Hi again,
Just to add one information to this thread.
The difference between CPU and GPU I observed did not only stem from
rounding differences.
In my CPU simulations I had used a heatup phase and tempi was therefore
set, - I did not realize that when I posted my problem.
(I guess and hope the differences from initial velocities are much larger
than those from rounding errors.)
Oliver
2012/2/24 Ross Walker <ross.rosswalker.co.uk>
> Hi Oliver,
>
> You are not specifying tempi. Thus it defaults to 0.0. Hence there are no
> initial velocities and therefore the random number generator is not used
> (with ntt=1). Hence the value of ig will have no effect and your
> simulations
> will therefore be totally deterministic as you observe. Any differences you
> see with the CPU version are just the result of divergence caused by
> rounding differences during summation which the GPU code is not affected
> by.
>
> All the best
> Ross
>
> > -----Original Message-----
> > From: Oliver Kuhn [mailto:oak.amber.googlemail.com]
> > Sent: Friday, February 24, 2012 8:37 AM
> > To: AMBER Mailing List
> > Subject: [AMBER] same simulation using different random seeds on GPU
> >
> > Hi.
> >
> > I want to use differing initial random velocities for simulations
> > running
> > on GPU.
> > That has always been working on CPU, but on the GPU I get exactly the
> > same
> > simulation.
> >
> > For example, input 1 is:
> >
> > production simulation (NPT) - 2 ns
> > &cntrl
> > ig=1,
> > irest=0,ntx=1,
> > nstlim=1000000,dt=0.002,
> > temp0=300.0,ntt=1,tautp=1.0,
> > ntc=2,ntf=2,
> > cut=9,
> > ntpr=500,ntwx=500,ntwv=0,ntwe=500,iwrap=1,
> > ntb=2,ntp=1,pres0=1.0,taup=1.0,
> > ntr=0
> > /
> >
> > and another input has ig=41
> > giving me same simulations!?
> >
> > As I googled, I found a comment from Ross that GPU uses different
> > random
> > number generators.
> > I'm quite sure he does not mean also different syntax in using it.
> > Has anyone experienced similar problem and can help me?
> >
> > Greets,
> > Oliver
> >
> > --
> > Oliver Kuhn, Department of Bioinformatics,
> > Center for Medical Biotechnology, University of Duisburg-Essen,
> > Universitätsstr. 1-5, 45141 Essen, Germany
> > phone +49 201 183-3121, oliver.kuhn.uni-due.de
> > _______________________________________________
> > AMBER mailing list
> > AMBER.ambermd.org
> > http://lists.ambermd.org/mailman/listinfo/amber
>
>
> _______________________________________________
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>
--
Oliver Kuhn, Department of Bioinformatics,
Center for Medical Biotechnology, University of Duisburg-Essen,
Universitätsstr. 1-5, 45141 Essen, Germany
phone +49 201 183-3121, oliver.kuhn.uni-due.de
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Received on Sun Feb 26 2012 - 02:30:02 PST
