[Numpy-discussion] NEP for faster ufuncs

John Salvatier jsalvati@u.washington....
Tue Dec 21 20:00:49 CST 2010


I applaud you on your vision. I only have one small suggestion: I suggest
you put a table of contents at the beginning of your NEP so people may skip
to the part that most interests them.

On Tue, Dec 21, 2010 at 4:59 PM, John Salvatier
<jsalvati@u.washington.edu>wrote:

> That is an amazing christmas present.
>
> On Tue, Dec 21, 2010 at 4:53 PM, Mark Wiebe <mwwiebe@gmail.com> wrote:
>
>> Hello NumPy-ers,
>>
>> After some performance analysis, I've designed and implemented a new
>> iterator designed to speed up ufuncs and allow for easier multi-dimensional
>> iteration.  The new code is fairly large, but works quite well already.  If
>> some people could read the NEP and give some feedback, that would be great!
>>  Here's a link:
>>
>>
>> https://github.com/m-paradox/numpy/blob/mw_neps/doc/neps/new-iterator-ufunc.rst
>>
>> I would also love it if someone could try building the code and play
>> around with it a bit.  The github branch is here:
>>
>> https://github.com/m-paradox/numpy/tree/new_iterator
>>
>> To give a taste of the iterator's functionality, below is an example from
>> the NEP for how to implement a "Lambda UFunc."  With just a few lines of
>> code, it's possible to replicate something similar to the numexpr library
>> (numexpr still gets a bigger speedup, though).  In the example expression I
>> chose, execution time went from 138ms to 61ms.
>>
>> Hopefully this is a good Christmas present for NumPy. :)
>>
>> Cheers,
>> Mark
>>
>> Here is the definition of the ``luf`` function.::
>>
>>     def luf(lamdaexpr, *args, **kwargs):
>>         """Lambda UFunc
>>
>>             e.g.
>>             c = luf(lambda i,j:i+j, a, b, order='K',
>>                                 casting='safe', buffersize=8192)
>>
>>             c = np.empty(...)
>>             luf(lambda i,j:i+j, a, b, out=c, order='K',
>>                                 casting='safe', buffersize=8192)
>>         """
>>
>>         nargs = len(args)
>>         op = args + (kwargs.get('out',None),)
>>         it = np.newiter(op, ['buffered','no_inner_iteration'],
>>                 [['readonly','nbo_aligned']]*nargs +
>>                                 [['writeonly','allocate','no_broadcast']],
>>                 order=kwargs.get('order','K'),
>>                 casting=kwargs.get('casting','safe'),
>>                 buffersize=kwargs.get('buffersize',0))
>>         while not it.finished:
>>             it[-1] = lamdaexpr(*it[:-1])
>>             it.iternext()
>>
>>         return it.operands[-1]
>>
>> Then, by using ``luf`` instead of straight Python expressions, we
>> can gain some performance from better cache behavior.::
>>
>>     In [2]: a = np.random.random((50,50,50,10))
>>     In [3]: b = np.random.random((50,50,1,10))
>>     In [4]: c = np.random.random((50,50,50,1))
>>
>>     In [5]: timeit 3*a+b-(a/c)
>>     1 loops, best of 3: 138 ms per loop
>>
>>     In [6]: timeit luf(lambda a,b,c:3*a+b-(a/c), a, b, c)
>>     10 loops, best of 3: 60.9 ms per loop
>>
>>     In [7]: np.all(3*a+b-(a/c) == luf(lambda a,b,c:3*a+b-(a/c), a, b, c))
>>     Out[7]: True
>>
>>
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>>
>>
>
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