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Updated: June 2017
 
 

cffts (3p)

Name

cffts - pute the inverse Fast Fourier Transform of a complex sequence as fol- lows.

Synopsis

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);

Description

Oracle Solaris Studio Performance Library                            cffts(3P)



NAME
       cffts  -  initialize the trigonometric weight and factor tables or com-
       pute the inverse Fast Fourier Transform of a complex sequence  as  fol-
       lows.

SYNOPSIS
       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);



PURPOSE
       cffts  initializes  the  trigonometric weight and factor tables or com-
       putes the inverse Fast Fourier Transform of a complex sequence as  fol-
       lows:

                      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) complex 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.


ARGUMENTS
       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.


       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 trans-
                 form results.  X and Y may be the same array starting at  the
                 same memory location.  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  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 128 that contains 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

SEE ALSO
       fft



                                  7 Nov 2015                         cffts(3P)