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Re: [ESPResSo-users] Simulation of fluid using LB-method

From: Olaf Lenz
Subject: Re: [ESPResSo-users] Simulation of fluid using LB-method
Date: Mon, 27 Jan 2014 15:04:49 +0100

Maybe you can also send your config.log? Then we can see how the program is compiled.


2014-01-27 Georg Rempfer <address@hidden>
Hello Markus,

the friction parameter won't have an influence on your simulation as long as you don't use any explicit particles. Can you provide your simulation script? If you give it to me, I will run and time it here.


2014-01-27 Ulf Schiller <address@hidden>

On 01/27/2014 02:07 PM, Wink, Markus wrote:

I hope I understood your point correctly. I have run the script with two calls of "integrate 1000", having a box of 50^3 and an agrid of 1, resulting in 125*10^6 site updates.
It took 22 min 2s for the simulation resulting in roughly 19k SUPS. This is far below your expected 10M. I have no clue what the reason for that is.

The binary of Espresso I have created only had "LB", "LB_BOUNDARIES" and "EXTERNAL_FORCES" activated.  Running the testscript "lb_planar.tcl" (box of length 12, total integrate of 5000) takes about 14 sec, resulting in ~0.6M SUPS.


well, Espresso has of course some overhead since it's not a pure LB code, but ~200k (that's what you get I think) resp. 600k seems pretty slow. What CPU are you running on?

Does anyone else have an estimate of how many site updates per second they get?


-----Ursprüngliche Nachricht-----
Von: [mailto:espressomd-users-bounces+markus.wink=imm.address@hidden] Im Auftrag von Ulf Schiller
Gesendet: Montag, 27. Januar 2014 12:16
An: address@hidden
Betreff: Re: [ESPResSo-users] Simulation of fluid using LB-method

On 01/27/2014 11:54 AM, Wink, Markus wrote:
3) Even though, the velocity profile saturates, it takes pretty long
(time scale of days). The saturation sets in at about 350 times the
"integration 1000" command. This corresponds to a time scale of ms in Si
units. Besides using OpenMpi or the GPU impementation, is there anyway
to speeden up the simulation? For example by adjusting the parameter tau
in the lbfluid command?


that sounds a bit strange to me. If your system is 50^3 and you
integrate 1000 steps, that gives 125*10^6 site updates. On a reasonably
modern CPU, a reasonable LB code should get to around 10M SUPS (million
site updates per second), that is, one call of "integrate 1000" should
not take much more than 10 seconds, so 350 calls roughly one hour not
days. Can you check how many site updates per second you get on your system?


Dr. Ulf D. Schiller                        Building 04.16, Room 3006
Institute of Complex Systems (ICS-2)       Phone:   +49 2461 61-6144
Forschungszentrum Jülich, Germany          Fax:     +49 2461 61-3180

Dr. rer. nat. Olaf Lenz
Institut für Computerphysik, Allmandring 3, D-70569 Stuttgart
Phone: +49-711-685-63607

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