CRFFT2 (3sciport)

Applies a complex to real Fast Fourier Transform (FFT)

SYNOPSIS

  Call CRFFT2( init, ix, n, x, work, y )

ARGUMENTS

  init            Integer
                  Initialization flag. If init is non-zero and not equal to
                  '80FF0FF0FF0FF0FF'X then work is overlaid by a CXML FFT
                  structure, which is also initialized. If init is non-zero
                  and equal to '80FF0FF0FF0FF0FF'X then the CXML FFT
                  structure overlaying work is freed. Otherwise, the CXML
                  structure overlaying work is used.

  ix              Integer
                  Direction flag. If ix > 0 then Fourier analysis is
                  performed. If ix < 0 then Fourier synthesis is performed.
                  If ix = 0 no calculations are performed.

  n               Integer
                  Size of Fourier transform; 2**n where n >= 3.

  x               Complex vector.
                  A complex input vector of n values.

  work            Complex vector.
                  A working storage vector of at least 55 complex values.

  y               Real vector.
                  A real result vector of n values.

DESCRIPTION

  The subroutine CRFFT2 calculates a Fourier synthesis if the sign of ix is
  negative and a Fourier analysis if the sign of ix is positive.

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

NOTE

  Calling CRFFT2 with init 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 CRFFT2 for which the status of
  work 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.