[Numpy-discussion] Why do mgrid and meshgrid not return broadcast arrays?
jni.soma at gmail.com
Wed Mar 8 21:48:45 EST 2017
I was a bit surprised to discover that both meshgrid nor mgrid return fully instantiated arrays, when simple broadcasting (ie with stride=0 for other axes) is functionally identical and happens much, much faster.
I wrote my own function to do this:
shape = tuple(map(len, arrays))
ndim = len(shape)
result = 
for i, arr in enumerate(arrays, start=1):
reshaped = np.broadcast_to(arr[[...] + [np.newaxis] * (ndim - i)],
For even a modest-sized 512 x 512 grid, this version is close to 100x faster:
In : %timeit th.broadcast_mgrid((np.arange(512), np.arange(512)))
10000 loops, best of 3: 25.9 µs per loop
In : %timeit np.meshgrid(np.arange(512), np.arange(512))
100 loops, best of 3: 2.02 ms per loop
In : %timeit np.mgrid[:512, :512]
100 loops, best of 3: 4.84 ms per loop
Is there a conscious design decision as to why this isn’t what meshgrid/mgrid do already? Or would a PR be welcome to do this?
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