On Fri, Mar 14, 2014 at 9:32 PM, Nathaniel Smith <n...@pobox.com> wrote:
> > Here are the interesting use cases for @@ that I can think of: > - 'vector @@ 2' gives the squared Euclidean length (because it's the > same as vector @ vector). Kind of handy. > - 'matrix @@ n' of course gives the matrix power, which is of marginal > use but does come in handy sometimes, e.g., when looking at graph > connectivity. > - 'matrix @@ -1' provides a very transparent notation for translating > textbook formulas (with all their inverses) into code. It's a bit > unhelpful in practice, because (a) usually you should use solve(), and > (b) 'matrix @@ -1' is actually more characters than 'inv(matrix)'. But > sometimes transparent notation may be important. (And in some cases, > like using numba or theano or whatever, 'matrix @@ -1 @ foo' could be > compiled into a call to solve() anyway.) > > (Did I miss any?) > I'm not really arguing for it, and I am not sure how, or even if, it fits in the general scheme. But for completeness sake, 'e @@ Matrix' is used in some treatments of linear systems of differential equations, where: d<vector>/dt = <matrix> @ <vector> would have solution <vector> = e @@ (<matrix> * t) @ <vector_0> I don't think it makes any sense to use it as such in the context of numpy, as I think it would make broadcasting undecidable. But there may be parallel universes where having n @@ <matrix> and <matrix> @@ n both with well defined, yet different meanings may make sense. It is my impression that in this entirely made up scenario you would want e @@ A @@ 3 to be evaluated as (e @@ A) @@ 3. Which probably has more to do with the fact that the two @@ mean different things, than with the associativity that repeated calls to the same @@ should have. Personally I couldn't care less, and if I had a vote I would let @@ rest for now, until we see how @ plays out. Jaime
_______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
