[SciPy-User] understanding machine precision

Bruce Southey bsouthey@gmail....
Tue Dec 14 13:59:43 CST 2010


On 12/14/2010 01:29 PM, Francesc Alted wrote:
> A Tuesday 14 December 2010 20:17:10 Nils Wagner escrigué:
>> Hi all,
>>
>> I am using ATLAS
>>
>> python -i try_deterministic.py
>>
>> lstsq
>> 0.0
>> 0.0
>> 0.0
>> 0.0
>> 0.0
> That's interesting.  Maybe Josef is using a threaded ATLAS?  I
> positively know that threading introduces variability in the order that
> the computations are done.  However, I'm not sure on why ATLAS has
> decided to use several threads for so small matrices ((100, 10)) :-/
>
Does this 'issue' occur with numpy's lstsq?

This is most probably due to the OS (Windows) and compiler as Skipper's 
post indicates and probably related to the cpu as well. It may be how 
the binaries are created relative to the target system especially if 
different compilers are used.

Overclocking and heat can also create issues (just as those people 
finding prime numbers :-) ).

Bruce






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