improve randomness in pseudo scorer

matsim-scenarios · Dec 1, 2024 · f488192 · f488192
1 parent 0db7c42
commit f488192
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Showing 2 changed files with 26 additions and 5 deletions.
diff --git a/src/main/java/org/matsim/run/scoring/IndividualPersonScoringParameters.java b/src/main/java/org/matsim/run/scoring/IndividualPersonScoringParameters.java
@@ -90,7 +90,15 @@ public IndividualPersonScoringParameters(Scenario scenario) {
 		this.globalAvgIncome = computeAvgIncome(scenario.getPopulation());
 		this.categories = Category.fromConfigParams(this.scoring.getScoringParameters());
 		this.cache = new IdMap<>(Person.class, scenario.getPopulation().getPersons().size());
-		this.rnd = ThreadLocal.withInitial(() -> new Context(scenario.getConfig().global().getRandomSeed()));
+
+		// Create uncorrelated seed from the global seed
+		SplittableRandom rnd = new SplittableRandom(scenario.getConfig().global().getRandomSeed());
+		for (int i = 0; i < rnd.nextInt(); i++) {
+			rnd.nextLong();
+		}
+
+		byte[] seed = Longs.toByteArray(rnd.nextLong());
+		this.rnd = ThreadLocal.withInitial(() -> new Context(seed));
 	}
 
 	static DistanceGroup[] calcDistanceGroups(List<Integer> dists, DoubleList distUtils) {
@@ -338,11 +346,10 @@ private void addDeltaParams(Context ctx, DistanceGroupModeUtilityParameters.Delt
 	 */
 	private record Context(NormalDistribution normal, TruncatedNormalDistribution tn, byte[] seed, RestorableUniformRandomProvider rnd) {
 
-		Context(long seed) {
+		Context(byte[] seed) {
 			this(NormalDistribution.of(0, 1),
 				TruncatedNormalDistribution.of(0, 1, 0, Double.POSITIVE_INFINITY),
-				// Feed seed into random number generator
-				Longs.toByteArray(new SplittableRandom(seed).nextLong()),
+				seed,
 				RandomSource.KISS.create());
 		}
 
@@ -361,6 +368,11 @@ void setSeed(Person p) {
 			System.arraycopy(person, 0, state, 8, Math.min(person.length, 12));
 
 			rnd.restoreState(new RandomProviderDefaultState(state));
+
+			// Warm up the generator
+			for (int i = 0; i < 100; i++) {
+				rnd.nextLong();
+			}
 		}
 	}
 }
diff --git a/src/main/java/org/matsim/run/scoring/PseudoRandomScorer.java b/src/main/java/org/matsim/run/scoring/PseudoRandomScorer.java
@@ -11,6 +11,8 @@
 import org.matsim.core.config.Config;
 import org.matsim.core.config.ConfigUtils;
 
+import java.util.SplittableRandom;
+
 /**
  * Computes pseudo random errors (epsilons), which are frozen for certain choice situations, thus representing the unobserved heterogeneity.
  */
@@ -29,9 +31,16 @@ public final class PseudoRandomScorer {
 	@Inject
 	public PseudoRandomScorer(PseudoRandomTripError tripScore, Config config) {
 		this.tripScore = tripScore;
-		this.seed = config.global().getRandomSeed();
 		this.scale = ConfigUtils.addOrGetModule(config, AdvancedScoringConfigGroup.class).pseudoRamdomScale;
 		this.distribution = ConfigUtils.addOrGetModule(config, AdvancedScoringConfigGroup.class).pseudoRandomDistribution;
+
+		SplittableRandom rnd = new SplittableRandom(config.global().getRandomSeed());
+		for (int i = 0; i < WARMUP_ITERATIONS; i++) {
+			rnd.nextDouble();
+		}
+
+		// Create a random seed from the global one
+		this.seed = rnd.nextLong();
 	}
 
 	/**