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Re: [ESPResSo-users] Verlet list and LB

From: Axel Arnold
Subject: Re: [ESPResSo-users] Verlet list and LB
Date: Mon, 29 Sep 2014 16:21:29 +0200
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

Just as a remark: it is quite likely that larger skins give better performance if your system is rather dilute, which is often the case when using LB. Then you avoid some communication without actually having the burden of computing much more interactions.


On 26.09.14 14:46, Owen Hickey wrote:
Hey Hender,

Well since the skin doesn't change anything other than the
performance, pick whichever gives the fastest results!


On Fri, Sep 26, 2014 at 2:41 PM, Hender Lopez <address@hidden> wrote:
Hi Owen,

Thanks again for your quick reply. Yes your are right with the typical
parameters for the grid size and the skin, but I was just playing
around and notice that for a particular simulation if I had both
parameter of around the same size the speed of the calculation
increased substantially and the physics seems to be OK (I am still
checking this).



On Fri, Sep 26, 2014 at 1:09 PM, Owen Hickey <address@hidden> wrote:
Hey Hender,

Yes, the GPU version is able to handle skins greater than half the
grid size. The reason for this is that currently the GPU only works on
a single GPU and thus their are no ghost particles (this may change in
the future). The CPU version is made for multiple processors and
particles on the edge of two domains need to be on both nodes. This is
done through the use of ghost particles on one of the nodes. This is
only possible if the skin is less than half the grid size. I am a bit
curious about your parameters. Typically one would set the grid size
to 1 and the skin to 0.3 which would work with both versions.

Kind regards,

On Fri, Sep 26, 2014 at 2:02 PM, Hender Lopez <address@hidden> wrote:
Dear all,

I am running some sims with a LB thermostat and if I use the CPU
version (espresso-3.2.0 and espresso-3.3.0) I get the following error:

background_errors 0 {104 LB requires either no Verlet lists or that
the skin of the verlet list to be less than half of lattice-Boltzmann
grid spacing.}

Now if I use a skin greater that half of lattice-Boltzmann grid
spacing with the GPU LB version the programs runs without any problem
(again for both versions of espresso). My question is: is this OK , is
the GPU version able to handle a skin greater that half of
lattice-Boltzmann grid?



JP Dr. Axel Arnold
ICP, Universit├Ąt Stuttgart
Allmandring 3
70569 Stuttgart, Germany
Email: address@hidden
Tel: +49 711 685 67609

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