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Re: [ESPResSo-users] cell_grid $ verlet_reuse


From: Axel Arnold
Subject: Re: [ESPResSo-users] cell_grid $ verlet_reuse
Date: Thu, 6 Jan 2011 17:56:38 +0100
User-agent: KMail/1.13.2 (Linux/2.6.32-27-generic; KDE/4.4.2; x86_64; ; )

On Tuesday 04 January 2011, Mikheil Azatov wrote:
> Hi,
> 
> I noticed my cell_grid size doesn't go above curtain size. Is there a limit
> on the number of cells or something like this ? I'm running the code on 2
> CPUs and the maximum cell_grid I get is 20 40 40. If I increase the
> simulation box size or decrease the skin parameter it stays the same...

There was a long time a limit, which was lifted only in the latest version. 
However, the limit was 512 cells, which is less than what you get, so it seems 
that for you the limit is basically infinite. To check, use "puts [setmd 
max_num_cells]", or set this variable to a high value.
 
> Also I noticed that my verlet_reuse parameter can only be 0 or 1 which is
> obviously not good for parallel computing. If I decrease my skin to like
> 0.1 then verlet_reuse is always 1.0 and if I start increasing the skin.
> the verlet _reuse starts to become 0 more and more integration steps. At
> large skin like 2 or 3, verlet_reuse is 0 every integration step. I'm a
> little bit confused here how is that possible... Shouldn't verlet_reuse
> increase when I increase the skin ?

verlet_reuse tells you how often _during the last integrate command_ the 
verlet lists where updated on average. Since you do only a single time step, 
the answer can be only 0 (if no update occured) or 1 (if an update occured), 
and the number of 0s should indeed increase. If you do the typicall 100 or 
more time steps at once, the output will be more what you expect.

Axel

> for {set i 0} { $i < 10000000 } { incr i} {
>   integrate 1
>   #setmd time [expr $i*$time_step]
>     imd positions
>      puts "verlet_reuse =  [setmd verlet_reuse] "
>      puts [setmd cell_grid]
>      if {[expr $i%$pdbstep] == 0 } {
>      incr pdbindex
>      writepsf "$name$ident/$name$ident$pdbindex.psf"
>      writepdb "$name$ident/$name$ident$pdbindex.pdb"
>      puts " i = $i "
>      puts "verlet_reuse =  [setmd verlet_reuse] "
>      }
> }


-- 
JP Dr. Axel Arnold      Tel: +49 711 685 67609
ICP, Universit├Ąt Stuttgart      Email: address@hidden
Pfaffenwaldring 27
70569 Stuttgart, Germany



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