[Numpy-discussion] matrix indexing question

Timothy Hochberg tim.hochberg@ieee....
Thu Mar 29 23:19:35 CDT 2007

On 3/29/07, Bill Baxter <wbaxter@gmail.com> wrote:
> On 3/30/07, Timothy Hochberg <tim.hochberg@ieee.org> wrote:
> > Note, however that you can't (for instance) multiply column vector with
> > a row vector:
> >
> > >>> (c)(r)
> > Traceback (most recent call last):
> >   ...
> > TypeError: Cannot matrix multiply columns with anything
> >
> That should be allowed.  (N,1)*(1,M) is just an (N,M) matrix with
> entries C[i,j] = A[i,0]*B[0,]

I thought about that a little, and while I agree that it could be allowed,
I'm not sure that it should be allowed. It's a trade off between a bit of
what I would guess is little used functionality with some enhanced error
checking (I would guess that usually row*column signals a mistake). However,
I don't care much one way or the other; it's not hard to allow.

I kind of like the idea of using call for multiply, though.  If it
> doesn't turn out to have any major down sides it could be a good way
> to give ndarray a concise syntax for "dot".

We'll see how it goes down this time. I've proposed using call before, since
I've thought the matrix situation was kind of silly for what seems like ages
now, but it always sinks without a ripple.



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