[Numpy-discussion] matrix default to column vector?

Olivier Verdier zelbier@gmail....
Sun Jun 7 02:43:33 CDT 2009


There would be a much simpler solution than allowing a new operator. Just
allow the numpy function dot to take more than two arguments. Then A*B*C in
matrix notation would simply be:
dot(A,B,C)

with arrays. Wouldn't that make everybody happy? Plus it does not break
backward compatibility. Am I missing something?

== Olivier

2009/6/7 Tom K. <tpk@kraussfamily.org>

>
>
> Fernando Perez wrote:
> >
> > On Sat, Jun 6, 2009 at 11:03 AM, Charles R
> > Harris<charlesr.harris@gmail.com> wrote:
> >
> >> I don't think we can change the current matrix class, to do so would
> >> break
> >> too much code. It would be nice to extend it with an explicit inner
> >> product,
> >> but I can't think of any simple notation for it that python would parse.
> >
> > Maybe it's time to make another push on python-dev for the pep-225
> > stuff for other operators?
> >
> > https://cirl.berkeley.edu/fperez/static/numpy-pep225/
> >
> > Last year I got pretty much zero interest from python-dev on this, but
> > they were very very busy with 3.0 on the horizon.  Perhaps once they
> > put 3.1 out would be a good time to champion this again.
> >
> > It's slightly independent of the matrix class debate, but perhaps
> > having special operators for real matrix multiplication could ease
> > some of the bottlenecks of this discussion.
> >
> > It would be great if someone could champion that discussion on
> > python-dev though, I don't see myself finding the time for it another
> > time around...
> >
>
> How about pep 211?
> http://www.python.org/dev/peps/pep-0211/
>
> PEP 211 proposes a single new operator (@) that could be used for matrix
> multiplication.
> MATLAB has elementwise versions of multiply, exponentiation, and left and
> right division using a preceding "." for the usual matrix versions (* ^ \
> /).
> PEP 225 proposes "tilde" versions of + - * / % **.
>
> While PEP 225 would allow a matrix exponentiation and right divide, I think
> these things are much less  common than matrix multiply.  Plus, I think
> following through with the PEP 225 implementation would create a
> frankenstein of a language that would be hard to read.
>
> So, I would argue for pushing for a single new operator that can then be
> used to implement "dot" with a binary infix operator.  We can resurrect PEP
> 211 or start a new PEP or whatever, the main thing is to have a proposal
> that makes sense.  Actually, what do you all think of this:
>  @ --> matrix multiply
>  @@ --> matrix exponentiation
> and we leave it at that - let's not get too greedy and try for matrix
> inverse via @/ or something.
>
> For the nd array operator, I would propose taking the last dimension of the
> left array and "collapsing" it with the first dimension of the right array,
> so
>  shape (a0, ..., aL-1,k) @ (k, b0, ..., bM-1) --> (a0, ..., aL-1, b0, ...,
> bM-1)
> Does that make sense?
>
> With this proposal, matrices go away and all our lives are sane again. :-)
> Long live the numpy ndarray!  Thanks to the creators for all your hard work
> BTW - I love this stuff!
>
>  - Tom K.
> --
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