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Re: [lammps-users] Data communication
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Re: [lammps-users] Data communication


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Wed, 29 Nov 2017 07:14:59 -0500



On Wed, Nov 29, 2017 at 3:34 AM, Notan Tah <tahnotan@...24...> wrote:
Thanks for your reply. I want to know whether the communication via MPI is done in single precision or double precession in Molecular dynamics code.

​what do you need to know this for?

communication of data is done as 32-bit integer, 64-bit integer and double precision floating point using (64-bit) doubles as storage elements for the communication buffers.​ while encoding of 32-bit integers into doubles can be done with a typecast, doing the same for 64-bit integer requires a bit more trickery (see the ubuf struct).

​axel​

 

Thanks
Notan

On 29 November 2017 at 11:27, Andrew Jewett <jewett@...1937...> wrote:
I don't know if this answers your question, but atom positions, velocities, and forces in LAMMPS are represented using 64bit doubles.  (Check out "atom.h".  If you grep " float " *.h in the LAMMPS' "src/" directory, you'll see a few places where single precision floats are used, but that code seems to be specific for the calculation of long-range electrostatic interactions.)

Cheers
Andrew

On Tue, Nov 28, 2017 at 9:07 PM, Notan Tah <tahnotan@...24...> wrote:
Dear user,
                 I have an query about data communication in lammps.  In lammps code data communication did in single precession or double precession?
Thanks in advance for your time and consideration.

Thanks
Notan

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--
Dr. Axel Kohlmeyer  akohlmey@...12...24...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.