[SciPy-User] Sparse dot differs from numpy dot by 10^5

[Wagner Sebastian]

So, I can't get rid of this issue, because this error does not lie within scipy or numpy but in the design of floating point arithmetic?
At the end of the calculation (after 3 more operations) only two promille out of 1470 values do not differ, all others do differ from the third digit on (median of the difference).

Is there any chance to know which one of the two results is "more correct"?

Regards,
Sebastian

-----Ursprüngliche Nachricht-----
Von: scipy-user-bounces at scipy.org [mailto:scipy-user-bounces at scipy.org] Im Auftrag von Emanuele Olivetti
Gesendet: Freitag, 27. September 2013 09:37
An: scipy-user at scipy.org
Betreff: Re: [SciPy-User] Sparse dot differs from numpy dot by 10^5

On 09/27/2013 09:31 AM, Jerome Kieffer wrote:
> On Fri, 27 Sep 2013 07:12:06 +0000
> Wagner Sebastian <Sebastian.Wagner.fl at ait.ac.at> wrote:
>
>> When changing some algorithms from dense matrices to sparse matrices I stumbled over a discrepancy between the sparse-version of dot and numpy's dot. All open issues mentioning 'dot' do not apply.
> Floating point addition is not commutable ... the order you are 
> summing is important (in silico) while it is not on the paper.
>

If that is the problem, this is a detailed description:
  http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

Best,

Emanuele

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