[gmx-developers] (no subject)

[Oliver Lange]

Hi,

thank you for the bug-report. 

This bug is new. It did not exist in Gromacs 3.2.1.
As a work-around, just remove the offending line as long as you don't 
use edsampling
** bHaveConstr = bHaveConstr || ed_constraints(edyn);  **

The problem exists, because edsam is not really implemented with 
parallelism in mind. Thus, the slaves do not no if edsampling is 
switched on or not.
I will implement a MPI -communication step to amend this in the 
initialization step, and upload this to CVS.

Oliver

H.J.Risselada wrote:

>
> Dear gmx-developers,
>
> I discovered a bug in GROMACS-3.3 in mdlib/update.c concerning the 
> usage of constraints.
>
> I discovered that the temperature on the slaves during a parallel run 
> was 30 K lower at ref_t 300 K then on the master at all times.
>
> I used a LJ-particles only test system without constaints:
>
> Constaints where put on "none" in the mdp file.
>
> However,
>
>  /* if edyn->bEdsam == FALSE --- this has no effect */
>     bHaveConstr = bHaveConstr || ed_constraints(edyn);
>
> returns FALSE on the master, but TRUE on the slaves.
>
> This means that the constrainst loops become active on the slaves, 
> which will interfere with the dynamics.
>
> When T-coupling is used, one temperature group can be both devided on 
> the master as on the slaves. The total mean temperature of the T-group 
> will be the desired temperature.
> However the desired maxwell distribution will be disrupted.
>
> This Bug may have a significant effect on the users of GC-models.
>
> I tested it for the version 3.3, but it may also be present in the 
> older versions.
>
> greetings
>
> Jelger.
>
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>

-- 
Oliver Lange
MPI for biophysical Chemistry
olange at gwdg.de
Fax: +495512012302
Tel: +495512012305