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From tillrohrmann <...@git.apache.org>
Subject [GitHub] flink pull request: FLINK-1737: Kronecker product
Date Mon, 23 Nov 2015 15:27:31 GMT
Github user tillrohrmann commented on a diff in the pull request:

    https://github.com/apache/flink/pull/1078#discussion_r45615836
  
    --- Diff: flink-staging/flink-ml/src/main/scala/org/apache/flink/ml/math/DenseVector.scala
---
    @@ -102,6 +102,38 @@ case class DenseVector(
         }
       }
     
    +  /** Returns the outer product (a.k.a. Kronecker product) of `this`
    +    * with `other`. The result will given in [[org.apache.flink.ml.math.SparseMatrix]]
    +    * representation if `other` is sparse and as [[org.apache.flink.ml.math.DenseMatrix]]
otherwise.
    +    *
    +    * @param other a Vector
    +    * @return the [[org.apache.flink.ml.math.Matrix]] which equals the outer product
of `this`
    +    *         with `other.`
    +    */
    +  override def outer(other: Vector): Matrix = {
    +    val numRows = size
    +    val numCols = other.size
    +
    +    other match {
    +      case sv @ SparseVector(_, _, _) =>
    +        val entries = for {
    +          i <- 0 until numRows
    +          j <- sv.indices
    +          value = this(i) * sv.data(sv.indices.indexOf(j))
    --- End diff --
    
    `sv.indices.indexOf(j)` will in the best case always trigger a binary search. Why not
doing `(j, idxJ) <- sv.indices.zipWithIndex` and then using `idxJ` here?


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