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

[Mark Abraham]

On Fri, Dec 12, 2014 at 4:31 PM, 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?
>

You'll go from practically infinite precision for any such quantity to
about 6 significant figures, ie. double floating-point precision to single.
Their representations are kind of like scientific notation. Read up on
wikipedia about those :-)

1, 0.1, 0.01, or 0.001 angstrom and Newton?
>

That depends on the magnitude of the numbers. You're getting a change in
relative precision.

Is the lost of precision acceptable?
>

Depends what you're using them for.


> I noticed that single precision trr seems to take about half the hard disk
> space of double precision trr.
>

Yep.

Mark


>
> Thank you.
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