CFFT (3sciport)

Applies a Fast Fourier Transform (FFT)

SYNOPSIS

  Call CFFT( isign, n, scale, x, incx, y, incy, table, ntable, work, nwork )

ARGUMENTS

  isign           Integer.
                  Specifies whether to initialize the coefficient table,
                  perform a forward FFT, perform an inverse FFT, or activate
                  an escape mechanism. Legitimate values for isign are:

                  0  overlay table with a CXML FFT structure,
                  +1 compute a  forward transform, and
                  -1 compute an inverse transform.

                  If isign is equal to '80FF0FF0FF0FF0FF'X, then free the
                  CXML structure overlaying table.

  n               Integer.
                  The order of the FFT.

  scale           Real.
                  Each element of the complex output vector y is multipled by
                  scale after the FFT is performed.

  x               Complex vector.
                  The complex input vector to be transformed.

  incx            Integer.
                  The increment between elements of vector x.

  y               Complex vector.
                  The complex output vector. If the output vector overlays
                  the input vector, an in-place FFT is performed.

  incy            Integer.
                  The increment between elements of vector y.

  table           Real vector.
                  A vector of constants used by the FFT algorithm. The table
                  is written only when isign is zero. Only the first 121
                  locations are used by the SCIPORT implementation.

  ntable          Integer.
                  The length of the table vector. ntable must be at least
                  121.

  work            Real vector.
                  A vestigial argument ignored by the SCIPORT implementation.

  nwork           Integer.
                  A vestigial argument ignored by the SCIPORT implementation.

DESCRIPTION

  CFFT computes a Fourier Transform using the complex data vector x and the
  coefficient vector table as inputs and the complex vector y as output.

  For equations and other information, see Volume 3: UNICOS Math and
  Scientific Library Reference Manual SR-2081 7.0, Cray Research, Inc.

NOTE

  Calling CFFT with isign set to '80FF0FF0FF0FF0FF'X initiates an escape.
  Please see the sciport man page for details. The escape mechanism should be
  inserted immediately after the last call to CFFT for which the status of
  table is known. This mechanism should be used sparingly. Its use implies
  frequent re-initializations of the sine and cosine tables - which are quite
  costly.

  See also sciport.