[gmx-users] RE: programmes to have in double precision besides mdrun_d

[Alan]

Thank you guys

Indeed, it's better have all programmes in double version anyway.

But now, I may be dreaming, but how 'impossible' is to have one single
binary able to work with single or double precision with a simple
input option or env variable? At least on Mac one can have more than
one binary (for different archs) in 'single' file. And yes, a wrapping
script could address that but it's not what I have in mind anyway.

Cheers,
Alan

On Wed, Jun 17, 2009 at 15:16, <gmx-users-request at gromacs.org> wrote:
>> Jussi Lehtola skrev:
>> > On Wed, 2009-06-17 at 13:45 +0200, Berk Hess wrote:
>> >
>> >> Hi,
>> >>
>> >> Nothing needs to be double precision.
>> >>
>> >> Why do you want mdrun in double precision?
>> >> The only common reason for this is normal mode analysis,
>> >> in which case you need all the tools involved in double precision.
>> >> For normal MD simulation there is nearly never a need for
>> >> double precision.
>> >>
>> >
>> > If you want to run accurate NVE simulations, double precision is
>> > important. If you use thermostats, then there is no need for double
>> > precision.
>> >
>> >
>> I can testify to that. Without double precision I've had problems with
>> drifting total energy when doing non-periodic NVE.
>>
>
> Indeed, this is correct.
> But I guess this falls into the category nearly never.
> On the other hand, there are so many Gromacs users nowadays,
> there nearly never is nearly never zero users.
>
>> /Erik
>> > Also, I have found that double precision can be nice for energy
>> > minimization since it can handle more pathological cases than single
>> > precision. Still, usually it doesn't matter much whether the starting
>> > point was prepared in single or double precision.
>> >
>
>
> That's true.
> It would be nice if we could make the single precision code
> handle such cases better (force capping?).
>
> Berk
>

-- 
Alan Wilter S. da Silva, D.Sc. - CCPN Research Associate
Department of Biochemistry, University of Cambridge.
80 Tennis Court Road, Cambridge CB2 1GA, UK.
>>http://www.bio.cam.ac.uk/~awd28<<