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From Leanne Guy <>
Subject Re: (math] Percentile performance improvement
Date Wed, 03 Nov 2010 10:41:31 GMT
Hi Luc,

Sorry to not reply sooner, I have been away most of October.  I've tested
the snapshot with these changes and see the same level of performance 

So yes, this suits my needs. Thanks to everyone for their efforts

On 10/10/10 17:14 PM, Luc Maisonobe wrote:
> Hi all,
> The new implementation of Percentile improving performances has been
> checked in. It should solve issue
> <>.
> As discussed here, the implementation is based on a selection algorithm
> instead of a complete sort. A setData method has also been added to the
> AbstractUnivariateStatistic base class to allow caching some work
> between calls when several percentiles are requested. Both the
> partitioned data array and the first levels of pivots are cached. For
> now, I have set the limit to 10 levels of pivots, but this can be
> changed (the memory cost is a (2^n)-1 integer array for n levels).
>  From the few performances tests I have done, the improvements are really
> huge and depend on both the array size and the number of percentiles
> desired. Compared with a single cached sort followed by direct array
> accesses, the selection-based implementation is still about twice faster
> up to a few hundreds percentiles for array sizes of a few millions
> elements. For a single percentile, I saw up to a few hundreds times
> faster computation.
> Leanne, could you check this suits your needs ?
> Luc
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Leanne Guy
Variability Processing Group, Gaia Project, ESA
Observatoire de Geneve / ISDC Astrophysics Data Centre
Chemin d'Ecogia 16, CH-1290 Versoix,  Switzerland

Tel: +41 22 379 2151    Fax: +41 (0)22 37 92 135
WWW:   Skype: leanneobsge

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