[gmx-developers] Precision in trajectory file

Inon Sharony InonShar at TAU.ac.IL
Tue Aug 3 12:34:29 CEST 2010

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!

Inon Sharony
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