Bug fix in simulator: in DTMCs with local nondeterminism, random transitions can be wrongly chosen due to the distributions not being normalised.

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@9352 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/simulator/SimulatorEngine.java

@@ -299,8 +299,16 @@ public class SimulatorEngine extends PrismComponent
 			return false;
 		//throw new PrismException("Deadlock found at state " + path.getCurrentState().toString(modulesFile));
 
+		TransitionList.Ref ref;
 		switch (modelType) {
 		case DTMC:
+			// Pick a random number to determine choice/transition
+			d = rng.randomUnifDouble();
+			ref = transitions.new Ref();
+			transitions.getChoiceIndexByProbabilitySum(d, ref);
+			// Execute
+			executeTransition(ref.i, ref.offset, -1);
+			break;
 		case MDP:
 			// Pick a random choice
 			i = rng.randomUnifInt(numChoices);
@@ -316,7 +324,7 @@ public class SimulatorEngine extends PrismComponent
 			r = transitions.getProbabilitySum();
 			// Pick a random number to determine choice/transition
 			d = rng.randomUnifDouble(r);
-			TransitionList.Ref ref = transitions.new Ref();
+			ref = transitions.new Ref();
 			transitions.getChoiceIndexByProbabilitySum(d, ref);
 			// Execute
 			executeTimedTransition(ref.i, ref.offset, rng.randomExpDouble(r), -1);

prism/src/simulator/TransitionList.java

@@ -158,10 +158,9 @@ public class TransitionList
 	// Random selection of a choice 
 
 	/**
-	 * Get a reference to a transition according to a total probability (rate) sum, x.
-	 * i.e.the first transition for which the sum of probabilities of that and all prior
-	 * transitions (across all choices) exceeds x. Really, this is designed for the case
-	 * where these are rates, rather than probabilities.
+	 * Get a reference to a transition according to a total probability (or rate) sum, x.
+	 * i.e.the first transition for which the sum of probabilities/rates of that and all prior
+	 * transitions (across all choices) exceeds x.
 	 * @param x Probability (or rate) sum
 	 * @param ref Empty transition reference to store result
 	 */