[Numpy-discussion] defmatrix.py
Colin J. Williams
cjw@sympatico...
Tue Mar 27 13:08:12 CDT 2007
Charles R Harris wrote:
>
>
> On 3/26/07, *Travis Oliphant* <oliphant@ee.byu.edu
> <mailto:oliphant@ee.byu.edu>> wrote:
>
>
> > I think that might be the simplest thing, dot overrides subtypes.
> BTW,
> > here is another ambiguity
> >
> > In [6]: dot(array([[1]]),ones(2))
> >
> ---------------------------------------------------------------------------
>
> > exceptions.ValueError Traceback (most
> > recent call last)
> >
> > /home/charris/<ipython console>
> >
> > ValueError: matrices are not aligned
> >
> > Note that in this case dot acts like the rhs is always a column
> vector
> > although it returns a 1-d vector. I don't know that this is a bad
> > thing, but perhaps we should extend this behaviour to matrices,
> which
> > would be different from the now current 1-d is always a *row*
> vector, i.e.
>
>
> The rule 1-d is always a *row* vector only applies when converting to a
> matrix.
>
> In this case, the dot operator does not "convert to a matrix" but uses
> rules for operating with mixed 2-d and 1-d arrays inherited from
> Numeric.
>
> I'm very hesitant to change those rules.
>
>
> I wasn't suggesting that, just noticing that the rule was 1-d vector on
> right is treated as a column vector by dot, which is why an exception
> was raised in the posted case. If it is traditional for matrix routines
> always treat is as a row vector, so be it.
My recollection is that text books treat the column vector, represented
by a lower case letter, bold or underlined, as the default. If b
(dressed as described before) is a column vector, then b' represents a
row vector.
For numpy, it makes sense to consider b as a row vector, since the
underlying array uses the C convention where each row is stored
contiguously.
Colin W.
>
> Chuck
>
>
>
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>
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