[Numpy-discussion] Changes to generalized ufunc core dimension checking

Feng Yu rainwoodman at gmail.com
Fri Mar 18 13:25:44 EDT 2016

Thanks for the explanation. I see the point now.

On Thu, Mar 17, 2016 at 3:21 PM, Nathaniel Smith <njs at pobox.com> wrote:
> On Thu, Mar 17, 2016 at 2:04 PM, Feng Yu <rainwoodman at gmail.com> wrote:
>> Hi,
>> ang2pix is used in astronomy to pixelize coordinate in forms of
>> (theta, phi). healpy is a binding of healpix
>> (http://healpix.sourceforge.net/, introduction there too), plus a lot
>> of more extra features or bloat (and I am not particular fond of this
>> aspect of healpy). It gets the work done.
>> You can think of the function ang2pix as nump.digitize for angular input.
>> 'nside' and 'nest' controls the number of pixels and the ordering of
>> pixels (since it is 2d to linear index).
>> The important thing here is ang2pix is a pure function from (nside,
>> nest, theta, phi) to pixelid, so in principle it can be written as a
>> ufunc to extend the functionality to generate pixel ids for different
>> nside and nest settings in the same function call.
> Thanks for the details!
> From what you're saying, it sounds like ang2pix actually wouldn't care
> either way about the gufunc broadcasting changes we're talking about.
> When we talk about *g*eneralized ufuncs, we're referring to ufuncs
> where the "core" minimal operation that gets looped over is already
> intrinsically something that operates on arrays, not just scalars --
> so operations like matrix multiply, sum, mean, mode, sort, etc., which
> you might want to apply simultaneously to a whole bunch of arrays, and
> the question is about how to handle these "inner" dimensions. In this
> case it sounds like (nside, nest, theta, phi) are 4 scalars, right? So
> this would just be a regular ufunc, and the whole issue doesn't arise.
> Broadcast all you like :-)
> -n
> --
> Nathaniel J. Smith -- https://vorpus.org
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