On Wed, Aug 6, 2014 at 5:51 PM, Nathaniel Smith <n...@pobox.com> wrote:
> On 7 Aug 2014 00:41, "Charles R Harris" <charlesr.har...@gmail.com> wrote: > > > > On Wed, Aug 6, 2014 at 5:33 PM, Nathaniel Smith <n...@pobox.com> wrote: > >> > >> On Thu, Aug 7, 2014 at 12:24 AM, Charles R Harris > >> <charlesr.har...@gmail.com> wrote: > >> > > >> > On Wed, Aug 6, 2014 at 4:57 PM, Nathaniel Smith <n...@pobox.com> > wrote: > >> >> > >> >> On Wed, Aug 6, 2014 at 4:32 PM, Charles R Harris > >> >> <charlesr.har...@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? > >> > > > > Sure, but matvec and vecvec would not be supported by '@' except when > vec was 1d because there is no way to distinguish a stack of vectors from a > matrix or a stack of matrices. > > Yes. But @ can never be magic - either people will have to write something > extra to flip these flags on their array objects, or they'll have to write > something extra to describe which operation they want. @ was never intended > to cover every case, just the simple-but-super-common ones that dot covers, > plus a few more (simple broadcasting). We have np.add even though + exists > too... > I don't expect stacked matrices/vectors to be used often, although there are some areas that might make heavy use of them, so I think we could live with the simple implementation, it's just a bit of a wart when there is broadcasting of arrays. Just to be clear, the '@' broadcasting differs from the dot broadcasting, agreed? Chuck
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