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From danielblazevski <...@git.apache.org>
Subject [GitHub] flink pull request: [FLINK-1745] Add exact k-nearest-neighbours al...
Date Wed, 28 Oct 2015 18:29:23 GMT
Github user danielblazevski commented on the pull request:

    https://github.com/apache/flink/pull/1220#issuecomment-151942911
  
    @tillrohrmann I now have more time to go back and try to finalize this PR in the next
couple of weeks.  After debugging a bit, I noticed that in your modification of `partitionBox`,
the variable `center` is different before and after the call of `partitionBox` in `makeChildren`.
 For example, in `makeChildren` I added some lines to print to the console, namely
    ``` scala
         println("center before partitioning =  " + center)
          val cPart = partitionBox(center, width)
          println("cPart =  " + cPart)
          val mappedWidth = 0.5*width.asBreeze
          children = cPart.map(p => new Node(p, mappedWidth.fromBreeze, null))
          println("center after partitioning =  " + center)
    ```
    The output to console is
    ```
    center before partitioning =  DenseVector(0.0, 0.0)
    cPart =  List(DenseVector(-0.5, -0.25), DenseVector(-0.5, 0.25), DenseVector(0.5, -0.25),
DenseVector(0.5, 0.25))
    center after partitioning =  DenseVector(0.5, 0.25)
    ```
    So the output `cPart` looks good, but the value of `center` after partitioning should
still be `(0.0,0.0)`.  I'm confused as to how it is even changed to `(0.5, 0.25)` the final
entry of `cPart`, and hence not clear how to fix that.  I imagine it should be an easy fix;
of course I can use a hack to update `center` to be the average of `cPart`, but that seems
wasteful since `center`for a given node should not be changed.


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