Data Dictionary System: Developers Fortran FFT (fft

Indexfft_nrfft5
fft_nrfft5odd
fft_ccfftm
fft_ccfft2d
fft_ccfft3d
fft_crfftm
fft_crfft2d
fft_crfft3d
fft_rcfftm
fft_rcfft2d
fft_rcfft3d
fft_zzfftm
fft_zzfft2d
fft_zzfft3d

fft_ccfft3d - complex-complex 3D FFT

SYNOPSIS

#include <fft.h> (fixed-format sources)
#include <f90fft.h> (free-format sources)

integer function fft_ccfft3d(isign, scale, n1, n2, n3, ld1, ld2, cdata, iopt)

integer isign
real scale
integer n1
integer n2
integer n3
integer ld1
integer ld2
complex cdata(ld1,ld2,n3)
integer iopt

DESCRIPTION

The function, "fft_ccfft3d", performs a complex-to-complex 3D FFT -- essentially a 1D FFT along the first axis, followed by another 1D FFT along the second axis, followed by another 1D FFT along the third axis.

INPUT

The parameter, "isign", specifies the sign of complex exponential. It expects a "1" or "-1"; a value of zero "0" is invalid.

The parameter, "scale", specifies the scale factor to be applied to the data.

The size parameters, "n1", "n2" and "n3", specifies the FFT sizes. These must be setup as mixed radix values (must be even) in order to allow the FFT's to be more efficient. It is recommended to use fft_nrfft5 to calculate these values.

The leading dimension parameters, "ld1" and "ld2", specify the leading dimensions of the complex array. If they are the same as the FFT sizes, "n1" and "n2" respectively, then the routine will be more efficient.

The complex array, "cdata", is the I/O array for the FFT's. This is performed "in place".

The parameter, "iopt", is used to specify any other information that is unique to a specific FFT implementation. Currently, the use is for specifying whether to measure or estimate the FFT's when using FFTW routines. The "fft.h" header defines FFT_MEASURE and FFT_ESTIMATE, besides defining the FFT functions, as integer.

OUTPUT

The fft results are returned in the complex data array and the returned value is zero "0" if successful. A value of "-1" is returned if the arguments are invalid. Otherwise, a value unique to each FFT implementation is returned.

EXAMPLE

      integer :: fft_size1, fft_size2, fft_size3, fft_flag
      integer :: isign, ier
      real    :: fft_scale
      complex, allocatable :: cdata(:,:,:)

      fft_size1 = fft_nrfft5(100)
      fft_size2 = fft_nrfft5(50)
      fft_size3 = fft_nrfft5(200)

      allocate(cdata(fft_size1, fft_size2, fft_size3))

      ...
      fft_flag = FFT_ESTIMATE

      ! forward FFT
      isign = -1
      fft_scale = 1.0D+00/(dble(fft_size1)*dble(fft_size2)*dbl(fft_size3))
      ier = fft_ccfft3d(isign, fft_scale, fft_size1, fft_size2, fft_size3, fft_size1, fft_size2, cdata, fft_flag)

      ! inverse FFT
      isign = 1
      fft_scale = 1.0
      ier = fft_ccfft3d(isign, fft_scale, fft_size1, fft_size2, fft_size3, fft_size1, fft_size2, cdata, fft_flag)

AUTHOR

Phuong Vu, HPC
Jerry Ehlers, EPTG