g_filter VERSION 3.3_beta_20050823

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 file.

-f traj.xtc Input Generic trajectory: xtc trr trj gro g96 pdb

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

-n index.ndx Input, Opt. Index file

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

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

-[no]h no 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)

-[no]w no View output xvg, xpm, eps and pdb files

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

-[no]all no Write all low-pass filtered frames

-[no]nojump yes Remove jumps of atoms across the box

-[no]fit no Fit all frames to a reference structure

gromacs(7)

More information about the GROMACS suite is available in /usr/share/doc/gromacs or at <http://www.gromacs.org/>.