[gmx-users] Precision in trajectory file

Baofu Qiao qiaobf at gmail.com
Tue Aug 3 13:26:44 CEST 2010

The number of digits in .gro( or .pdb) is crudely fixed because of the
format. Otherwise, it cannot be recognized by other softwares, like VMD.

For the .trr files, I guess, if you are indeed running double-precision
GMX, the leap-frog integrator is using double-precision coordinates, but
the printed value in .trr is also truncated due to the format problem.

Inon Sharony wrote:
> Good afternoon!
> It seems to me that although I'm running a double-precision
> installation of GROMACS, the printout to file (of the positions and
> velocities) is of much less precision. i.e. the computation is done on
> numbers with something like 16 significant digits, but the last 10 of
> those are simply truncated and lost (e.g. positions are given in
> single-precision as 0.000 nm, and in double-precision as 0.00000 nm).
> Since I've already spent computation time at getting double-precision,
> I'd like to make use of all of it -- for my own reasons. I already
> searched the manuals, mailing lists and source code for instruction
> but didn't find any.
> Could you please tell me how I can change the number of digits printed
> out (e.g. to the .trr file)? I'm looking for a more elegant solution
> than adding a printf line to the source code. Something along the
> lines of changing the format of numbers in the function that prints to
> .trr .
> Thanks in advance!

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