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https://issues.apache.org/jira/browse/MATH-701?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13143559#comment-13143559
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Gilles commented on MATH-701:
-----------------------------
IIRC we discarded the solution of passing a RNG in the distribution's
constructor because the "sample" methods was construed as syntactic sugar in
order to access the "RandomData" functionality from within the
"...Distribution" classes.
It was also argued that people who would use this API (instead of directly
instantiating a "RandomDataImpl" object) would be satisfied with a default RNG,
whatever was deemed the best choice by the CM developers. Thus, if another
generator is indeed better, we should just plug it in instead of the current
"JDKRandomGenerator".
In the same line of argument, the possibility of seeding was also supposed to
be given up in exchange for a "sample" API at the distribution level.
In "AbstractContinuousDistribution", we have:
{code}
protected final RandomDataImpl randomData = new RandomDataImpl();
{code}
In effect, there is no reason not to replace that statement with:
{code}
protected final RandomDataImpl randomData = new RandomDataImpl(new
Well44497a());
{code}
As as side note: I don't understand why there is a default constructor in
"RandomDataImpl"; since all the methods need a RNG, it does not make much sense
to allow the object to be constructed without one!
Second side note: Why not separate the "secure" alternatives into another
implementation? There would be "RandomData" (with a "nextHexString" method) and
a "SecureRandomData" (also with a "nextHexString" method, instead of the
current "nextSecureHexString").
Back to this report's issue: The parent class "AbstractWell" seems to suffer
from the same problem because the default constructor calls
{{System.currentTimeMillis()}}.
We should have a look at how "java.util.Random" seeds its default instances so
that they can claim (excerpt form Javadoc):
{noformat}
This constructor sets the seed of the random number generator to a value very
likely to be
distinct from any other invocation of this constructor.
{noformat}
> 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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