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  1. Commons Math
  2. MATH-720

RandomDataImpl uses both JDKRandomGenerator and Well19937c, while contract/javadoc only specifies Well19937c.

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Details

    • Bug
    • Status: Closed
    • Major
    • Resolution: Fixed
    • None
    • 3.0

    Description

      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:

      5
      4
      

      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]).

      Attachments

        1. TestRandom.java
          0.5 kB
          Dennis Hendriks

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              dhendriks Dennis Hendriks
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