RandomDataImpl uses both JDKRandomGenerator and Well19937c, while
contract/javadoc only specifies Well19937c.
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Key: MATH-720
URL: https://issues.apache.org/jira/browse/MATH-720
Project: Commons Math
Issue Type: Bug
Affects Versions: 3.0
Reporter: Dennis Hendriks
Attachments: TestRandom.java
See attached unit test. I create a distribution, sample it (not printed), set
the seed to 0, and then print the next sample. I also create the same
distribution again, set the seed to 0, and then print the next sample. I expect
the same sample, as in both cases the seed was set to 0, just before sampling.
I however get this output:
{code}
5
4
{code}
The problem is in the org.apache.commons.math.random.RandomDataImpl class:
- The RandomDataImpl(RandomGenerator rand) constructor states in javadoc:
"@param rand the source of (non-secure) random data (may be null, resulting in
default JDK-supplied generator)"
- reSeed(long seed) method does: if (rand == null) rand = new
JDKRandomGenerator();
- reSeed() method does: if (rand == null) rand = new JDKRandomGenerator();
- class javadoc states: "If no <code>RandomGenerator</code> is provided in the
constructor, the default is to use a Well19937c generator."
- getRan() does: if (rand == null) rand = new
Well19937c(System.currentTimeMillis() + System.identityHashCode(this));
- getRan() states in javadoc: "Creates and initializes a default generator if
null. Uses a Well19937c generator with System.currentTimeMillis() +
System.identityHashCode(this)) as the default seed."
It seems that only Well19937c should be used, but the constructor javadoc, and
the implementation of the reSeed methods was not updated to match this. I think
the partial changes were done in MATH-701, more specifically, in commit
[1197626] (and related commit [1197716]).
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