[gmx-users] trjconv precision lost from double to single conversion

[Johnny Lu]

When I test the disk space that I would save by getting rid the water in
the trajectory, I found that only make the trajectory 1/4 as large as the
original.
The trajectory has both position and force.

Yet, the proteins only have about 1/10 the number of atoms of the whole
system.

Group     0 (         System) has 29859 elements
Group     1 (        Protein) has  2598 elements

Should the trajectory file size reduced to 1/4 instead of 1/10?

The command that I used was:
echo -e "1\n1\n" | $GMXHOME/trjconv_d -f $In_Traj -o $Out_Traj -s $In_ptr
-pbc mol -ur compact -center -force

Thanks again.

On Fri, Dec 12, 2014 at 10:31 AM, Johnny Lu <johnny.lu128 at gmail.com> wrote:
>
> Hi. I'm using gromacs 4.6.7
>
> If the trr trajectory file is from double precision calculation, and I use
> single precision trjconv to make a single precision trr trajectory, how
> much precision will I lose in position and in force?
>
> 1, 0.1, 0.01, or 0.001 angstrom and Newton?
>
> Is the lost of precision acceptable?
>
> I noticed that single precision trr seems to take about half the hard disk
> space of double precision trr.
>
> Thank you.
>