• NAME
• F95 INTERFACE
• C INTERFACE
• PURPOSE
• ARGUMENTS
• SEE ALSO

NAME

sfftcm - initialize the trigonometric weight and factor tables or compute the one-dimensional forward Fast Fourier Transform of a set of real data sequences stored in a two-dimensional array. =head1 SYNOPSIS

  SUBROUTINE SFFTCM( IOPT, N1, N2, SCALE, X, LDX, Y, LDY, TRIGS, IFAC, 
 *      WORK, LWORK, IERR)
  COMPLEX Y(LDY,*)
  INTEGER IOPT, N1, N2, LDX, LDY, LWORK, IERR
  INTEGER IFAC(*)
  REAL SCALE
  REAL X(LDX,*), TRIGS(*), WORK(*)

  SUBROUTINE SFFTCM_64( IOPT, N1, N2, SCALE, X, LDX, Y, LDY, TRIGS, 
 *      IFAC, WORK, LWORK, IERR)
  COMPLEX Y(LDY,*)
  INTEGER*8 IOPT, N1, N2, LDX, LDY, LWORK, IERR
  INTEGER*8 IFAC(*)
  REAL SCALE
  REAL X(LDX,*), TRIGS(*), WORK(*)

F95 INTERFACE

  SUBROUTINE FFTM( IOPT, [N1], [N2], [SCALE], X, [LDX], Y, [LDY], 
 *       TRIGS, IFAC, WORK, [LWORK], IERR)
  COMPLEX, DIMENSION(:,:) :: Y
  INTEGER :: IOPT, N1, N2, LDX, LDY, LWORK, IERR
  INTEGER, DIMENSION(:) :: IFAC
  REAL :: SCALE
  REAL, DIMENSION(:) :: TRIGS, WORK
  REAL, DIMENSION(:,:) :: X

  SUBROUTINE FFTM_64( IOPT, [N1], [N2], [SCALE], X, [LDX], Y, [LDY], 
 *       TRIGS, IFAC, WORK, [LWORK], IERR)
  COMPLEX, DIMENSION(:,:) :: Y
  INTEGER(8) :: IOPT, N1, N2, LDX, LDY, LWORK, IERR
  INTEGER(8), DIMENSION(:) :: IFAC
  REAL :: SCALE
  REAL, DIMENSION(:) :: TRIGS, WORK
  REAL, DIMENSION(:,:) :: X

C INTERFACE

#include <sunperf.h>

void sfftcm(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 sfftcm_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);

PURPOSE

sfftcm initializes the trigonometric weight and factor tables or computes the one-dimensional forward Fast Fourier Transform of a set of real data sequences stored in a two-dimensional array: .Ve

                 N1-1

Y(k,l) = scale * SUM W*X(j,l)

                 j=0
.Ve

where

k ranges from 0 to N1-1 and l ranges from 0 to N2-1

i = sqrt(-1)

isign = -1 for forward transform

W = exp(isign*i*j*k*2*pi/N1)

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 input sequences. N1 is most efficient when it is a product of small primes. N1 > = 0. Unchanged on exit.

• N2 (input)
  Integer specifying number of input sequences. N2 > = 0. Unchanged on exit.

• SCALE (input)
  Real scalar by which transform results are scaled. Unchanged on exit.

• X (input)
  X is a real array of dimensions (LDX, N2) that contains the sequences to be transformed stored in its columns.

• LDX (input)
  Leading dimension of X. If X and Y are the same array, LDX = 2*LDY Else LDX > = N1 Unchanged on exit.

• Y (output)
  Y is a complex array of dimensions (LDY, N2) that contains the transform results of the input sequences. X and Y can be the same array starting at the same memory location, in which case the input sequences 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 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 N1. 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 (output)
  Real array of dimension at least N1. 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)

  -4 = (LDY < N1/2 + 1)

  -6 = (LWORK not equal 0) and (LWORK < N1)

  -7 = memory allocation failed

SEE ALSO

fft