Contents
sfftc - initialize the trigonometric weight and factor
tables or compute the forward Fast Fourier Transform of a
real sequence.
SUBROUTINE SFFTC(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER IOPT, N, IFAC(*), LWORK, IERR
COMPLEX Y(*)
REAL X(*), SCALE, TRIGS(*), WORK(*)
SUBROUTINE SFFTC_64(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER*8 IOPT, N, IFAC(*), LWORK, IERR
REAL X(*), SCALE, TRIGS(*), WORK(*)
COMPLEX Y(*)
F95 INTERFACE
SUBROUTINE FFT(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, [LWORK], IERR)
INTEGER*4, INTENT(IN) :: IOPT
INTEGER*4, INTENT(IN), OPTIONAL :: N, LWORK
REAL, INTENT(IN), OPTIONAL :: SCALE
REAL, INTENT(IN), DIMENSION(:) :: X
COMPLEX, INTENT(OUT), DIMENSION(:) :: Y
REAL, INTENT(INOUT), DIMENSION(:) :: TRIGS
INTEGER*4, INTENT(INOUT), DIMENSION(:) :: IFAC
REAL, INTENT(OUT), DIMENSION(:) :: WORK
INTEGER*4, 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, INTENT(IN), OPTIONAL :: SCALE
REAL, INTENT(IN), DIMENSION(:) :: X
COMPLEX, INTENT(OUT), DIMENSION(:) :: Y
REAL, INTENT(INOUT), DIMENSION(:) :: TRIGS
INTEGER(8), INTENT(INOUT), DIMENSION(:) :: IFAC
REAL, INTENT(OUT), DIMENSION(:) :: WORK
INTEGER(8), INTENT(OUT) :: IERR
C INTERFACE
#include <sunperf.h>
void sfftc_ (int *iopt, int *n, float *scale, float *x, com-
plex *y, float *trigs, int *ifac, float *work, int
*lwork, int *ierr);
void sfftc_64_ (long *iopt, long *n, float *scale, float *x,
complex *y, float *trigs, long *ifac, float *work,
long *lwork, long *ierr);
sfftc initializes the trigonometric weight and factor tables
or computes the forward Fast Fourier Transform of a real
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)
Real scalar by which transform results are scaled.
Unchanged on exit. SCALE is defaulted to 1.0 for
F95 INTERFACE.
X (input) On entry, X is a real array whose first N elements
contain the sequence to be transformed.
Y (output)
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)
Real array of length 2*N that contains the tri-
gonometric weights. The weights are computed 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)
Real 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
fft