dfftz(3P) Sun Performance Library dfftz(3P)NAMEdfftz - initialize the trigonometric weight and factor tables or com‐
pute the forward Fast Fourier Transform of a double precision sequence.
SYNOPSIS
SUBROUTINE DFFTZ(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER IOPT, N, IFAC(*), LWORK, IERR
DOUBLE COMPLEX Y(*)
DOUBLE PRECISION X(*), SCALE, TRIGS(*), WORK(*)
SUBROUTINE DFFTZ_64(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER*8 IOPT, N, IFAC(*), LWORK, IERR
DOUBLE COMPLEX Y(*)
DOUBLE PRECISION X(*), SCALE, TRIGS(*), WORK(*)
F95 INTERFACE
SUBROUTINE FFT(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, [LWORK], IERR)
INTEGER, INTENT(IN) :: IOPT
INTEGER, INTENT(IN), OPTIONAL :: N, LWORK
REAL(8), INTENT(IN), OPTIONAL :: SCALE
REAL(8), INTENT(IN), DIMENSION(:) :: X
COMPLEX(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
INTEGER(8), INTENT(IN), OPTIONAL :: N, LWORK
REAL(8), INTENT(IN), OPTIONAL :: SCALE
REAL(8), INTENT(IN), DIMENSION(:) :: X
COMPLEX(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 dfftz_ (int *iopt, int *n, double *scale, double *x, doublecomplex
*y, double *trigs, int *ifac, double *work, int *lwork, int
*ierr);
void dfftz_64_ (long *iopt, long *n, double *scale, double *x, double‐
complex *y, double *trigs, long *ifac, double *work, long
*lwork, long *ierr);
PURPOSEdfftz initializes the trigonometric weight and factor tables or com‐
putes the forward Fast Fourier Transform of a double precision 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 forward transform
W = exp(isign*i*j*k*2*pi/N)
In real-to-complex transform of length N, the (N/2+1) complex output
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.
ARGUMENTS
IOPT (input)
Integer specifying the operation to be performed:
IOPT = 0 computes the trigonometric weight table and factor
table
IOPT = -1 computes forward 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 real array whose first N elements contain
the sequence to be transformed.
Y (output)
Double complex array whose first (N/2+1) elements contain the
transform results. X and Y may be the same array starting at
the same memory location, in which case the dimension of X
must be at least 2*(N/2+1). 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 dfftz(3P)
