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https://issues.apache.org/jira/browse/MAHOUT-1746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14599735#comment-14599735
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Ted Dunning commented on MAHOUT-1746:
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I think that this is more complicated than it looks.
I just wrote a test and got really strange results. The rate at which x*x !=
Math.pow(x,2) is not constant in my test and seems like there may be strange
interactions with the JIT.
> 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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