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       g_velacc - calculates velocity autocorrelation functions

       VERSION 4.0.1


       g_velacc  -f traj.trr -s topol.tpr -n index.ndx -o vac.xvg -[no]h -nice
       int -b time -e time -dt time -[no]w -[no]xvgr -[no]m  -[no]mol  -acflen
       int  -[no]normalize  -P  enum  -fitfn  enum  -ncskip int -beginfit real
       -endfit real


       g_velacc computes the velocity autocorrelation function.  When the   -m
       option is used, the momentum autocorrelation function is calculated.

       With option  -mol the velocity autocorrelation function of molecules is
       calculated. In this case the index group  should  consist  of  molecule
       numbers instead of atom numbers.


       -f traj.trr Input
        Full precision trajectory: trr trj cpt

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

       -n index.ndx Input, Opt.
        Index file

       -o vac.xvg Output
        xvgr/xmgr file


        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

        Add  specific  codes  (legends  etc.)  in the output xvg files for the
       xmgrace program

        Calculate the momentum autocorrelation function

        Calculate the velocity acf of molecules

       -acflen int -1
        Length of the ACF, default is half the number of frames

        Normalize ACF

       -P enum 0
        Order of Legendre polynomial for ACF (0 indicates none):  0,  1,  2 or

       -fitfn enum none
        Fit  function:   none,   exp,   aexp,   exp_exp,  vac,  exp5,  exp7 or

       -ncskip int 0
        Skip N points in the output file of correlation functions

       -beginfit real 0
        Time where to begin the exponential fit of the correlation function

       -endfit real -1
        Time where to end the exponential fit of the correlation function,  -1
       is till the end



       More      information     about     GROMACS     is     available     at

                                Thu 16 Oct 2008                    g_velacc(1)