[Numpy-discussion] Detect subclass of ndarray

Charles R Harris charlesr.harris@gmail....
Sat Mar 24 10:33:30 CDT 2007

On 3/24/07, Alan G Isaac <aisaac@american.edu> wrote:
> On Fri, 23 Mar 2007, Charles R Harris apparently wrote:
> > the following gives the wrong result:
> > In [15]: I = matrix(eye(2))
> > In [16]: I*ones(2)
> > Out[16]: matrix([[ 1.,  1.]])
> > where the output should be a column vector.
> Why should this output a column?
> I would prefer an exception.
> Add the axis if you want it:
> I*ones(2)[:,None]
> works fine.

Because it is mathematically correct. You can't multiply a vector by a 2x2
matrix and get a 1x2 matrix as the result. Sure, there are work arounds, but
if matrix multiplication is going to work when mixed with arrays, it should
work correctly.

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