Contents
sfftc2 - initialize the trigonometric weight and factor
tables or compute the two-dimensional forward Fast Fourier
Transform of a two-dimensional real array.
SUBROUTINE SFFTC2(IOPT, N1, N2, SCALE, X, LDX, Y, LDY, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER IOPT, N1, N2, LDX, LDY, IFAC(*), LWORK, IERR
COMPLEX Y(LDY, *)
REAL X(LDX, *), SCALE, TRIGS(*), WORK(*)
SUBROUTINE SFFTC2_64(IOPT, N1, N2, SCALE, X, LDX, Y, LDY, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER*8 IOPT, N1, N2, LDX, LDY, IFAC(*), LWORK, IERR
REAL X(LDX, *), SCALE, TRIGS(*), WORK(*)
COMPLEX Y(LDY, *)
F95 INTERFACE
SUBROUTINE FFT2(IOPT, [N1], [N2], [SCALE], X, [LDX], Y, [LDY], TRIGS,
& IFAC, WORK, [LWORK], IERR)
INTEGER*4, INTENT(IN) :: IOPT
INTEGER*4, INTENT(IN), OPTIONAL :: N1, N2, LDX, LDY, 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 FFT2_64(IOPT, [N1], [N2], [SCALE], X, [LDX], Y, [LDY], TRIGS, IFAC, WORK, [LWORK], IERR)
INTEGER(8), INTENT(IN) :: IOPT
INTEGER(8), INTENT(IN), OPTIONAL :: N1, N2, LDX, LDY, 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 sfftc2_ (int *iopt, int *n1, int *n2, float *scale,
float *x, int *ldx, complex *y, int *ldy, float
*trigs, int *ifac, float *work, int *lwork, int
*ierr);
void sfftc2_64_ (long *iopt, long *n1, long *n2, float
*scale, float *x, long *ldx, complex *y, long
*ldy, float *trigs, long *ifac, float *work, long
*lwork, long *ierr);
sfftc2 initializes the trigonometric weight and factor
tables or computes the two-dimensional forward Fast Fourier
Transform of a two-dimensional real array. In computing the
two-dimensional FFT, one-dimensional FFTs are computed along
the columns of the input array. One-dimensional FFTs are
then computed along the rows of the intermediate results.
N2-1 N1-1
Y(k1,k2) = scale * SUM SUM W2*W1*X(j1,j2)
j2=0 j1=0
where
k1 ranges from 0 to N1-1 and k2 ranges from 0 to N2-1
i = sqrt(-1)
isign = -1 for forward transform
W1 = exp(isign*i*j1*k1*2*pi/N1)
W2 = exp(isign*i*j2*k2*2*pi/N2)
In real-to-complex transform of length N1, the (N1/2+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
N1 (input)
Integer specifying length of the transform in the
first dimension. N1 is most efficient when it is
a product of small primes. N1 >= 0. Unchanged on
exit.
N2 (input)
Integer specifying length of the transform in the
second dimension. N2 is most efficient when it is
a product of small primes N2 >= 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) X is a complex array of dimensions (LDX, N2) that
contains input data to be transformed. X and Y
can be the same array.
LDX (input)
Leading dimension of X. LDX >= N1 if X is not the
same array as Y. Else, LDX = 2*LDY. Unchanged on
exit.
Y (output)
Y is a complex array of dimensions (LDY, N2) that
contains the transform results. X and Y can be
the same array starting at the same memory loca-
tion, in which case the input data are overwritten
by their transform results. Otherwise, it is
assumed that there is no overlap between X and Y
in memory.
LDY (input)
Leading dimension of Y. LDY >= N1/2+1 Unchanged
on exit.
TRIGS (input/output)
Real array of length 2*(N1+N2) that contains the
trigonometric 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 2*128 that
contains the factors of N1 and N2. The factors
are computed when the routine is called with IOPT
= 0 and they are used in subsequent calls when
IOPT = -1. Unchanged on exit.
WORK (workspace)
Real array of dimension at least MAX(N1,
2*N2)*NCPUS, where NCPUS is the number of threads
used to execute the routine. 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 = N1 < 0
-3 = N2 < 0
-4 = (LDX < N1) or (LDX not equal 2*LDY when X and
Y are same array)
-5 = (LDY < N1/2+1)
-6 = (LWORK not equal 0) and (LWORK <
MAX(N1,2*N2)*NCPUS)
-7 = memory allocation failed
fft
Y(N1/2+1:LDY,:) is used as scratch space. Upon returning,
the original contents of Y(N1/2+1:LDY,:) will be lost,
whereas Y(1:N1/2+1,1:N2) contains the transform results.