[Numpy-discussion] "Extended" Outer Product

Anne Archibald peridot.faceted@gmail....
Thu Sep 20 01:16:11 CDT 2007

On 19/09/2007, Travis E. Oliphant <oliphant@enthought.com> wrote:
> Anne Archibald wrote:
> > vectorize, of course, is a good example of my point above: it really
> > just loops, in python IIRC, but conceptually it's extremely handy for
> > doing exactly what the OP wanted. Unfortunately vectorize() does not
> > yield a sufficiently ufunc-like object to support .outer(), as that
> > would be extremely tidy.
> >
> I'm not sure what you mean by sufficiently ufunc-like.  In fact,
> vectorize is a ufunc (it's just an object-based one).  Thus, it should
> produce what you want (as long as you use newaxis so that the
> broadcasting is done).   If you just want it to support the .outer
> method that could be easily done (as under the covers is a real ufunc).
> I just over-looked adding these methods to the result of vectorize.
> The purpose of vectorize is to create a ufunc out of a scalar-based
> function, so I don't see any problem in giving them the methods of
> ufuncs as well (as long as the signature is right --- 2 inputs and 1
> output).

Ah. You got it in one: I was missing the methods. It would be handy to
have them back, not least because then I could just remember the rule
"all binary ufuncs have .outer()".

Do ternary ufuncs support outer()? It would presumably just generate a
higher-rank array, for example
U.outer(arange(10),arange(11),arange(12)) would produce an array of
shape (10,11,12)... maybe there aren't any ternary ufuncs yet, apart
from the ones that are generated by vectorize(). I suppose ix_
provides an alternative, so that you could have

def outer(self,*args):
    return self(ix_(*args))

Still, I think for conceptual tidiness it would be nice if the ufuncs
vectorize() makes supported the methods.


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