Contents
dfftz - initialize the trigonometric weight and factor
tables or compute the forward Fast Fourier Transform of a
double precision sequence.
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, doublecomplex *y, double *trigs, long *ifac,
double *work, long *lwork, long *ierr);
dfftz initializes the trigonometric weight and factor tables
or computes 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) com-
plex 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.
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 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