[Numpy-discussion] Proposal: Chaining np.dot with mdot helper function

Nathaniel Smith njs at pobox.com
Thu Feb 20 10:02:09 EST 2014

If you send a patch that deprecates dot's current behaviour for ndim>2,
we'll probably merge it. (We'd like it to function like you suggest, for
consistency with other gufuncs. But to get there we have to deprecate the
current behaviour first.)

While I'm wishing for things I'll also mention that it would be really neat
if binary gufuncs would have a .outer method like regular ufuncs do, so
anyone currently using ndim>2 dot could just switch to that. But that's a
lot more work than just deprecating something :-).

On 20 Feb 2014 09:27, "Eric Moore" <ewm at redtetrahedron.org> wrote:

> On Thursday, February 20, 2014, Eelco Hoogendoorn <
> hoogendoorn.eelco at gmail.com> wrote:
>> If the standard semantics are not affected, and the most common
>> two-argument scenario does not take more than a single if-statement
>> overhead, I don't see why it couldn't be a replacement for the existing
>> np.dot; but others mileage may vary.
>> On Thu, Feb 20, 2014 at 11:34 AM, Stefan Otte <stefan.otte at gmail.com>wrote:
>>> Hey,
>>> so I propose the following.  I'll implement a new function `mdot`.
>>> Incorporating the changes in `dot` are unlikely. Later, one can still
>>> include
>>> the features in `dot` if desired.
>>> `mdot` will have a default parameter `optimize`.  If `optimize==True` the
>>> reordering of the multiplication is done.  Otherwise it simply chains the
>>> multiplications.
>>> I'll test and benchmark my implementation and create a pull request.
>>> Cheers,
>>>  Stefan
>>> _______________________________________________
>>> NumPy-Discussion mailing list
>>> NumPy-Discussion at scipy.org
>>> http://mail.scipy.org/mailman/listinfo/numpy-discussion
>> Another consideration here is that we need a better way to work with
> stacked matrices such as np.linalg handles now.  Ie I want to compute the
> matrix product of two (k, n, n) arrays producing a (k,n,n) result.  Near
> as  I can tell there isn't a way to do this right now that doesn't involve
> an explicit loop. Since dot will return a (k, n, k, n) result. Yes this
> output contains what I want but it also computes a lot of things that I
> don't want too.
> It would also be nice to be able to do a matrix product reduction, (k, n,
> n) -> (n, n) in a single line too.
> Eric
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