The vecdot() function in the array API should be what you are looking for (note that the current implementation in numpy.array_api is incorrect, which I'm fixing at https://github.com/numpy/numpy/pull/21928). It works like dot() but it always applies the 1-D dot product case with broadcasting, and lets you specify the axis. We'd want this function to be added to the main numpy namespace as well.
Aaron Meurer On Tue, Jul 5, 2022 at 5:39 PM <rmccampbe...@gmail.com> wrote: > > Maybe I wasn't clear, I'm talking about the 1-dimensional vector product, but > applied to N-D arrays of vectors. Certainly dot products can be realized as > matrix products, and often are in mathematics for convenience, but matrices > and vectors are not the same thing, theoretically or coding wise. If I have > two (M, N, k) arrays a and b where k is the vector dimension, to dot product > them using matrix notation I have to do: > > (a[:, :, np.newaxis, :] @ b[:, :, :, np.newaxis])[:, :, 0, 0] > > Which I certainly don't find readable (I always have to scratch my head a > little bit to figure out whether the newaxis's are in the right places). If > this is a common operation in larger expressions, then it basically has to be > written as a separate function, which then someone reading the code may have > to look at for the semantics. It also breaks down if you want to write > generic vector functions that may be applied along different axes; then you > need to do something like > > np.squeeze(np.expand_dims(a, axis=axis) @ np.expand_dims(b, axis=axis+1), > (axis, axis+1)) > > (after normalizing the axis; if it's negative you'd need to do axis-1 and > axis instead). > > Compare this to the simplicity, composability and consistency of: > > a.dot(b, axis=-1) * np.cross(c, d, axis=-1).dot(e, axis=-1) / > np.linalg.norm(f, axis=-1) > > (the cross and norm operators already support an axis parameter) > _______________________________________________ > NumPy-Discussion mailing list -- numpy-discussion@python.org > To unsubscribe send an email to numpy-discussion-le...@python.org > https://mail.python.org/mailman3/lists/numpy-discussion.python.org/ > Member address: asmeu...@gmail.com _______________________________________________ NumPy-Discussion mailing list -- numpy-discussion@python.org To unsubscribe send an email to numpy-discussion-le...@python.org https://mail.python.org/mailman3/lists/numpy-discussion.python.org/ Member address: arch...@mail-archive.com
