[Numpy-discussion] Two questions about PEP 465 dot product

Alexander Belopolsky ndarray at mac.com
Fri May 22 13:57:17 EDT 2015


On Thu, May 21, 2015 at 9:37 PM, Nathaniel Smith <njs at pobox.com> wrote:
>
> .. there's been some discussion of the possibility of
> adding specialized gufuncs for broadcasted vector-vector,
> vector-matrix, matrix-vector multiplication, which wouldn't do the
> magic vector promotion that dot and @ do.


This would be nice.  What I would like to see is some consistency between
multi-matrix
support in linalg methods and dot.

For example, when A is a matrix and b is a vector and

a = linalg.solve(A, b)

then

dot(A, a) returns b, but if either or both A and b are stacks, this
invariant does not hold.  I would like
to see a function (say xdot) that I can use instead of dot and have xdot(A,
a) return b whenever a = linalg.solve(A, b).

Similarly, if w,v =  linalg.eig(A), then dot(A,v) returns w * v, but only
if A is 2d.
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