[gmx-users] Precision in trajectory file

[Baofu Qiao]

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!
>