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From "Phil Steitz (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-701) Seeding a default RNG
Date Fri, 04 Nov 2011 17:09:51 GMT

    [ https://issues.apache.org/jira/browse/MATH-701?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13144170#comment-13144170
] 

Phil Steitz commented on MATH-701:
----------------------------------

I thought about changing the default seeding in AbstractWell and agree that would be a good
idea.  I still like to supply the seed explicitly and document it in RandomDataImpl, though,
so users of that class know exactly what they are getting by default.  There is a little wrinkle
here, too that keeping the seeding expressed and documented in RandomDataImpl makes easier
to keep track of.  If we ever implement hashcode in RandomDataImpl (or the Well generators),
things could get messed up if it does not separate generator instances the way the system
identity haschcode does.
                
> Seeding a default RNG
> ---------------------
>
>                 Key: MATH-701
>                 URL: https://issues.apache.org/jira/browse/MATH-701
>             Project: Commons Math
>          Issue Type: Bug
>            Reporter: Gilles
>            Assignee: Gilles
>             Fix For: 3.0
>
>
> In "RandomDataImpl":
> {code}
> private RandomGenerator getRan() {
>     if (rand == null) {
>         rand = new JDKRandomGenerator();
>         rand.setSeed(System.currentTimeMillis());
>     }
>     return rand;
> }
> {code}
> The conditional branch is used by "sample()" in "AbstractContinuousDistribution".
> When several "...Distribution" objects are instantiated in a short time interval, they
are seeded with the same value.

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