[Numpy-discussion] Is this a bug?

[Charles R Harris]

On Tue, Sep 16, 2014 at 1:55 PM, <josef.pktd at gmail.com> wrote:

> On Tue, Sep 16, 2014 at 3:42 PM, Nathaniel Smith <njs at pobox.com> wrote:
> > On Tue, Sep 16, 2014 at 3:27 PM, Charles R Harris
> > <charlesr.harris at gmail.com> wrote:
> >> Hi All,
> >>
> >> It turns out that gufuncs will broadcast the last dimension if it is
> one.
> >> For instance, inner1d has signature `(n), (n) -> ()`, yet
> >>
> >> In [27]: inner1d([1,1,1], [1])
> >> Out[27]: 3
> >
> > Yes, this looks totally wrong to me too... broadcasting is a feature
> > of auto-vectorizing a core operation over a set of dimensions, it
> > shouldn't be applied to the dimensions of the core operation itself
> > like this.
>
> Are these functions doing any numerical shortcuts in this case?
>
> If yes, this would be convenient.
>
> inner1d(x, weights)   with weights is either (n, ) or ()
>
> if weights == 1:
>     return x.sum()
> else:
>     return inner1d(x, weights)
>
>
That depends on the inner inner loop ;) Currently inner1d inner loop
multiplies and adds so not as efficient as a sum in the scalar case.
However, it is probably faster than an if statement.

In [4]: timeit inner1d(a, 1)
10000 loops, best of 3: 56.4 µs per loop

In [5]: timeit a.sum()
10000 loops, best of 3: 48.3 µs per loop

Chuck
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