[gmx-developers] [RFE] Converting velocities / parsing with trjconv

[Berk Hess]

>From: Jay Mashl <mashl at uiuc.edu>
>To: gmx-developers <gmx-developers at gromacs.org>
>CC: Jay Mashl <mashl at uiuc.edu>
>Subject: [gmx-developers] [RFE] Converting velocities / parsing with 
>trjconv
>Date: Mon, 3 Jun 2002 12:39:18 -0500 (CDT)
>
>
>I have been looking for a way to generate velocity trajectories and ran 
>into
>some difficulties with trjconv. When nstvout > nstxout, there is a trivial 
>hack
>to do this.
>
>However, if the velocities have been saved more often than the coordinates
>(i.e., nstvout < nstxout), then the default trjconv semes to overlook those
>frames without a leading set of coordinates. Glancing at the source, it 
>could
>be that the velocities are read as coordinates instead.
>
>What are your thoughts on providing a sort of "-nogro" option in trjconv?  
>It
>might be nice to be able to split coordinate, velocity, and force 
>trajectories
>into separate files, regardless of the values for nstvout, nstxout, 
>nstfout.
>

For trr/trj output trjconv reads all frames, including those with only 
velocities
or only forces.
The problem is probably that you requested the wrong output type (xtc or 
gro?),
which requires coordinates in every frame.

I don't see any real advantage of having a trajectory with only velocities 
or
forces. Having coordinates as well doubles the size of the file, which 
should
not be a problem in the rare cases that one only needs velocities or forces.

Berk.



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