1g_filter(1)               GROMACS suite, VERSION 4.5               g_filter(1)
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NAME

6       g_filter  -  frequency  filters  trajectories, useful for making smooth
7       movies
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9       VERSION 4.5
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SYNOPSIS

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

17       g_filter performs frequency filtering  on  a  trajectory.   The  filter
18       shape  is cos(pi t/A) + 1 from -A to +A, where A is given by the option
19       -nf times the time step in the input trajectory.  This  filter  reduces
20       fluctuations  with  period  A  by  85%, with period 2*A by 50% and with
21       period 3*A  by  17%  for  low-pass  filtering.   Both  a  low-pass  and
22       high-pass filtered trajectory can be written.
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25       Option   -ol writes a low-pass filtered trajectory.  A frame is written
26       every  nf input frames.  This ratio of filter length and output  inter‐
27       val  ensures  a  good suppression of aliasing of high-frequency motion,
28       which is useful for making smooth movies. Also averages  of  properties
29       which  are  linear  in  the  coordinates are preserved, since all input
30       frames are weighted equally in the output.  When all frames are needed,
31       use the  -all option.
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34       Option  -oh writes a high-pass filtered trajectory.  The high-pass fil‐
35       tered coordinates are added to the coordinates from the structure file.
36       When using high-pass filtering use  -fit or make sure you use a trajec‐
37       tory which has been fitted on the coordinates in the structure file.
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FILES

40       -f traj.xtc Input
41        Trajectory: xtc trr trj gro g96 pdb cpt
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43       -s topol.tpr Input, Opt.
44        Structure+mass(db): tpr tpb tpa gro g96 pdb
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46       -n index.ndx Input, Opt.
47        Index file
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49       -ol lowpass.xtc Output, Opt.
50        Trajectory: xtc trr trj gro g96 pdb
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52       -oh highpass.xtc Output, Opt.
53        Trajectory: xtc trr trj gro g96 pdb
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OTHER OPTIONS

57       -[no]hno
58        Print help info and quit
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60       -[no]versionno
61        Print version info and quit
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63       -nice int 19
64        Set the nicelevel
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66       -b time 0
67        First frame (ps) to read from trajectory
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69       -e time 0
70        Last frame (ps) to read from trajectory
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72       -dt time 0
73        Only use frame when t MOD dt = first time (ps)
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75       -[no]wno
76        View output xvg, xpm, eps and pdb files
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78       -nf int 10
79        Sets the filter length as well as the  output  interval  for  low-pass
80       filtering
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82       -[no]allno
83        Write all low-pass filtered frames
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85       -[no]nojumpyes
86        Remove jumps of atoms across the box
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88       -[no]fitno
89        Fit all frames to a reference structure
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SEE ALSO

93       gromacs(7)
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95       More   information  about  GROMACS  is  available  at  <http://www.gro‐
96       macs.org/>.
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100                                Thu 26 Aug 2010                    g_filter(1)