[jira] [Commented] (SPARK-17027) PolynomialExpansion.choose is prone to integer overflow

["Sean Owen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-17027?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15418065#comment-15418065 ] 

Sean Owen commented on SPARK-17027:
-----------------------------------

Is the problem in the naive calculation of n choose k?

{code}
  private def choose(n: Int, k: Int): Int = {
    Range(n, n - k, -1).product / Range(k, 1, -1).product
  }
{code}

Let's just call http://commons.apache.org/proper/commons-math/apidocs/org/apache/commons/math3/util/CombinatoricsUtils.html#binomialCoefficient(int,%20int)

> PolynomialExpansion.choose is prone to integer overflow 
> --------------------------------------------------------
>
>                 Key: SPARK-17027
>                 URL: https://issues.apache.org/jira/browse/SPARK-17027
>             Project: Spark
>          Issue Type: Bug
>          Components: ML
>    Affects Versions: 1.6.0, 2.0.0
>            Reporter: Maciej Szymkiewicz
>            Priority: Minor
>
> Current implementation computes power of k directly and because of that it is susceptible to integer overflow on relatively small input (4 features, degree equal 10).  It would be better to use recursive formula instead.



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