[jira] Commented: (MAHOUT-187) RandomUtils>>isNotPrime throws IllegalArgumentException when argument is less than 2.

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

    [ https://issues.apache.org/jira/browse/MAHOUT-187?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12766565#action_12766565 ] 

Sean Owen commented on MAHOUT-187:
----------------------------------

I agree, and now I am scratching my head to remember why on earth I would have written this. Let me think about it a sec but in all likelihood I will just make this change.

> RandomUtils>>isNotPrime throws IllegalArgumentException when argument is less than 2.
> -------------------------------------------------------------------------------------
>
>                 Key: MAHOUT-187
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-187
>             Project: Mahout
>          Issue Type: Bug
>    Affects Versions: 0.1
>            Reporter: Emerson Murphy-HIll
>             Fix For: 0.2
>
>
> I was using a FastMap, which happened to be empty, and rehash() was called.  Rehash eventually calls isNotPrime where n=1, which throws an illegal argument exception:
>   public static boolean isNotPrime(int n) {
>     if (n < 2) {
>       throw new IllegalArgumentException();
>     }
> It seems to me anything less than two is not prime.  Thus, I suggest:
>   public static boolean isNotPrime(int n) {
>     if (n < 2) {
>     	return true;
>     }

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