[Numpy-discussion] Preliminary thoughts on implementing __matmul__

Nathaniel Smith njs at pobox.com
Wed Aug 6 19:33:13 EDT 2014

On Thu, Aug 7, 2014 at 12:24 AM, Charles R Harris
<charlesr.harris at gmail.com> wrote:
> On Wed, Aug 6, 2014 at 4:57 PM, Nathaniel Smith <njs at pobox.com> wrote:
>> On Wed, Aug 6, 2014 at 4:32 PM, Charles R Harris
>> <charlesr.harris at gmail.com> wrote:
>> > Should also mention that we don't have the ability to operate on stacked
>> > vectors because they can't be identified by dimension info. One
>> > workaround
>> > is to add dummy dimensions where needed, another is to add two flags,
>> > row
>> > and col, and set them appropriately. Two flags are needed for backward
>> > compatibility, i.e., both false is a traditional array.
>> It's possible I could be convinced to like this, but it would take a
>> substantial amount of convincing :-). It seems like a pretty big
>> violation of orthogonality/"one obvious way"/etc. to have two totally
>> different ways of representing row/column vectors.
> The '@' operator supports matrix stacks, so it would seem we also need to
> support vector stacks. The new addition would only be effective with the '@'
> operator. The main problem I see with flags is that adding them would
> require an extensive audit of the C code to make sure they were preserved.
> Another option, already supported to a large extent, is to have row and col
> classes inheriting from ndarray that add nothing, except for a possible new
> transpose type function/method. I did mock up such a class just for fun, and
> also added a 'dyad' function. If we really don't care to support stacked
> vectors we can get by without adding anything.

It's possible you could convince me that this is a good idea, but I'm
starting at like -0.95 :-). Wouldn't it be vastly simpler to just have
np.linalg.matvec, matmat, vecvec or something (each of which are
single-liners in terms of @), rather than deal with two different ways
of representing row/column vectors everywhere?


Nathaniel J. Smith
Postdoctoral researcher - Informatics - University of Edinburgh

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