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Re: Nearest neighbours of points

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Am 25.10.15 um 00:44 schrieb Poul Riis:
> A program that does what I want can be found below. However, I want
> to know if there is a faster way because I have many moving points
> and the two nearest neighbours must be identified a lot of times.
>

Ah, that changes the game. But I'm still puzzled - is this first scipy 
function fast enough? Because your second computation using teh nested 
for loops in my tests gave exactly the same index. I'm not sure it is 
guaranteed, but it seems that the pdist function uses the same ordering 
as your code. In which case you can simply calculate i and j from the 
index n.

For instance, if you have i and j, you can compute n by the formula:

print('The index computed: ', N*istore-istore-istore*(istore+1)/2+jstore-1)

Now you are left with determining i and j from n. You need to find the 
largest i such that the j from solving the above equation is not 
negative. If you are lazy, and it is fast enough, you can compute this 
value in a loop - it is O(n). Or you can try solvin it as a quadratic 
inequation for i.


	Christian

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Thread

Nearest neighbours of points Poul Riis <priisdk@gmail.com> - 2015-10-24 13:05 -0700
  Re: Nearest neighbours of points Christian Gollwitzer <auriocus@gmx.de> - 2015-10-24 22:45 +0200
  Re: Nearest neighbours of points Poul Riis <priisdk@gmail.com> - 2015-10-24 15:44 -0700
    Re: Nearest neighbours of points Christian Gollwitzer <auriocus@gmx.de> - 2015-10-25 09:55 +0100
      Re: Nearest neighbours of points Poul Riis <priisdk@gmail.com> - 2015-10-25 05:00 -0700
      Re: Nearest neighbours of points Peter Pearson <pkpearson@nowhere.invalid> - 2015-10-25 17:01 +0000
    Re: Nearest neighbours of points Bartc <bc@freeuk.com> - 2015-10-25 12:36 +0000
  Re: Nearest neighbours of points Fabien <fabien.maussion@gmail.com> - 2015-10-26 03:25 +0100
  Re: Nearest neighbours of points Tom P <werotizy@freent.dd> - 2015-10-31 22:28 +0100
    Re: Nearest neighbours of points Terry Reedy <tjreedy@udel.edu> - 2015-10-31 23:00 -0400

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