fft2di(3F)

NAME
     cfft2di, zfft2di - initialize the coefficient array for complex-to-
     complex 2D FFT modules.

SYNOPSYS
     FORTRAN SPECIFICATION
     subroutine CFFT2DI( n1, n2, coeff )
     integer                  n1, n2
     complex             coeff((n1+15) + (n2+15))

     subroutine ZFFT2DI( n1, n2, coeff )
     integer                  n1, n2
     double complex      coeff((n1+15) + (n2+15))

     C SPECIFICATION
     #include <fft.h>
     complex *cfft2di( int n1, int n2, complex *coeff);

     zomplex *zfft2di( int n1, int n2, zomplex *coeff);


DESCRIPTION
     Initialize the coefficient array which is used in the 2D FFT modules.
     This array contains the different twiddle factors and the factorization
     of N1 and N2 into prime numbers.
     As the FFT modules cfft2d or zfft2d only read the coeff array, it may be
     reused as long as necessary once it has been initialized.

     In C, if ptr is NULL, cfft2di or zfft2di returns a pointer to an
     allocated buffer.

     CFFT2DI should be used to initialize the coefficient array before any
     call to CFFT2D
     ZFFT2DI should be used to initialize the coefficient array before any
     call to ZFFT2D

PARAMETERS
     N1 - Integer, the first dimension size of the 2D sequence.
     Unchanged on exit.

     N2 - Integer, the second dimension size of the 2D sequence.
     Unchanged on exit.

     COEFF - Array (C or Fortran) or NULL pointer(C).

Example of Calling Sequence
     Initializing a coefficient array for complex-to-complex FFTs of size 200
     x 300.

     Fortran :
          complex coeff((200+15)+(300+15))
          call cfft2di( 200, 300, coeff)
     C :
          #include <fft.h>
          complex *coeff;
          coeff = cfft2di( 200, 300, NULL);

SEE ALSO
          fft, cfft2d, zfft2d