Contents
zfftd - initialize the trigonometric weight and factor
tables or compute the inverse Fast Fourier Transform of a
double complex sequence.
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, doub-
lecomplex *x, double *y, double *trigs, long
*ifac, double *work, long *lwork, long *ierr);
zfftd initializes the trigonometric weight and factor tables
or computes 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) com-
plex 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.
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 starting 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 com-
puted when the routine is called with IOPT = 0 and
they are used in subsequent calls when IOPT = 1.
Unchanged on exit.
IFAC (input/output)
Integer array of dimension at least 128 that con-
tains 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 allo-
cate 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
fft