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From "Gilles (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-899) A random crash of MersenneTwister random generator
Date Sun, 18 Nov 2012 17:44:58 GMT

    [ https://issues.apache.org/jira/browse/MATH-899?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13499852#comment-13499852
] 

Gilles commented on MATH-899:
-----------------------------

bq. it would be sufficient to do a proof by induction (sort of): [...]

Well, this could be said for any piece of code: we must have property <x>, so we write
code that implements <x>. ;)
We write unit tests that actually show that the code behaves as expected.

After spending quite some time on the attached code, I of course agree that it is complicated
in some situations. In this case, the code is simple enough as to not necessitates a unit
test.
But the issue will crop up again if we start introducing more "complicated" code (like the
utilities in the "java.util.concurrent" package).

So do I commit just the class and no unit test, or just the unit test of the synchronizing
wrapper?

                
> A random crash of MersenneTwister random generator
> --------------------------------------------------
>
>                 Key: MATH-899
>                 URL: https://issues.apache.org/jira/browse/MATH-899
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.0
>         Environment: Windows 7, JDK 1.7.05
>            Reporter: Alexander Nozik
>            Priority: Minor
>         Attachments: SynchronizedRandomGenerator.java, SynchronizedRandomGeneratorTest.java
>
>
> There is a very small probability that MersenneTwister generator gives a following error:

> java.lang.ArrayIndexOutOfBoundsException: 624
> in MersenneTwister.java line 253
> The error is completely random and its probability is about 1e-8.
> UPD: The problem most probably arises only in multy-thread mode.

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