**From:** Himanshu Khandelia (*hkhandel_at_memphys.sdu.dk*)

**Date:** Thu Nov 22 2007 - 02:19:55 CST

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*> Hi,
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*> For different parallel runs, NAMD will perform non-deterministically, in the
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*> sense that the order of completion of different processors (and even the work
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*> that is assigned to them) will likely change, altering the order of summed
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*> energies. Due to the non-associativity of floating point addition, you should
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*> eventually see slightly different energy values from two parallel runs of an
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*> identical trajectory.
*

I thought the non-reproducibility of simulations in NAMD was mainly

because of the Berendsen pressure controller employed, which gives random

kicks to particles every few steps. Whether or not the run is parallel, I

do not think the trajectories will be reproducible, although I have not

tested this myself.

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