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https://issues.apache.org/jira/browse/RNG-97?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16827748#comment-16827748
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Alex D Herbert commented on RNG-97:
-----------------------------------
All valid points.
Having formalised the ideas from the dev mailing list to form this ticket I am
not sure this is the best implementation. The need to create a series by
chaining the return values has resulted in a helper method in RandomSource to
create a series of known length. This does not support creating an open ended
series of unknown size (as if a Java 8 function
Supplier<UniformRandomProvider>) or creating two series from the same parent
without extra code to regain the reference to the terminal jump point.
I'll take the discussion back to the mailing list.
> JumpableUniformRandomProvider
> -----------------------------
>
> Key: RNG-97
> URL: https://issues.apache.org/jira/browse/RNG-97
> Project: Commons RNG
> Issue Type: New Feature
> Components: client-api, core
> Affects Versions: 1.3
> Reporter: Alex D Herbert
> Assignee: Alex D Herbert
> Priority: Major
> Fix For: 1.3
>
>
> A feature of random number generators is their internal state is updated for
> every generation of a new random number. This is a single step. Some
> generators have the ability to compute the update to the state that is
> required to advance *{{n}}* steps. This is a jump. This can be supported
> using a new interface:
> {code:java}
> /**
> * Applies to generators that can be advanced a large number of
> * steps of the output sequence in a single operation.
> */
> public interface JumpableUniformRandomProvider
> extends UniformRandomProvider {
> /**
> * Creates a copy of the UniformRandomProvider and advances the
> * state of the copy. The state of the current instance is not altered.
> * The state of the copy will be advanced an equivalent of {@code n}
> * sequential calls to a method that updates the state of the provider.
> *
> * @return the copy with an advanced state
> */
> JumpableUniformRandomProvider jump();
> }
> {code}
> A suggestion for how to document an implementation is:
> {code:java}
> public class JumpableRNG implements JumpableUniformRandomProvider {
> /**
> * {@inheritDoc}
> *
> * <p>The jump size {@code n} is the equivalent of
> <pre>2<sup>32</sup></pre>
> * calls to {@link UniformRandomProvider#nextLong() nextLong()}.</p>
> */
> @Override
> public JumpableUniformRandomProvider jump() {
> return ...;
> }
> // etc.
> }
> {code}
> Notes on the interface:
> * A copy is returned
> * The original is not altered and so multiple calls to jump will return the
> same generator with an advanced state
> The intended use case is to create multiple copies of a RNG that will not
> overlap in sequence for use in parallel computations. A helper method can be
> added to {{RandomSource}} to facilitate this:
> {code:java}
> /**
> * Create a series of {@code n} generators by jumping from the source
> generator
> * {@code n} times. The resulting set of generators can be used in parallel
> * computations with a guarantee of no sequence overlap for at least the
> * length of the jump distance.
> *
> * <p>Note: The source generator state is not affected. Reuse of this
> * generator may overlap with output from the jump series.</p>
> *
> * @param source The source generator.
> * @param n The size of the series.
> */
> public static UniformRandomProvider[] createJumpSeries(
> JumpableUniformRandomProvider source, int n) {
> if (n <= 0) {
> throw new IllegalArgumentException("Size must be strictly positive");
> }
> final UniformRandomProvider[] rngs = new UniformRandomProvider[n];
> for (int i = 0; i < n; i++) {
> source = source.jump();
> // Option to wrap the JumpableUniformRandomProvider to
> // restrict to the functionality of UniformRandomProvider
> rngs[i] = source;
> }
> return rngs;
> }
> {code}
> Note: There is the possibility to wrap the jumped RNGs to restrict their
> functionality to UniformRandomProvider (or RestorableUniformRandomProvider).
> This prevents any of the series from being jumped again.
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