NAME

     freqtim  - inverse fast fourier transform

SYNOPSIS

     freqtim [ -Nntap ] [ -Ootap ] [ -rrot ] [ -P ] [ -RI ] [  -M
     ] [ -V ] [ -? ]

DESCRIPTION

     freqtim implements the MathAdvantage inverse FFT by applying
     it to the data from timfreq and outputs the data in USP for-
     mat.  The default is to assume input trace pairs composed of
     amplitude transform values and phase (degrees) values alter-
     nating throughout the data.  The output data  will  be  real
     and will have 1/2 the number traces per record as the input.
     Optionally the input may consist of amplitude and phase  (in
     degrees)  packed into a single trace  where the amplitude is
     in the top half of the trace (with Nyquist at sample 1)  and
     where  the  phase  is  in the bottom half of the trace (with
     Nyquist at the last sample).

     freqtim gets its global parameters from command  line  argu-
     ments.   These arguments specify the input, output, and ver-
     bose printout, if desired.

  Command line arguments
     -N ntap
          Enter the input data set name or file immediately after
          typing -N unless the input is from a pipe in which case
          the -N entry must be omitted.  This input  file  should
          include the complete path name if the file resides in a
          different directory.  Example -N/b/vsp/dummy tells  the
          program to look for file 'dummy' in directory '/b/vsp'.

     -O otap
          Enter the output data  set  name  or  file  immediately
          after typing -O.  This output file is not required when
          piping the output to another process.  The output  data
          set also requires the full path name (see above).

     -r rot
          Enter the phase rotation in degrees (def = 0).

     -RI  Enter the command line argument '-RI'  to  output  real
          and  imaginaries  (default  is  to output amplitude and
          phase in degrees.

     -M   Enter the command line argument '-M' to restore a  mute
          based on the times found in trace header word VPick1.

     -P   Enter the command  line  argument  '-P'  to  cause  the
          amplitude and phase valuess to be packed into each out-
          put trace. The top half of the trace will  contain  the
          amplitudes with Nyquist starting at sample 1 and count-
          ing down to DC at the middle sample.  The  bottom  half
          will  contain  the  phase  with DC at the middle sample
          plus 1 counting up to Nyquist at the last sample.  With
          this  option  there  will  be the same number of output
          traces/rec as the input.  If this option is to be  used
          in the freqtim command line you must use it here.

     -V   Enter the command line argument '-V' to get  additional
          printout.

     -?   Enter the command line  argument  '-?'  to  get  online
          help.   The program terminates after the help screen is
          printed.

BUGS

     You must tell this program explicitly  whether  or  not  the
     amplitude  and  phase  are packed into trace pairs or into a
     single trace ( -P ).

SEE ALSO

     freqtim

AUTHOR

     Paul Gutowski, x3146, TRC

COPYRIGHT

     copyright 2001, Amoco Production Company
               All Rights Reserved
          an affiliate of BP America Inc.