Contents
cffts - initialize the trigonometric weight and factor
tables or compute the inverse Fast Fourier Transform of a
complex sequence as follows.
SUBROUTINE CFFTS(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER IOPT, N, IFAC(*), LWORK, IERR
COMPLEX X(*)
REAL SCALE, Y(*), TRIGS(*), WORK(*)
SUBROUTINE CFFTS_64(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER*8 IOPT, N, IFAC(*), LWORK, IERR
REAL SCALE, Y(*), TRIGS(*), WORK(*)
COMPLEX X(*)
F95 INTERFACE
SUBROUTINE FFT(IOPT, N, [SCALE], X, Y, TRIGS, IFAC, WORK, [LWORK], IERR)
INTEGER*4, INTENT(IN) :: IOPT, N
INTEGER*4, INTENT(IN), OPTIONAL :: LWORK
REAL, INTENT(IN), OPTIONAL :: SCALE
COMPLEX, INTENT(IN), DIMENSION(:) :: X
REAL, 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, N
INTEGER(8), INTENT(IN), OPTIONAL :: LWORK
REAL, INTENT(IN), OPTIONAL :: SCALE
COMPLEX, INTENT(IN), DIMENSION(:) :: X
REAL, 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 cffts_ (int *iopt, int *n, float *scale, complex *x,
float *y, float *trigs, int *ifac, float *work,
int *lwork, int *ierr);
void cffts_64_ (long *iopt, long *n, float *scale, complex
*x, float *y, float *trigs, long *ifac, float
*work, long *lwork, long *ierr);
cffts initializes the trigonometric weight and factor tables
or computes the inverse Fast Fourier Transform of a 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)
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 complex array whose first (N/2+1)
elements are the input sequence to be transformed.
Y (output)
Real 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. Oth-
erwise, 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