fft3dui(3F)

NAME
     scfft3dui, dzfft3dui - initialize the coefficient array for real-to-
     complex 3D FFT modules.

SYNOPSYS
     FORTRAN SPECIFICATION
     subroutine SCFFT3DUI( n1, n2, n3, coeff )
     integer                  n1, n2, n3
     real           coeff((n1+15) + 2*(n2+15) + 2*(n3+15))

     subroutine DZFFT3DUI( n1, n2, n3, coeff )
     integer                  n1, n2, n3
     real*8              coeff((n1+15) + 2*(n2+15) + 2*(n3+15))

     C SPECIFICATION
     #include <fft.h>
     float *scfft3dui( int n1, int n2, n3, float *coeff);

     double *dzfft3dui( int n1, int n2, n3, double *coeff);


DESCRIPTION
     Initialize, the coefficient array which is used in the 3D FFT modules.
     This array contains the different twiddle factors and the factorization
     of N1, N2 and N3 into prime numbers.
     As the FFT modules scfft3d or dzfft3d only read the coeff array, it may
     be reused as many times as necessary once it has been initialized.

     In C, if ptr is NULL, scfft3dui or dzfft3dui returns a pointer to an
     allocated buffer.

     SCFFT3DUI should be used to initialize the coefficient array before any
     call to SCFFT3DU
     DZFFT3DUI should be used to initialize the coefficient array before any
     call to DZFFT3DU

PARAMETERS
     N1 - Integer. Specifies the size of the first dimension of the 3D
     sequence to be transformed.  Unchanged on exit.

     N2 - Integer. Specifies the size of the second dimension of the 3D
     sequence to be transformed.  Unchanged on exit.

     N3 - Integer. Specifies the size of the third dimension of the 3D
     sequence to be transformed.  Unchanged on exit.

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

Example of Calling Sequence
     Initializing a coefficient array for real-to-complex FFTs of size 200 x
     300 x 125.
     Fortran :
          real coeff((200+15)+2*(300+15)+2*(125+15))
          call scfft3dui( 200, 300, 125, coeff)

     C :
          #include <fft.h>
          float *coeff;
          coeff = scfft3dui( 200, 300, 125, NULL);

SEE ALSO
          fft, scfft3du, dzfft3du