[Numpy-discussion] accumulation operation

Executing the following code,

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import numpy as np a = np.zeros((3,)) w = np.array([0, 1, 0, 1, 2]) v = np.array([10.0, 1, 10.0, 2, 9]) a[w] += v

I was expecting 'a' to be array([20., 3., 9.]. Instead I get

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a array([ 10., 2., 9.])

This with numpy version 1.6.1. Is there another way to do the accumulation I want? Thanks, Ralf