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Subject: Re: [OMPI users] open-mpi behaviour on Fedora, Ubuntu, Debian and CentOS
From: jody (jody.xha_at_[hidden])
Date: 2010-04-25 10:41:55


I once got different results when running on a 64-Bit platform instead of
a 32 bit platform - if i remember correctly, the reason was that on the
32-bit platform 80bit extended precision floats were used but on the 64bit
platform only 64bit floats.

On Sun, Apr 25, 2010 at 3:39 AM, Fabian Hänsel <fabtagon_at_[hidden]> wrote:
> 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 openmpi.
>
> Best regards
>  Fabian
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