[Numpy-discussion] MapIter api

[Frédéric Bastien]

Hi,

this is currently used in Theano! In fact, it is a John S. that implemented
it in NumPy to allow fast gradient of the advanced indexing in Theano. It
allow code like:

matrix1[vector1, vector2] += matrix2

where there is duplicate indices in the vector

In looking at the code, I saw it use at least those part of the interface.

PyArrayMapIterObject
PyArray_MapIterNext
PyArray_ITER_NEXT
PyArray_MapIterSwapAxes
PyArray_BroadcastToShape

I lost the end of this discussion, but I think this is not possible in
NumPy as there was not an agreement to include that. But I remember a few
other user on this list asking for this(and they where Theano user to my
knowledge).

So I would prefer that you don't remove the part that we use for the next
1.8 release.

thanks

Frédéric


On Tue, Apr 16, 2013 at 9:54 AM, Nathaniel Smith <njs at pobox.com> wrote:

> On Mon, Apr 15, 2013 at 5:29 PM, Sebastian Berg
> <sebastian at sipsolutions.net> wrote:
> > Hey,
> >
> > the MapIter API has only been made public in master right? So it is no
> > problem at all to change at least the mapiter struct, right?
> >
> > I got annoyed at all those special cases that make things difficult to
> > get an idea where to put i.e. to fix the boolean array-like stuff. So
> > actually started rewriting it (and I already got one big function that
> > does all index preparation -- ok it is untested but its basically
> > there).
> >
> > I would guess it is not really a big problem even if it was public for
> > longer, since you shouldn't do those direct struct access probably? But
> > just checking.
>
> Why don't we just make the struct opaque, i.e., just declare it in the
> public header file and move the actual definition to an internal
> header file?
>
> If it's too annoying I guess we could even make it non-public, at
> least in 1.8 -- IIRC it's only there so we can use it in umath, and
> IIRC the patch to use it hasn't landed yet. Or we could just merge
> umath and multiarray into a single .so, that would save a *lot* of
> annoying fiddling with the public API that doesn't actually serve any
> purpose.
>
> -n
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