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Re: [ESPResSo-users] Warning Message in LB
From: |
Axel Arnold |
Subject: |
Re: [ESPResSo-users] Warning Message in LB |
Date: |
Thu, 05 Jun 2014 23:33:09 +0200 |
User-agent: |
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 |
Dear Mohamed,
please use our mailing list for Espresso related questions.
On 05.06.14 15:23, s1mokhal wrote:
Dear Mr Arnold,
My name is Mohamed Abdelkhalek, currently working on a bachelor thesis
project in Bayreuth University involving forking a version of the
latest espresso code and adding a few things for red blood cell
simulations in lb fluid. Anyway, I am having trouble understanding
this warning
"Recalculating forces, so the LB coupling forces are not included in
the particle force the first time step. This only matters if it
happens frequently during sampling."
As it keeps appearing repeatedly in my simulations which eventually
break down. So, I hoped if you can explain the exact meaning of the
warning and it's consequences ? for example when using multiple
processors I see the warning all the time.
The message says that the recalc_forces flag has been set by some
algorithm due to changes that you made between two the integrate
commands. That can be anything from changing interactions to changing
particles. If you do two integrate commands one after the other without
any other command inbetween, this should not happen, apart from your own
modifications.
As the warning says, there will be no particle coupling forces for the
first (half) time step, that is, particles will not feel the fluid. This
disturbs the LB quite a bit, and you should not use results obtained
with this message appearing regularly.
If you are sure that there is no need to recalculate forces, then you
can use the "reuse_forces" option of the integrate command, which I
added recently, and enforces reuse. But that of course means that any
changes to interactions or particles do _not_ apply for the first half
time step.
Finally, if you are only embedding blood cells, there is no need to
worry, as the blood cell marker particles are propaged differently. Just
if you also embed conventional particles, you are in trouble.
Best,
Axel
--
JP Dr. Axel Arnold
ICP, Universität Stuttgart
Allmandring 3
70569 Stuttgart, Germany
Email: address@hidden
Tel: +49 711 685 67609
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