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       g_filter  -  frequency  filters  trajectories, useful for making smooth

       VERSION 4.0.1


       g_filter -f traj.xtc -s topol.tpr  -n  index.ndx  -ol  lowpass.xtc  -oh
       highpass.xtc  -[no]h  -nice int -b time -e time -dt time -[no]w -nf int
       -[no]all -[no]nojump -[no]fit


       g_filter performs frequency filtering  on  a  trajectory.   The  filter
       shape  is cos(pi t/A) + 1 from -A to +A, where A is given by the option
       -nf times the time step in the input trajectory.  This  filter  reduces
       fluctuations  with  period  A  by  85%, with period 2*A by 50% and with
       period 3*A  by  17%  for  low-pass  filtering.   Both  a  low-pass  and
       high-pass filtered trajectory can be written.

       Option   -ol writes a low-pass filtered trajectory.  A frame is written
       every  nf input  frames.   This  ratio  of  filter  length  and  output
       interval  ensures  a  good  suppression  of  aliasing of high-frequency
       motion, which is useful for making  smooth  movies.  Also  averages  of
       properties which are linear in the coordinates are preserved, since all
       input frames are weighted equally in the output.  When all  frames  are
       needed, use the  -all option.

       Option   -oh  writes  a  high-pass  filtered trajectory.  The high-pass
       filtered coordinates are added to the coordinates  from  the  structure
       file.  When  using high-pass filtering use  -fit or make sure you use a
       trajectory which has been fitted on the coordinates  in  the  structure


       -f traj.xtc Input
        Trajectory: xtc trr trj gro g96 pdb cpt

       -s topol.tpr Input, Opt.
        Structure+mass(db): tpr tpb tpa gro g96 pdb

       -n index.ndx Input, Opt.
        Index file

       -ol lowpass.xtc Output, Opt.
        Trajectory: xtc trr trj gro g96 pdb

       -oh highpass.xtc Output, Opt.
        Trajectory: xtc trr trj gro g96 pdb


        Print help info and quit

       -nice int 19
        Set the nicelevel

       -b time 0
        First frame (ps) to read from trajectory

       -e time 0
        Last frame (ps) to read from trajectory

       -dt time 0
        Only use frame when t MOD dt = first time (ps)

        View output xvg, xpm, eps and pdb files

       -nf int 10
        Sets  the  filter  length  as well as the output interval for low-pass

        Write all low-pass filtered frames

        Remove jumps of atoms across the box

        Fit all frames to a reference structure



       More     information     about     GROMACS     is     available      at

                                Thu 16 Oct 2008                    g_filter(1)