MDP reachability in explicit engine: do not do numerical solution unless needed.

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@6912 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/explicit/MDPModelChecker.java

@@ -408,7 +408,8 @@ public class MDPModelChecker extends ProbModelChecker
 			}
 		}
 
-		// Compute probabilities
+		// Compute probabilities (if needed)
+		if (numYes + numNo < n) {
 			switch (mdpSolnMethod) {
 			case VALUE_ITERATION:
 				res = computeReachProbsValIter(mdp, no, yes, min, init, known, strat);
@@ -425,6 +426,11 @@ public class MDPModelChecker extends ProbModelChecker
 			default:
 				throw new PrismException("Unknown MDP solution method " + mdpSolnMethod.fullName());
 			}
+		} else {
+			res = new ModelCheckerResult();
+			res.soln = Utils.bitsetToDoubleArray(yes, n);
+			return res;
+		}
 
 		// Finished probabilistic reachability
 		timer = System.currentTimeMillis() - timer;