RFFTMLT (3sciport)

Applies complex to real or real to complex Fast Fourier Transforms (FFTs) on multiple input vectors

SYNOPSIS

  Call RFFTMLT( x, work, trigs ,ifax, inc1x, inc2x, n, lot, isign )

ARGUMENTS

  x               Real matrix.
                  An input/output matrix containing lot real/complex vectors
                  on input and lot complex/real vectors on output. Output
                  vectors overwrite input vectors.

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

  trigs           Real vector.
                  A vector overlaid by the CXML FFT structure. The trigs
                  vector must contain at least 105 elements. Before being
                  used, trigs must be initialized by the following call:

                  CALL FFTFAX( n,ifax,trigs ).

                  When FFTFAX is called with ifax equal to
                  '80FF0FF0FF0FF0FF'X, the FFT structure overlaying trigs is
                  freed.

  ifax            Integer vector.
                  A vestigial argument ignored by the SCIPORT implementation.

  inc1x           Integer.
                  The increment between elements within each length n data
                  vector of matrix x.

  inc2x           Integer.
                  The increment between starting elements of vectors within
                  matrix x.

  n               Integer.
                  The length of the data vectors. The value n is the length
                  of the real data vectors regardless of transform direction.

  lot             Integer.
                  The number of data vectors.

  isign           Integer.
                  +1 for a complex to real FFT
                  -1 for a real to complex FFT

DESCRIPTION

  When isign = -1, RFFTMLT applies a real to complex FFT to lot real data
  vectors, each of length n, simultaneously. When isign = +1, RFFTMLT applies
  a complex to real FFT to lot complex data vectors, each of length n/2+1,
  simultaneously.

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

NOTE

  Before RFFTMLT is called the first time, the trigs vector must be
  initialized by calling FFTFAX as shown below:

          Call FFTFAX( n,ifax,trigs )

  Thereafter, the vector trigs must not be written to. However, it can be
  used by RFFTMLT any number of times, as long as the length n is not
  changed.

  Calling FFTFAX with ifax 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 RFFTMLT for which the status of
  trigs 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.