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Subject: Re: [OMPI users] open-mpi behaviour on Fedora, Ubuntu, Debian and CentOS
From: Asad Ali (asad06_at_[hidden])
Date: 2010-04-25 22:27:57

Hi Fabian,

Hi Asad,

>> I
>> found that running the same source code on these OS, with the same
>> versions of of gcc and open-mpi installed on them, gives different
>> results than Fedora and Ubuntu after a few hundred iterations. The first
>> few hundered iterations are exactly similar to that of Fedora and
>> Ubuntu but then it starts giving different results.

> Are you also using the same hardware? Different hardware platforms may
> exhibit different rounding behaviour. After some dependent interations
> such effects might indeed sum up and yield different results. The issue
> is called numeric (in)stability and is not specifically related to

Yes I use different machines such as

machine 1 uses AMD Opterons. (Fedora)

machine 2 and 3 use Intel Xeons. (CentOS)

machine 4 uses slightly older Intel Xeons. (Debian)

Only machine 1 gives correct results. While CentOS and Debian results are
same but are wrong and different from those of machine 1.


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