[Numpy-discussion] vectorizing loops

David M. Cooke cookedm at physics.mcmaster.ca
Thu Nov 1 10:14:45 EDT 2007

On Nov 1, 2007, at 08:56 , Francesc Altet wrote:

> A Wednesday 31 October 2007, Timothy Hochberg escrigué:
>> On Oct 31, 2007 3:18 AM, Francesc Altet <faltet at carabos.com> wrote:
>> [SNIP]
>>> Incidentally, all the improvements of the PyTables flavor of
>>> numexpr have been reported to the original authors, but, for the
>>> sake of keeping numexpr simple, they decided to implement only some
>>> of them. However, people is encouraged to try out the Pytables
>>> flavor from:
>> My original concern was that we'd start overflowing the code cache
>> and slow things down. Some experiments seemed to confirm this on some
>> processors, but it then turned out those were in error. At least
>> that's my recollection. Because of that, and because PyTables is, as
>> far as I know, the major user of numexpr, I suspect I'd be fine
>> putting those changes in now. I say "suspect" since it's been a long
>> time since I looked at the relevant patches, and I should probably
>> look at those again before I commit myself. I just haven't had the
>> free time and motivation to go back and look at the patches.  I can't
>> speak for David though.
> If I remember correctly, another point where you (specially David)  
> were
> not very keen to include was the support for strings, arguing that
> numexpr is meant mainly to deal with numerical data, not textual.
> However, our experience is that adding this support was not too
> complicated (mainly due to NumPy flexibility), and can be helpful in
> some instances.  As for one, we use them for evaluating expressions
> like 'array_string == "some_string"', and this can be very convenient
> to use when you are in the middle of potentially complex boolean
> expressions that you want to evaluate *fast*.
> At any rate, we would be glad if you would like to integrate our  
> patches
> in the main numexpr, as there is not much sense to have different
> implementations of numexpr (most specially when it seems that there  
> are
> not much users out there).  So, count on us for any question you may
> have in this regard.

Well, I don't have much time to work on it, but if you make sure your  
patches on the scipy Trac apply clean, I'll have a quick look at them  
and apply them. Since you've had them working in production code, they  
should be good ;-)

Another issue is that numexpr is still in the scipy sandbox, so only  
those who enable it will use it (or use it through PyTables). One  
problem with moving it out is that Tim reports the compile times on  
Windows are ridiculous (20 mins!). Maybe numexpr should become a  
scikit? It certainly doesn't need the rest of scipy.

|David M. Cooke              http://arbutus.physics.mcmaster.ca/dmc/
|cookedm at physics.mcmaster.ca

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