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From "Andrew Musselman (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAHOUT-1746) Fix: mxA ^ 2, mxA ^ 0.5 to mean the same thing as mxA * mxA and mxA ::= sqrt _
Date Tue, 23 Jun 2015 23:59:43 GMT

    [ https://issues.apache.org/jira/browse/MAHOUT-1746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14598609#comment-14598609
] 

Andrew Musselman commented on MAHOUT-1746:
------------------------------------------

I can do it on the weekend unless you want to.

> Fix: mxA ^ 2, mxA ^ 0.5 to mean the same thing as mxA * mxA and mxA ::= sqrt _
> ------------------------------------------------------------------------------
>
>                 Key: MAHOUT-1746
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-1746
>             Project: Mahout
>          Issue Type: Blog - New Blog Request
>            Reporter: Dmitriy Lyubimov
>            Assignee: Dmitriy Lyubimov
>             Fix For: 0.10.2
>
>
> it so happens that in java, if x is of double type, Math.pow(x,2.0) and x * x produce
different values approximately once in million random values.
> This is extremely annoying as it creates rounding errors, especially with things like
euclidean distance computations, which eventually may produce occasional NaNs. 
> This issue suggests to get special treatment on vector and matrix dsl to make sure identical
fpu algorithms are running as follows:
> x ^ 2 <=> x * x
> x ^ 0.5 <=> sqrt(x)



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