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Re: [ESPResSo-users] Verlet list and LB

From: Owen Hickey
Subject: Re: [ESPResSo-users] Verlet list and LB
Date: Fri, 26 Sep 2014 14:46:14 +0200

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).
> Cheers,
> Hender
> 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,
>> Owen
>> 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?
>>> Best,
>>> Hender

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