[ 
https://issues.apache.org/jira/browse/FLINK-1737?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14909813#comment-14909813
 ] 

ASF GitHub Bot commented on FLINK-1737:
---------------------------------------

Github user daniel-pape commented on a diff in the pull request:

    https://github.com/apache/flink/pull/1078#discussion_r40507074
  
    --- Diff: 
flink-staging/flink-ml/src/main/scala/org/apache/flink/ml/math/SparseVector.scala
 ---
    @@ -85,6 +85,34 @@ case class SparseVector(
         }
       }
     
    +  /** Returns the outer product (a.k.a. Kronecker product) of `this`
    +    * with `other`. The result is given in 
[[org.apache.flink.ml.math.SparseMatrix]]
    +    * representation.
    +    *
    +    * @param other a Vector
    +    * @return the [[org.apache.flink.ml.math.SparseMatrix]] which equals 
the outer product of `this`
    +    *         with `other.`
    +    */
    +  override def outer(other: Vector): SparseMatrix = {
    +    val numRows = size
    +    val numCols = other.size
    +
    +    val otherIndices = other match {
    +      case sv @ SparseVector(_, _, _) => sv.indices
    +      case dv @ DenseVector(_) => (0 until dv.size).toArray
    +    }
    +
    +    val entries = for {
    +      i <- indices
    +      j <- otherIndices
    +      value = this(i) * other(j)
    --- End diff --
    
    Thanks for pointing this out. 


> Add statistical whitening transformation to machine learning library
> --------------------------------------------------------------------
>
>                 Key: FLINK-1737
>                 URL: https://issues.apache.org/jira/browse/FLINK-1737
>             Project: Flink
>          Issue Type: New Feature
>          Components: Machine Learning Library
>            Reporter: Till Rohrmann
>            Assignee: Daniel Pape
>              Labels: ML, Starter
>
> The statistical whitening transformation [1] is a preprocessing step for 
> different ML algorithms. It decorrelates the individual dimensions and sets 
> its variance to 1.
> Statistical whitening should be implemented as a {{Transfomer}}.
> Resources:
> [1] [http://en.wikipedia.org/wiki/Whitening_transformation]



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