At some point, someone is going to make a single documentation page describing all of this, right? Tables, mathtex, and such? I get woozy whenever I see this discussion go on.
Ben Root On Fri, May 22, 2015 at 2:23 PM, Nathaniel Smith <n...@pobox.com> wrote: > On May 22, 2015 11:00 AM, "Alexander Belopolsky" <ndar...@mac.com> wrote: > > > > > > On Thu, May 21, 2015 at 9:37 PM, Nathaniel Smith <n...@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). > > I believe this equivalence holds if xdot(x, y) = x @ y, because solve() > does follow the pep 465 semantics for shape handling. Or at least, it's > intended to. Of course we will also expose pep 465 matmul semantics under > some name that doesn't require the new syntax (probably not "xdot" though > ;-)). > > > Similarly, if w,v = linalg.eig(A), then dot(A,v) returns w * v, but > only if A is 2d. > > Again A @ v I believe does the right thing, though I'm not positive -- you > might need a swapaxes or matvec or something. Let us know if you work it > out :-). > > Note that it still won't be equivalent to w * v because w * v doesn't > broadcast the way you want :-). You need w[..., np.newaxis, :] * v, I think. > > -n > > > > > > > _______________________________________________ > > NumPy-Discussion mailing list > > NumPy-Discussion@scipy.org > > http://mail.scipy.org/mailman/listinfo/numpy-discussion > > > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion > >
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