c = a + b: 3N c = a + 2*b: 4N Does python garbage collect mid-expression? I.e. :
C = (a + 2*b) + b 4 or 5 N? Also note that when memory gets tight, fragmentation can be a problem. I.e. if two size-n arrays where just freed, you still may not be able to allocate a size-2n array. This seems to be worse on windows, not sure why. a += b: 2N np.add(a, b, out=a): 2N b *= 2; a += b: 2N Note that simply loading a and b requires 2N memory, so the latter code samples are near-optimal. And will run quite a bit faster for large arrays--pushing that memory around takes time. -Chris
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