[Numpy-discussion] Linear algebra functions on empty arrays

josef.pktd at gmail.com josef.pktd at gmail.com
Mon Sep 15 07:07:11 EDT 2014

On Mon, Sep 15, 2014 at 5:48 AM, Sebastian Berg
<sebastian at sipsolutions.net> wrote:
> Hey all,
> for https://github.com/numpy/numpy/pull/3861/files I would like to allow
> 0-sized dimensions for generalized ufuncs, meaning that the gufunc has
> to be able to handle this, but also that it *can* handle it at all.
> However lapack does not support this, so it needs some explicit fixing.
> Also some of the linalg functions currently explicitly allow and others
> explicitly disallow empty arrays.
> For example the QR and eigvals does not allow it, but on the other hand
> solve explicitly does (most probably never did, simply because lapack
> does not). So I am wondering if there is some convention for this, or
> what convention we should implement.

What does an empty square matrix/array look like?

np.linalg.solve   can have empty rhs, but shape of empty lhs, `a`, is ?

If I do a QR(arr)  with arr.shape=(0, 5), what is R supposed to be ?

I just wrote some loops over linalg.qr, but I always initialized explicitly.

I didn't manage to figure out how empty arrays would be useful.

If an empty square matrix can only only be of shape (0, 0), then it's
no use (in my applications).


> Regards,
> Sebastian
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