Implemented agent which chooses to play winning, losing or random moves by solving a simplified MDP model of the game using policy iteration.

Portions of MDP/solver code by Ciaran O'Reilly and Ravi Mohan used under MIT license.

test/aima/core/probability/mdp/PolicyIterationTest.java

@@ -0,0 +1,80 @@
+package aima.core.probability.mdp;
+
+import java.util.Map;
+
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import aima.core.environment.cellworld.Cell;
+import aima.core.environment.cellworld.CellWorld;
+import aima.core.environment.cellworld.CellWorldAction;
+import aima.core.environment.cellworld.CellWorldFactory;
+import aima.core.environment.gridworld.GridCell;
+import aima.core.environment.gridworld.GridWorld;
+import aima.core.environment.gridworld.GridWorldAction;
+import aima.core.environment.gridworld.GridWorldFactory;
+import aima.core.probability.example.MDPFactory;
+import aima.core.probability.mdp.MarkovDecisionProcess;
+import aima.core.probability.mdp.impl.ModifiedPolicyEvaluation;
+import aima.core.probability.mdp.search.PolicyIteration;
+import aima.core.probability.mdp.search.ValueIteration;
+
+/**
+ * @author Ravi Mohan
+ * @author Ciaran O'Reilly
+ * 
+ */
+public class PolicyIterationTest {
+	public static final double DELTA_THRESHOLD = 1e-3;
+
+	private GridWorld<Double> gw = null;
+	private MarkovDecisionProcess<GridCell<Double>, GridWorldAction> mdp = null;	
+	private PolicyIteration<GridCell<Double>, GridWorldAction> pi = null;
+
+	final int maxTiles = 6;
+	final int maxScore = 10;
+	
+	@Before
+	public void setUp() {
+		//take 10 turns to place 6 tiles
+		double defaultPenalty = -0.04;
+		
+		gw = GridWorldFactory.createGridWorldForTileGame(maxTiles,maxScore,defaultPenalty);
+		mdp = MDPFactory.createMDPForTileGame(gw, maxTiles, maxScore);
+				
+		//gamma = 1.0
+		PolicyEvaluation<GridCell<Double>,GridWorldAction> pe = new ModifiedPolicyEvaluation<GridCell<Double>, GridWorldAction>(100,0.9);
+		pi = new PolicyIteration<GridCell<Double>, GridWorldAction>(pe);
+	}
+
+	@Test
+	public void testPolicyIterationForTileGame() {
+		Policy<GridCell<Double>, GridWorldAction> policy = pi.policyIteration(mdp);
+
+		for (int j = maxScore; j >= 1; j--) {
+			StringBuilder sb = new StringBuilder();
+			for (int i = 1; i <= maxTiles; i++) {
+				sb.append(policy.action(gw.getCellAt(i, j)));
+				sb.append(" ");
+			}
+			System.out.println(sb.toString());
+		}
+		
+		//Assert.assertEquals(0.705, U.get(gw.getCellAt(1, 1)), DELTA_THRESHOLD);
+		/*
+		Assert.assertEquals(0.762, U.get(cw1.getCellAt(1, 2)), DELTA_THRESHOLD);
+		Assert.assertEquals(0.812, U.get(cw1.getCellAt(1, 3)), DELTA_THRESHOLD);
+
+		Assert.assertEquals(0.655, U.get(cw1.getCellAt(2, 1)), DELTA_THRESHOLD);
+		Assert.assertEquals(0.868, U.get(cw1.getCellAt(2, 3)), DELTA_THRESHOLD);
+
+		Assert.assertEquals(0.611, U.get(cw1.getCellAt(3, 1)), DELTA_THRESHOLD);
+		Assert.assertEquals(0.660, U.get(cw1.getCellAt(3, 2)), DELTA_THRESHOLD);
+		Assert.assertEquals(0.918, U.get(cw1.getCellAt(3, 3)), DELTA_THRESHOLD);
+
+		Assert.assertEquals(0.388, U.get(cw1.getCellAt(4, 1)), DELTA_THRESHOLD);
+		Assert.assertEquals(-1.0, U.get(cw1.getCellAt(4, 2)), DELTA_THRESHOLD);
+		Assert.assertEquals(1.0, U.get(cw1.getCellAt(4, 3)), DELTA_THRESHOLD);*/
+	}
+}