[gmx-users] changing the velocity in trajectory file

Bogdan Costescu bcostescu at gmail.com
Mon Nov 29 20:56:17 CET 2010

On Mon, Nov 29, 2010 at 16:16, sreelakshmi ramesh
<sree.lakshmi at research.iiit.ac.in> wrote:
> so can anybody tell me how to hack the trr file so that i can change the
> velocity parameter in it

You can use the xdrfile library to read in a certain frame of the trr
file, change the velocity in the array that you get, then use the
xdrfile library again to write the trr file. It's up to you if you
recreate only the one frame in the trr file or you copy all frames
except for the one that you want to change... That's not so much about
"hacking the trr file" as it is about using the library created for
this purpose.

But this is useful only when you know what velocities you want to
generate. Are you not satisfied with the quality of the random
velocities generated by GROMACS ? Or do you want to get a particular
set of velocities that can't be generated by GROMACS ?

Good luck,

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