1, index2 etc. determine the indices over which the FFT will be performed. If these parameters are omitted the function fft computes the complete FFT of the input array.

    Example

     (  1)>a=dincarr(3,3);
     (  2)>b=fft(a);
     (  3)>e=fft(a,0,1);
     (  4)>c=fft(a,0); 
     (  5)>d=fft(c,1);
                  now b, d and e are equal        
    

    See also

    rev_fft

    Reference

    This function is based on the subroutine multifft in the GO collection.(By R.C. Singleton, Stanford Research Institute, Sept. 1968).

    rev_fft (Multivariate fast fourier transform)

    Parameters

              rev_fft ( array, index... )
    
              Types: array                  complex[]
                     index...               int
    

    Return

              complex[]  (fast fourier transform, frequency to space)
    

    Description

    rev_fft performs a multivariate complex fast fourier transform to go form frequency to space using mixed-radix fast fourier transform algorithm. The parameter array contains a multidimensional array for which the FFT should be computed. The parameters index1, index2 etc. determine the indices over which the FFT will be performed. If these parameters are omitted the function fft computes the complete FFT of the input array.

    Example

     (  1)>a=dincarr(3,3);
     (  2)>b=rev_fft(a);
     (  3)>c=rev_fft(a,0);
     (  4)>e=fft(a,0,1); 
     (  5)>d=rev_fft(fft(a,0),0);
                  now e is equal b and d is equal a        
    

    See also

    fft

    Reference

    This function is based on the subroutine multifft in the GO collection. (By R.C. Singleton, Stanford Research Institute, Sept. 1968).
    © 1995 by Bodo Junglas, Klaus Spanderen and Fabian Weis
    - Last revised: Wed Jun 19 16:58:32 1996