Just to clarify the problem a bit, it looks like you want to compute the squared euclidean distance between every vector in a and every vector in b, i.e., a distance matrix. Is that correct? Also, how big are d1,d2,d3?

If you *are* looking to compute the distance matrix I suspect your end goal is something beyond that. Could you describe what you are trying to do? I could be that scipy.spatial or scipy.cluster are what you should look at.

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Chuck