cfft1d,zfft1d(3F)					     cfft1d,zfft1d(3F)

NAME    [Toc]    [Back]

     cfft1d, zfft1d - 1D, Real Complex-to-Complex, Fast	Fourier	Transforms.

SYNOPSYS    [Toc]    [Back]

     Fortran :
     subroutine	cfft1d(	sign, n, array,	inc, coeff )
	  integer sign,	n, inc
	  complex array(0:(N-1)*inc), coeff(n+15)
     subroutine	zfft1d(	sign, n, array,	inc, coeff )
	  integer sign,	n, inc
	  double complex array(0:(N-1)*inc), coeff(n+15)

     C :
     #include <fft.h>
     int cfft1d	( int sign, int	n, complex *array,
	       int inc,	complex	*coeff);
     int zfft1d	( int sign, int	n, zomplex *array,
	       int inc,	zomplex	*coeff);

DESCRIPTION    [Toc]    [Back]

     cfft1d and	zfft1d compute the Fourier transform of	a complex sequence.
     The k-th index F(k) of the	Fourier	transform of a real sequence f(i) is
     equal to:
	  F(k) = Sum ( W^(i*k) * f(i) ), for i =0, ...,	(N-1)
	       W = exp(	(Sign*2*sqrt(-1)*PI) / N )


     The Direct	Fourier	transform is performed in-place, so the	input sequence
     is	overwritten by its Fourier transform.

PARAMETERS    [Toc]    [Back]

     SIGN Integer specifying which sign	to be used for the expression of W
     (see above) - must	be either +1 or	-1.
     The choice	for the	sign of	the direct transform is	just a matter of
     convention. For the reverse transform, it must be the opposite.
     Unchanged on exit.

     N Integer,	the number of samples in each sequence.
     Unchanged on exit.

     ARRAY Array containing the	samples	of the sequence	to be transformed.
     On	input, the element "i" of the sequence is stored as A(i*inc) in
     Fortran , and A[i*inc] in C.
     On	exit, the array	is overwritten by its transform.

     INC Integer, increment between two	consecutive elements of	a sequence.
     Unchanged on exit.

     COEFF Array of at least ( N + 15 )	elements.  On entry it contains	the
     Sines/Cosines and factorization of	N. COEFF needs to be initialized with
     a call to cfft1di or zfft1di.



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cfft1d,zfft1d(3F)					     cfft1d,zfft1d(3F)



     Unchanged on exit.


Example	of Calling Sequence
     Direct Fourier Transform of a sequence of 1024 complex values.  Elements
     of	sequence are stored with increment (stride) 1.
     Fortran
	  complex array(0:1024-1), coeff(1024+15)
	  call cfft1di(	1024, coeff)
	  call cfft1d( -1, 1024, array,	1, coeff)

     C
	  #include <fft.h>
	  complex array[1024], *coeff;
	  coeff	= cfft1di( 1024, NULL);
	  cfft1d( -1, 1024, array, 1, coeff);

SEE ALSO    [Toc]    [Back]

     fft, cfft1di, zfft1di, cscal1d, zscal1d


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