sfftc2(3P) Sun Performance Library sfftc2(3P)NAMEsfftc2 - initialize the trigonometric weight and factor tables or com‐
pute the two-dimensional forward Fast Fourier Transform of a two-dimen‐
sional real array.
SYNOPSIS
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);
PURPOSEsfftc2 initializes the trigonometric weight and factor tables or com‐
putes 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 intermedi‐
ate 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) 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
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 real 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 start‐
ing at the same memory location, 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 trigonomet‐
ric 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 rou‐
tine 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
SEE ALSO
fft
CAUTIONS
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) con‐
tains the transform results.
6 Mar 2009 sfftc2(3P)
