[SciPy-User] understanding machine precision

josef.pktd@gmai... josef.pktd@gmai...
Wed Dec 15 06:36:44 CST 2010


On Tue, Dec 14, 2010 at 2:59 PM, Bruce Southey <bsouthey@gmail.com> wrote:
> 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?

good question, I didn't think about it.

same problem and my numpy is from an official installer (1.4.0) and
not compiled against the old ATLAS, that I'm still using.

>
> 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.

Skipper mentioned mkl, so I guess his scipy is compiled with microsoft
visual, while mine is compiled with MingW.

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

I don't think my Dell factory notebook is overclocked.

Josef

>
> Bruce
>
>
>
>
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