zfftd(3P) Sun Performance Library zfftd(3P)NAMEzfftd - initialize the trigonometric weight and factor tables or com‐
pute the inverse Fast Fourier Transform of a double complex sequence.
SYNOPSIS
SUBROUTINE ZFFTD(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER IOPT, N, IFAC(*), LWORK, IERR
DOUBLE COMPLEX X(*)
DOUBLE PRECISION SCALE, Y(*), TRIGS(*), WORK(*)
SUBROUTINE ZFFTD_64(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER*8 IOPT, N, IFAC(*), LWORK, IERR
DOUBLE PRECISION SCALE, Y(*), TRIGS(*), WORK(*)
DOUBLE COMPLEX X(*)
F95 INTERFACE
SUBROUTINE FFT(IOPT, N, [SCALE], X, Y, TRIGS, IFAC, WORK, [LWORK], IERR)
INTEGER, INTENT(IN) :: IOPT, N
INTEGER, INTENT(IN), OPTIONAL :: LWORK
REAL(8), INTENT(IN), OPTIONAL :: SCALE
COMPLEX(8), INTENT(IN), DIMENSION(:) :: X
REAL(8), INTENT(OUT), DIMENSION(:) :: Y
REAL(8), INTENT(INOUT), DIMENSION(:) :: TRIGS
INTEGER, INTENT(INOUT), DIMENSION(:) :: IFAC
REAL(8), INTENT(OUT), DIMENSION(:) :: WORK
INTEGER, INTENT(OUT) :: IERR
SUBROUTINE FFT_64(IOPT, N, [SCALE], X, Y, TRIGS, IFAC, WORK, [LWORK], IERR)
INTEGER(8), INTENT(IN) :: IOPT, N
INTEGER(8), INTENT(IN), OPTIONAL :: LWORK
REAL(8), INTENT(IN), OPTIONAL :: SCALE
COMPLEX(8), INTENT(IN), DIMENSION(:) :: X
REAL(8), INTENT(OUT), DIMENSION(:) :: Y
REAL(8), INTENT(INOUT), DIMENSION(:) :: TRIGS
INTEGER(8), INTENT(INOUT), DIMENSION(:) :: IFAC
REAL(8), INTENT(OUT), DIMENSION(:) :: WORK
INTEGER(8), INTENT(OUT) :: IERR
C INTERFACE
#include <sunperf.h>
void zfftd_ (int *iopt, int *n, double *scale, doublecomplex *x, double
*y, double *trigs, int *ifac, double *work, int *lwork, int
*ierr);
void zfftd_64_ (long *iopt, long *n, double *scale, doublecomplex *x,
double *y, double *trigs, long *ifac, double *work, long
*lwork, long *ierr);
PURPOSEzfftd initializes the trigonometric weight and factor tables or com‐
putes the inverse Fast Fourier Transform of a double complex sequence
as follows:
N-1
Y(k) = scale * SUM W*X(j)
j=0
where
k ranges from 0 to N-1
i = sqrt(-1)
isign = 1 for inverse transform or -1 for forward transform
W = exp(isign*i*j*k*2*pi/N)
In complex-to-real transform of length N, the (N/2+1) complex input
data points stored are the positive-frequency half of the spectrum of
the Discrete Fourier Transform. The other half can be obtained through
complex conjugation and therefore is not stored. Furthermore, due to
symmetries the imaginary of the component of X(0) and X(N/2) (if N is
even in the latter) is assumed to be zero and is not referenced.
ARGUMENTS
IOPT (input)
Integer specifying the operation to be performed:
IOPT = 0 computes the trigonometric weight table and factor
table
IOPT = 1 computes inverse FFT
N (input)
Integer specifying length of the input sequence X. N is most
efficient when it is a product of small primes. N >= 0.
Unchanged on exit.
SCALE (input)
Double precision scalar by which transform results are
scaled. Unchanged on exit. SCALE is defaulted to 1.0D0 for
F95 INTERFACE.
X (input) On entry, X is a double complex array whose first (N/2+1)
elements are the input sequence to be transformed.
Y (output)
Double precision array of dimension at least N that contains
the transform results. X and Y may be the same array start‐
ing at the same memory location. Otherwise, it is assumed
that there is no overlap between X and Y in memory.
TRIGS (input/output)
Double precision array of length 2*N that contains the
trigonometric weights. The weights are computed when the
routine is called with IOPT = 0 and they are used in subse‐
quent calls when IOPT = 1. Unchanged on exit.
IFAC (input/output)
Integer array of dimension at least 128 that contains the
factors of N. The factors are computed when the routine is
called with IOPT = 0 and they are used in subsequent calls
where IOPT = 1. Unchanged on exit.
WORK (workspace)
Double precision array of dimension at least N. The user can
also choose to have the routine allocate its own workspace
(see LWORK).
LWORK (input)
Integer specifying workspace size. If LWORK = 0, the routine
will allocate its own workspace.
IERR (output)
On exit, integer IERR has one of the following values:
0 = normal return
-1 = IOPT is not 0 or 1
-2 = N < 0
-3 = (LWORK is not 0) and (LWORK is less than N)
-4 = memory allocation for workspace failed
SEE ALSO
fft
6 Mar 2009 zfftd(3P)
