[Numpy-discussion] finding close together points.
bergstrj at iro.umontreal.ca
Tue Nov 10 20:22:11 EST 2009
On Tue, Nov 10, 2009 at 8:17 PM, Christopher Barker
<Chris.Barker at noaa.gov> wrote:
> James Bergstra wrote:
>> In some cases a brute-force approach is also good.
>> If r is a matrix of shape Nx2:
>> (r*r).sum(axis=1) -2 * numpy.dot(r, r.T) +
>> (r*r).sum(axis=1).reshape((r.shape, 1)) < thresh**2
>> It's brute force, but it takes advantage of fast matrix multiplication.
> I'm more concerned about memory -- doesn't this use N^2 memory? Which
> could be an issue here.
Yes, this uses N^2 time and space. It's not a good algorithm when N is large.
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