[gmx-users] loss of precision in *.gro

[Erik Lindahl]

> 
> after energy minimization, one has two file: {*}.gro and {*}.trr. Before
> doing normal mode analysis, one should use:
> 
> grompp -v -f em -c {*}.gro -o {*}_em.tpr -p {*}.top -t {*}.trr
> 
> if you do not use  -t {*}.trr then the forces computed from  {*}.gro will
> be very large.
> 

Exactly. By reading from the trr file you maintain the full precision it 
   was written in (single or double), and you avoid the loss of 
precision from writing and reading it in ascii format.

You can actually write .gro files in any precision you want with trjconv 
(although you should start from a trr file with higher precision :-), 
and if there are more than three decimals they will be used. I'd 
definitely recommend using the trr directly though...

Cheers,

Erik