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Re: [lammps-users] LAMMPS: Inquiry on Random Seed and Data Reproduction"
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Re: [lammps-users] LAMMPS: Inquiry on Random Seed and Data Reproduction"


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Mon, 14 Aug 2017 04:57:17 -0400



On Mon, Aug 14, 2017 at 2:58 AM, MASATO KOIZUMI <mkoizumi@...3709...> wrote:
Dear Dr. Axel Kohlmeyer,

Hello Dr. Kohlmeyer. Thank you for your e-mail.

I was curious if my understanding is correct. 

If my input script contains a command line such as "velocity all create 1.0 1483274" and run this script many times, the random seed will ensure that I will reproduce the exact same results when I run the same script multiple times.

​why don't you just read the documentation? start here: ​http://lammps.sandia.gov/doc/Section_errors.html
 

However, if my input script has "pair_style dpd 1.0 1.0 1224589" or any other command such as "fix langevin" that has a thermal input argument, there is no guarantee that I will reproduce the exact same results for every same run due to the inevitable "thermal noise."

Furthermore, if I have dpd pairwise command where the pairwise coefficient frequently changes for every 50 timesteps like the example below, the random seed will not be able to reproduce same results.

pair_style dpd 1.0 1.0 122347

pair_coeff * * 25 4.5 1.0

run 1000

pair_coeff * * 50.0 4.5 1.0

velocity all create 1.0 15086120

run 50

pair_coeff * * 100.0 4.5 1.0

velocity all create 1.0 15786120

run 50

pair_coeff * * 150.0 4.5 1.0

velocity all create 1.0 15486120

run 50


Overall, I was curious if you suggest that these slight variations in data reproduction should not be an issue since the deviation is marginal.

​go and pick up a text book on statistical thermodynamics​ and learn why.

as i have been pointing out before. this *exact* same issue has been discussed multiple times on this mailing list. in some cases at great length.
go and study those discussions properly and your questions will be answered.

axel.

 

Thank you.

Sincerely,

Masato Koizumi


​--​

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