[gmx-developers] Precision in trajectory file

Berk Hess hess at cbr.su.se
Tue Aug 3 14:49:03 CEST 2010

David van der Spoel wrote:
> On 2010-08-03 12.34, 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!
> The precision in the trr file is the complete precision. All analysis
> programs use this. Some programs have a -dp flag to print with higher
> accuracy.
This mail was double posted. There is already a discussion on gmx-users.
So please continue the discussion there.
(only g_analyze and g_energy have -dp, there seems to be note tool that
prints the full
double precision coordinates)


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