Develop Reference

A* Pathfinding really slow

I have an A* pathfinding algorithm that I've used for a Spigot plugin which worked fine. I then added a requirements system so it won't try and pathfind through places it shouldn't. Now it seems REALLY slow, and it looks like it has nothing to do with the requirements code itself, and more to do with the algorithm having many more incorrect paths when calculating. I seem to be getting 1500ms+ on this, which is definitely not good xD
Here is the pathfinder code:
public Path calculate(PathfinderGoal goal, PathScorer scorer, List<PathRequirement> requirements, int maxNodes) {
PathNode start = toNode(npc.getLocation());
PathNode end = toNode(goal.getLocation());
List<PathNode> open = new ArrayList<>() {{ add(start); }};
List<PathNode> navigated = new ArrayList<>();
start.setF(scorer.computeCost(start, end));
Timer timer = new Timer().start();
while (!open.isEmpty()) {
PathNode current = null;
for (PathNode node : open) {
if (current == null || node.getH() < current.getH()) {
current = node;
}
}
if (scorer.computeCost(current, end) < 1 || (navigated.size() >= maxNodes && maxNodes != -1)) {
navigated.add(navigated.size() < maxNodes ? end : current);
return reconstruct(navigated, navigated.size() - 1);
}
open.remove(current);
current.close();
for (PathNode node : current.getNeighbors()) {
if (node.isClosed()) {
continue;
}
double tentG = current.getG() + scorer.computeCost(current, node);
if (!open.contains(node) || tentG < node.getG()) {
boolean requirementsMet = true;
for (PathRequirement requirement : requirements) {
requirement.setNavigated(navigated);
if (!navigated.isEmpty() && !requirement.canMoveToNewNode(navigated.get(navigated.size() - 1), node)) {
requirementsMet = false;
break;
}
}
if (!navigated.contains(current)) {
navigated.add(current);
}
node.setG(tentG);
node.setH(scorer.computeCost(node, end));
node.setF(tentG + node.getH());
if (!open.contains(node) && requirementsMet) {
open.add(node);
}
}
}
Bukkit.broadcastMessage("Open Set Size: " + open.size());
Bukkit.broadcastMessage(timer.stop() + "ms");
}
return null;
}
private Path reconstruct(List<PathNode> navigated, int index) {
final PathNode current = navigated.get(index);
Path withCurrent = new Path(new ArrayList<>() {{ add(current); }});
if (index > 0 && navigated.contains(current)) {
return reconstruct(navigated, index - 1).append(withCurrent);
}
return withCurrent;
}
And here is the PathNode class:
public PathNode(Pathfinder pathfinder, int x, int y, int z) {
this.pathfinder = pathfinder;
this.x = x;
this.y = y;
this.z = z;
}
#Override
public boolean equals(Object other) {
if (!(other instanceof PathNode otherNode)) {
return false;
}
return otherNode.x == x && otherNode.y == y && otherNode.z == z;
}
public List<PathNode> getNeighbors() {
return new ArrayList<>() {
{
for (int x = -1; x <= 1; x++) {
for (int y = -1; y <= 1; y++) {
for (int z = -1; z <= 1; z++) {
add(new PathNode(pathfinder, PathNode.this.x + x, PathNode.this.y + y, PathNode.this.z + z));
}
}
}
}
};
}
public Location getLocation() {
return new Location(pathfinder.getNPC().getLocation().getWorld(), x, y, z);
}
public double getF() {
return F;
}
public void setF(double f) {
this.F = f;
}
public double getG() {
return G;
}
public void setG(double g) {
this.G = g;
}
public double getH() {
return H;
}
public void setH(double h) {
this.H = h;
}
public boolean isClosed() {
return closed;
}
public void close() {
this.closed = true;
}
Valid Requirements Class:
public class ValidPathRequirement extends PathRequirement {
#Override
public boolean canMoveToNewNode(PathNode from, PathNode to) {
Block fromBlock = from.getLocation().getBlock();
Block toBlock = to.getLocation().getBlock();
boolean validHeight = toBlock.getType().isAir() && toBlock.getRelative(BlockFace.UP).getType().isAir(); // checks if is player height
boolean validGround = toBlock.getRelative(BlockFace.DOWN).getType().isSolid(); // is there a block underneath that they can stand on?
boolean validFromPrev = toBlock.getLocation().subtract(fromBlock.getLocation()).getY() <= 1; // is it max one block higher than the last one?
// is this one causing issues?
Location fromLocDist = from.getLocation().clone();
Location toLocDist = to.getLocation().clone();
toLocDist.setY(fromLocDist.getY());
boolean validDistance = fromLocDist.distance(toLocDist) <= 1;
return validHeight && validGround && validFromPrev;
}
}

Without looking at the rest of the algorithm, the first thing that stands out is that your data structures are incorrect. The "open" list needs to be a Priority Queue, and "closed" (or "navigated") should be a set.

A* algorithm completes but returns suboptimal path

The algorithm:
Uses a PQ that supports change priority operations.
Assume all the ADTs work correctly.
Example problem: Find the shortest path of operations to get from integer x to integer y using the following operations and weights; add/subtract 1 : 1, multiply/divide by 2 : 5, square : 10.
Tested against other types of graphs and inputs, sometimes it gets the shortest path, sometimes it gets a suboptimal, sometimes it times out.
import java.util.*;
/**
* Represents a graph of vertices.
*/
public interface AStarGraph<Vertex> {
List<WeightedEdge<Vertex>> neighbors(Vertex v);
double estimatedDistanceToGoal(Vertex s, Vertex goal);
}
public interface ShortestPathsSolver<Vertex> {
SolverOutcome outcome();
List<Vertex> solution();
double solutionWeight();
int numStatesExplored();
double explorationTime();
}
public interface ExtrinsicMinPQ<T> {
/* Inserts an item with the given priority value. */
void add(T item, double priority);
/* Returns true if the PQ contains the given item. */
boolean contains(T item);
/* Returns the minimum item. */
T getSmallest();
/* Removes and returns the minimum item. */
T removeSmallest();
/* Changes the priority of the given item. Behavior undefined if the item doesn't exist. */
void changePriority(T item, double priority);
/* Returns the number of itemToPriority in the PQ. */
int size();
}
public enum SolverOutcome {
SOLVED, TIMEOUT, UNSOLVABLE
}
public class ArrayHeapMinPQ<T> implements ExtrinsicMinPQ<T> {
private ArrayList<PriorityNode> heap;
int count;
private HashMap<T, PriorityNode> items;
public ArrayHeapMinPQ() {
heap = new ArrayList<>();
heap.add(0, new PriorityNode(null, Double.NEGATIVE_INFINITY));
count = 0; // For convenient math
items = new HashMap<>();
}
#Override
public void add(T item, double priority) {
if(contains(item)){
throw new IllegalArgumentException();
}
PriorityNode pn = new PriorityNode(item, priority);
if(count == 0){
heap.add(1, pn);
count++;
}else{
heap.add(count+1, pn);
swim(count+1);
count++;
}
items.put(item, pn);
}
private void swap(int i, int j){
Collections.swap(heap, i, j);
}
private void swim(int i){
while(i > 1){
PriorityNode cur = heap.get(i);
if((cur.compareTo(heap.get(i/2)) >= 0)){
break;
}
swap(i, i/2);
i = i/2;
}
}
private void sink(int k){
while (2*k <= size()-1) {
if(2*k+1 <= size()-1) {
if (heap.get(2 * k).compareTo(heap.get(2 * k + 1)) < 0) {
if (heap.get(k).compareTo(heap.get(2 * k)) > 0) {
swap(k, 2 * k);
k = 2 * k;
continue;
}
} else if(heap.get(k).compareTo(heap.get(2*k+1)) > 0){
swap(2*k+1, k);
k = 2*k +1;
continue;}
}
else if (heap.get(k).compareTo(heap.get(2 * k)) > 0) {
swap(k, 2 * k);
k = 2 * k;
continue;}
break;
}
}
#Override
public int size(){
return heap.size();
}
public PriorityNode getRoot(){
return heap.get(1);
}
#Override
public boolean contains(T item) {
return items.containsKey(item);}
#Override
public T getSmallest() {
if(heap.size() == 0){
throw new NoSuchElementException();
}
return getRoot().getItem();
}
#Override
public T removeSmallest() {
if(heap.size() == 1){
throw new NoSuchElementException();
}
T item = heap.get(1).item;
swap(1, size()-1);
heap.remove(size()-1);
if(size() > 1){
sink(1);
}
items.remove(item);
count--;
return item;
}
public boolean isEmpty(){
return heap.size() == 1;
}
public int getCount() {
return count;
}
#Override
public void changePriority(T T, double priority) {
if(heap.size() == 0){
throw new NoSuchElementException();
}
PriorityNode tochange = items.get(T);
double prioritysearch = tochange.getPriority();
double currprior = getRoot().getPriority();
int left = 0;
int right = 0;
if((prioritysearch != currprior)){
if (currprior > prioritysearch){
add(T, priority);
return;
}
left = heapTraverse(prioritysearch, tochange, 2);
right = heapTraverse(prioritysearch, tochange, 3);
}
if(left == -1 && right == -1){
throw new NoSuchElementException();
}
else if(left > 0){
PriorityNode toChange = heap.get(left);
toChange.setPriority(priority);
if(priority < heap.get(left/2).getPriority()){
swim(left);
}else
sink(left);
}
else {
PriorityNode toChange = heap.get(right);
toChange.setPriority(priority);
if (priority < heap.get(right / 2).getPriority()) {
swim(right);
} else
sink(right);
}
}
private int heapTraverse(double priority, PriorityNode node, int index){
if(index > heap.size()-1){
return -1;
}
PriorityNode curr = heap.get(index);
double currprior = curr.getPriority();
if(currprior == priority && node.equals(curr)){
return index;
} else if(currprior > priority){
return -1;
}else{
if(heapTraverse(priority, node, index*2) == -1){
return heapTraverse(priority, node, index*2 +1);}
else {return heapTraverse(priority, node, index*2);}
}
}
private class PriorityNode implements Comparable<PriorityNode> {
private T item;
private double priority;
PriorityNode(T e, double p) {
this.item = e;
this.priority = p;
}
T getItem() {
return item;
}
double getPriority() {
return priority;
}
void setPriority(double priority) {
this.priority = priority;
}
#Override
public int compareTo(PriorityNode other) {
if (other == null) {
return -1;
}
return Double.compare(this.getPriority(), other.getPriority());
}
#Override
public boolean equals(Object o) {
if( o == null) {
throw new NullPointerException();
}
if (o.getClass() != this.getClass()) {
return false;
} else {
return ((PriorityNode) o).getItem().equals(getItem());
}
}
#Override
public int hashCode() {
return item.hashCode();
}
}
public class WeightedEdge<Vertex> {
private Vertex v;
private Vertex w;
private double weight;
public WeightedEdge(Vertex v, Vertex w, double weight) {
this.v = v;
this.w = w;
this.weight = weight;
}
public Vertex from() {
return v;
}
public Vertex to() {
return w;
}
public double weight() {
return weight;
}
}
public class SolutionPrinter {
/** Summarizes the result of the search made by this solver without actually
* printing the solution itself (if any).
*/
public static <Vertex> void summarizeOutcome(ShortestPathsSolver<Vertex> solver) {
summarizeSolution(solver, "", false);
}
/** Summarizes the result of the search made by this solver and also
* prints each vertex of the solution, connected by the given delimiter,
* e.g. delimiter = "," would return all states separated by commas.
*/
public static <Vertex> void summarizeSolution(ShortestPathsSolver<Vertex> solver,
String delimiter) {
summarizeSolution(solver, delimiter, true);
}
private static <Vertex> String solutionString(ShortestPathsSolver<Vertex> solver,
String delimiter) {
List<String> solutionVertices = new ArrayList<>();
for (Vertex v : solver.solution()) {
solutionVertices.add(v.toString());
}
return String.join(delimiter, solutionVertices);
}
private static <Vertex> void summarizeSolution(ShortestPathsSolver<Vertex> solver,
String delimiter, boolean printSolution) {
System.out.println("Total states explored in " + solver.explorationTime()
+ "s: " + solver.numStatesExplored());
if (solver.outcome() == SolverOutcome.SOLVED) {
List<Vertex> solution = solver.solution();
System.out.println("Search was successful.");
System.out.println("Solution was of length " + solution.size()
+ ", and had total weight " + solver.solutionWeight() + ":");
if (printSolution) {
System.out.println(solutionString(solver, delimiter));
}
} else if (solver.outcome() == SolverOutcome.TIMEOUT) {
System.out.println("Search timed out, considered " + solver.numStatesExplored()
+ " vertices before timing out.");
} else { // (solver.outcome() == SolverOutcome.UNSOLVABLE)
System.out.println("Search determined that the goal is unreachable from source.");
}
}
}
public class AStarSolver implements ShortestPathsSolver {
private final AStarGraph<Vertex> graph;
private Vertex source;
private Vertex dest;
private SolverOutcome result;
private HashMap<Vertex, Double> distTo = new HashMap<>();
private ArrayHeapMinPQ<Vertex> fringe = new ArrayHeapMinPQ<>();
private HashMap<Vertex, WeightedEdge<Vertex>> edgeTo = new HashMap<>(); // answers the question which vertex to ge to this vertex
private double solutionweight;
private List<Vertex> solution;
private ArrayList<Vertex> marked = new ArrayList<>();
private double timetosolve;
private int numofstates = 0;
public AStarSolver(AStarGraph<Vertex> input, Vertex start, Vertex end, double timeout ){
graph = input;
source = start;
dest = end;
if(start.equals(end)){
solutionweight = 0;
solution = List.of(start);
result = SolverOutcome.SOLVED;
numofstates = 0;
timetosolve = 0;
return;
}
fringe.add(start, 0.0);
distTo.put(start, 0.0);
while (!fringe.isEmpty()) {
Vertex src = fringe.removeSmallest();
numofstates++;
marked.add(src);
List<WeightedEdge<Vertex>> neighbors = graph.neighbors(src);
for(WeightedEdge<Vertex> e: neighbors){
double heur = graph.estimatedDistanceToGoal(e.to(), dest);
if ((heur == Double.POSITIVE_INFINITY || marked.contains(e.to())) && !e.to().equals(dest)) {
continue;
}
double distFr = distTo.get(e.from()) + e.weight();
if(!distTo.containsKey(e.to())){
distTo.put(e.to(), distFr);
}
if (!fringe.contains(e.to())) {
fringe.add(e.to(), distFr + heur);
edgeTo.put(e.to(), e);
}
if (distTo.get(e.to()) > distFr) {
fringe.changePriority(e.to(), heur + distFr);
edgeTo.put(e.to(), e);
distTo.put(e.to(), distFr);
}
if (e.to().equals(dest)) {
solutionweight = distTo.get(e.to());
solution = pathTracer(e);
timetosolve = sw.elapsedTime();
result = SolverOutcome.SOLVED;
return;
}
if (e.to().equals(dest)) {
solutionweight = distTo.get(e.to());
solution = pathTracer(e);
timetosolve = sw.elapsedTime();
result = SolverOutcome.SOLVED;
return;
}
}
if (timeout < sw.elapsedTime()){
result = SolverOutcome.TIMEOUT;
return;
}
}
result = SolverOutcome.UNSOLVABLE;
solution = List.of();
}
private List<Vertex> pathTracer(WeightedEdge<Vertex> e) {
ArrayList<Vertex> path = new ArrayList<>();
path.add(e.to());
path.add(e.from());
while (!e.from().equals(source)) {
e = edgeTo.get(e.from());
path.add(e.from());
}
Collections.reverse(path);
return path;
}
#Override
public SolverOutcome outcome() {
return result;
}
#Override
public List solution() {
return solution;
}
#Override
public double solutionWeight() {
return solutionweight;
}
#Override
public int numStatesExplored() {
return numofstates;
}
#Override
public double explorationTime() {
return timetosolve;
}
public class IntegerHopGraph implements AStarGraph<Integer> {
#Override
public List<WeightedEdge<Integer>> neighbors(Integer v) {
ArrayList<WeightedEdge<Integer>> neighbors = new ArrayList<>();
neighbors.add(new WeightedEdge<>(v, v * v, 10));
neighbors.add(new WeightedEdge<>(v, v * 2, 5));
neighbors.add(new WeightedEdge<>(v, v / 2, 5));
neighbors.add(new WeightedEdge<>(v, v - 1, 1));
neighbors.add(new WeightedEdge<>(v, v + 1, 1));
return neighbors;
}
#Override
public double estimatedDistanceToGoal(Integer s, Integer goal) {
// possibly fun challenge: Try to find an admissible heuristic that
// speeds up your search. This is tough!
return 0;
}
}
public class DemoIntegerHopPuzzleSolution {
public static void main(String[] args) {
int start = 17;
int goal = 111;
IntegerHopGraph ahg = new IntegerHopGraph();
ShortestPathsSolver<Integer> solver = new AStarSolver<>(ahg, start, goal, 10);
SolutionPrinter.summarizeSolution(solver, " => ");
}
}
}
To get from x = 11, to y = 117 the algorithm gives this result:
Total states explored in 0.019s: 110
Search was successful.
Solution was of length 7, and had total weight 19.0:
17 => 16 => 15 => 225 => 224 => 223 => 111
The correct result should is:
Total states explored in 0.018s: 338 <--- may vary.
Search was successful.
Solution was of length 6, and had total weight 18.0:
17 => 16 => 15 => 225 => 112 => 111

Thanks for all the help guys but I figured it out. My algorithm terminates prematurely. It stops when it sees the finish, not when it is on the top of the heap like it should.

Tic Tac Toe: All states get returned as best moves

I am working on building the game of Tic Tac Toe. Please find below the description of the classes used.
Game:: The main class. This class will initiate the multiplayer mode.
Board: This class sets the board configurations.
Computer: This class comprises of the minimax algorithm.
BoardState: This class comprises of the Board Object, along with the last x and y coordinates which were used to generate the board
configuration.
State: This class comprises of the score and the x and y coordinates that that will lead to that score in the game.
Context
Working on DFS here.
Exploring the whole tree works fine.
The game is set in such a way that the user is prompted to play first.
The user will put x and y co ordinates in the game.Coordinates are between 0 to 2. The Play of the player is marked as 1
The response from the computer is 2, which the algorithm decides. Th algorithm will determine the best possible coordinates to play and then play 2 on the position.
One of the winning configurations for Player is :
Player wins through diagonal
121
112
221
One of the winning configuration for AI is:
222
121
211
AI wins Horizontal
Problem
All the states give the max score.
Essentially, when you start the game in your system, you will find that since all states are given the max score, the computer looks to play sequentially.
As in if you put at (00), the computer plays at (01) and if you play at (02), the computer will play at (10)
I have been trying to debug it for a long time now. I believe, I may be messing up something with the scoring function. Or there could be a bug in the base recursion steps. Moreover, I don't think immutability among classes could cause problems as I have been recreating/creating new objects everywhere.
I understand, this might not be the best context I could give, but it would be a great help if you guys could help me figure out where exactly is it going wrong and what could I do to fix it. Answers through code/logic used would be highly appreciated. Thanks!
Game Class
import java.io.Console;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;
public class Game {
static int player1 = 1;
static int player2 = 2;
public static void main(String[] args) {
// TODO Auto-generated method stub
//
//PLays Game
playGame();
/* Test Use Case
ArrayList<Board> ar = new ArrayList<Board>();
Board b = new Board();
b.setVal(0,0,1);
b.setVal(0,1,1);
b.setVal(0,2,2);
b.setVal(1,0,2);
b.setVal(1,1,2);
b.setVal(2,0,1);
b.setVal(2,1,1);
b.display();
Computer comp = new Computer();
State x = comp.getMoves(b, 2);
*/
}
private static void playGame() {
// TODO Auto-generated method stub
Board b = new Board();
Computer comp = new Computer();
while(true)
{
if(b.isBoardFull())
{
System.out.println("Game Drawn");
break;
}
b.display();
int[] pmove = getPlayerMove(b);
b.setVal(pmove[0],pmove[1], player1);
if(b.isVictoriousConfig(player1))
{
System.out.println("Player 1 Wins");
break;
}
if(b.isBoardFull())
{
System.out.println("Game Drawn");
break;
}
b.display();
System.out.println("Computer Moves");
/*For Random Play
* int[] cmove = comp.computeMove(b);
*/
Computer compu = new Computer();
State s = compu.getMoves(b, 2);
int[] cmove = new int[2];
cmove[0] = s.x;
cmove[1] = s.y;
b.setVal(cmove[0],cmove[1], player2);
if(b.isVictoriousConfig(player2))
{
System.out.println("Computer Wins");
break;
}
}
System.out.println("Game Over");
}
//Gets Player Move. Basic Checks on whether the move is a valud move or not.
private static int[] getPlayerMove(Board b) {
// TODO Auto-generated method stub
int[] playerMove = new int[2];
System.out.println("You Play");
while(true)
{
#SuppressWarnings("resource")
Scanner reader = new Scanner(System.in); // Reading from System.in
System.out.println("Enter X Position: ");
while(true)
{
playerMove[0] = reader.nextInt(); // Scans the next token of the input as an int.
if(playerMove[0] >2)
{
System.out.println("Incorrect Position");
}
else
{
break;
}
}
System.out.println("Enter Y Position: ");
while(true)
{
playerMove[1] = reader.nextInt(); // Scans the next token of the input as an int.
if(playerMove[1] >2)
{
System.out.println("Incorrect Position");
}
else
{
break;
}
}
System.out.println("You entered positions: X is " + playerMove[0] + " and Y is " + playerMove[1] );
if(!b.isPosOccupied(playerMove[0], playerMove[1]))
{
break;
}
System.out.println("Incorrect Move. PLease try again");
}
return playerMove;
}
}
Board Class
import java.util.Arrays;
public class Board {
// Defines Board Configuration
private final int[][] data ;
public Board()
{
data = new int[3][3];
for(int i=0;i<data.length;i++ )
{
for(int j=0;j<data.length;j++ )
{
data[i][j] = 0;
}
}
}
//Displays Current State of the board
public void display()
{
System.out.println("Board");
for(int i = 0; i< data.length;i++)
{
for(int j = 0; j< data.length;j++)
{
System.out.print(data[i][j] + " ");
}
System.out.println();
}
}
// Gets the Value on a specific board configuration
public int getVal(int i, int j)
{
return data[i][j];
}
//Sets the value to a particular board location
public void setVal(int i, int j,int val)
{
data[i][j] = val;
}
public boolean isBoardFull()
{
for(int i=0;i< data.length ; i++)
{
for(int j=0;j< data.length ;j++)
{
if(data[i][j] == 0)
return false;
}
}
return true;
}
public boolean isVictoriousConfig(int player)
{
//Noting down victory rules
//Horizontal Victory
if ( (data[0][0] != 0) && ((data[0][0] == data [0][1]) && (data[0][1] == data [0][2]) && (data[0][2] == player)))
return true;
if ((data[1][0] != 0) && ((data[1][0] == data [1][1]) && (data[1][1] == data [1][2]) && (data[1][2] == player)))
return true;
if ((data[2][0] != 0) && ((data[2][0] == data [2][1]) && (data[2][1] == data [2][2]) && (data[2][2] == player)))
return true;
//Vertical Victory
if ( (data[0][0] != 0) && ((data[0][0] == data [1][0]) && (data[1][0] == data [2][0]) && (data[2][0] == player)))
return true;
if ((data[0][1] != 0) && ((data[0][1] == data [1][1]) && (data[1][1] == data [2][1]) && (data[2][1] == player)))
return true;
if ((data[0][2] != 0) && ((data[0][2] == data [1][2]) && (data[1][2] == data [2][2]) && (data[2][2] == player)))
return true;
//Diagonal Victory
if ( (data[0][0] != 0) && ((data[0][0] == data [1][1]) && (data[1][1] == data [2][2]) && (data[2][2] == player)))
return true;
if ( (data[0][2] != 0) && ((data[0][2] == data [1][1]) && (data[1][1] == data [2][0]) && (data[2][0] == player)))
return true;
//If none of the victory rules are met. No one has won just yet ;)
return false;
}
public boolean isPosOccupied(int i, int j)
{
if(data[i][j] != 0)
{
return true;
}
return false;
}
public Board(int[][] x)
{
this.data = Arrays.copyOf(x, x.length);
}
}
Board State
public class BoardState {
final Board br;
final int x ;
final int y;
public BoardState(Board b, int posX, int posY)
{
br = b;
x = posX;
y = posY;
}
}
State
public class State {
final int s;
final int x;
final int y;
public State(int score, int posX, int posY)
{
s = score;
x = posX;
y = posY;
}
}
Computer
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Random;
import java.util.Set;
public class Computer {
int[] pos = new int[2];
static int player2 = 2;
static int player1 = 1;
ArrayList<Board> win =new ArrayList<Board>();
ArrayList<Board> loose =new ArrayList<Board>();
ArrayList<Board> draw =new ArrayList<Board>();
public Computer()
{
}
public int[] computeMove(Board b)
{
while(true)
{
Random randX = new Random();
Random randY = new Random();
pos[0] = randX.nextInt(3);
pos[1] = randY.nextInt(3);
if(!b.isPosOccupied(pos[0], pos[1]))
{
return pos;
}
}
}
public State getMoves(Board b,int p)
{
//System.out.println("test2");
int x = 0;
int y = 0;
BoardState bs = new BoardState(b,0,0);
//System.out.println("test");
State s = computeMoveAI(bs,p);
//System.out.println("Sore : X : Y" + s.s + s.x + s.y);
return s;
}
private State computeMoveAI(BoardState b, int p) {
// TODO Auto-generated method stub
//System.out.println("Hello");
int[][]sArray = new int[3][3];
for(int i1 =0;i1<3;i1++)
{
for(int j1=0;j1<3;j1++)
{
sArray[i1][j1] = b.br.getVal(i1, j1);
}
}
Board d = new Board(sArray);
//System.out.println("d is ");
//d.display();
//System.out.println("p is "+ p);
int xvalue= b.x;
int yvalue = b.y;
BoardState bs = new BoardState(d,xvalue,yvalue);
if(getConfigScore(d,p) == 1)
{
//System.out.println("Winning Config");
//System.out.println("X is " + b.x + " Y is " + b.y);
// b.br.display();
State s = new State(-1,bs.x,bs.y);
return s;
}
else if (getConfigScore(d,p) == -1)
{
//System.out.println("LooseConfig");
State s = new State(1,bs.x,bs.y);
//System.out.println("Coordinates are "+bs.x + bs.y+ " for " + p);
return s;
}
else if(bs.br.isBoardFull())
{
//System.out.println("Board is full");
State s = new State(0,bs.x,bs.y);
//System.out.println("score " + s.s + "x "+ s.x + "y "+ s.y);
return s;
}
else
{
//Get Turn
//System.out.println("In else condiyion");
int turn;
if(p == 2)
{
turn = 1;
}else
{
turn = 2;
}
ArrayList<BoardState> brr = new ArrayList<BoardState>();
ArrayList<State> st = new ArrayList<State>();
brr = getAllStates(d,p);
for(int k=0;k<brr.size();k++)
{
//System.out.println("Goes in " + "turn " + turn);
//brr.get(k).br.display();
int xxxxx = computeMoveAI(brr.get(k),turn).s;
State temp = new State(xxxxx,brr.get(k).x,brr.get(k).y);
st.add(temp);
}
//Find all Nodes.
//Go to First Node and proceed with recursion.
//System.out.println("Displaying boards");
for(int i=0;i<brr.size();i++)
{
//brr.get(i).br.display();
//System.out.println(brr.get(i).x + " " + brr.get(i).y);
}
//System.out.println("Board configs are");
for(int i=0;i<st.size();i++)
{
//System.out.println(st.get(i).x + " " + st.get(i).y + " and score " + st.get(i).s);
}
//System.out.println("xvalue" + xvalue);
//System.out.println("yvalue" + yvalue);
//System.out.println("Board was");
//d.display();
//System.out.println("Coming to scores");
//System.out.println(" p is "+ p);
if(p == 2)
{
//System.out.println("Size of first response" + st.size());
//System.out.println("Returns Max");
return max(st);
}
else
{
//System.out.println("The last");
return min(st);
}
}
}
private State min(ArrayList<State> st) {
// TODO Auto-generated method stub
ArrayList<State> st1= new ArrayList<State>();
st1= st;
int min = st.get(0).s;
//System.out.println("Min score is " + min);
for(int i=1;i<st1.size();i++)
{
if(min > st1.get(i).s)
{
min = st1.get(i).s;
//System.out.println("Min is");
//System.out.println(min);
//System.out.println("Min" + min);
State s = new State(min,st1.get(i).x,st1.get(i).y);
return s;
}
}
State s = new State(st1.get(0).s,st1.get(0).x,st1.get(0).y);
//System.out.println("Max" + st1.get(0).s);
//System.out.println("Exits Min");
//System.out.println("Min Score" + st1.get(0).s + " x" + st1.get(0).x + "y " + st1.get(0).y);
return s;
}
private State max(ArrayList<State> st) {
// TODO Auto-generated method stub
//System.out.println("Size of first response in funciton is " + st.size());
ArrayList<State> st1= new ArrayList<State>();
st1 = st;
int max = st1.get(0).s;
for(int i=0;i<st1.size();i++)
{
// System.out.println(i+1 + " config is: " + "X:" + st1.get(i).x + "Y:" + st1.get(i).y + " with score " + st1.get(i).s);
}
for(int i=1;i<st1.size();i++)
{
//.out.println("Next Item " + i + st.get(i).s + "Coordinates X"+ st.get(i).x +"Coordinates Y"+ st.get(i).y );
if(max < st1.get(i).s)
{
max = st1.get(i).s;
//System.out.println("Max" + max);
//System.out.println("Max is");
//System.out.println(max);
State s = new State(max,st1.get(i).x,st1.get(i).y);
//System.out.println("Max Score returned" + s.s);
//System.out.println("Returned");
return s;
}
}
State s = new State(st1.get(0).s,st1.get(0).x,st1.get(0).y);
//System.out.println("Max" + st1.get(0).s);
//System.out.println("Max is outer");
//System.out.println(st.get(0).s);
return s;
}
//Basic brain Behind Min Max algorithm
public int getConfigScore(Board b,int p)
{
int score;
int turn ;
int opponent;
if(p == player1)
{
turn = p;
opponent = player2;
}
else
{
turn = player2;
opponent = player1;
}
int[][]sArray = new int[3][3];
for(int i1 =0;i1<3;i1++)
{
for(int j1=0;j1<3;j1++)
{
sArray[i1][j1] = b.getVal(i1, j1);
}
}
Board d = new Board(sArray);
//System.out.println("s arrasy is ");
//d.display();
//System.out.println("turn is " + turn);
if(d.isVictoriousConfig(turn))
{
score = 1;
}
else if(d.isVictoriousConfig(opponent))
{
score = -1;
}
else
{
score = 0;
}
return score;
}
public static ArrayList<BoardState> getAllStates(Board b, int player)
{
ArrayList<BoardState> arr = new ArrayList<BoardState>();
int[][]s1 = new int[3][3];
for(int i1 =0;i1<3;i1++)
{
for(int j1=0;j1<3;j1++)
{
s1[i1][j1] = b.getVal(i1, j1);
}
}
Board d = new Board(s1);
for(int i = 0;i <3; i ++)
{
for (int j=0;j<3;j++)
{
if(!d.isPosOccupied(i, j))
{
int previousState = d.getVal(i, j);
int[][]s = new int[3][3];
for(int i1 =0;i1<3;i1++)
{
for(int j1=0;j1<3;j1++)
{
s[i1][j1] = d.getVal(i1, j1);
}
}
s[i][j] = player;
Board d1 = new Board(s);
BoardState bs = new BoardState(d1,i,j);
arr.add(bs);
}
}
}
return arr;
}
}
This is the output of the test case in the Game class:
Board
1 1 2
2 2 0
1 1 0
Score : X : Y -> 1: 1: 2
The solution here is score:1 for x:1, y:2. It looks correct.
But again, you could say since it is moving sequentially, and since position (1,2) will come before (2,2), it gets the right coordinate.
I understand that this may be huge lines of code to figure out the problem. But
computemoveAI(), getConfigScore() could be the functions to look out for. Also I do not want to bias your thoughts with where I think the problem could as sometimes, we look somewhere , but the problem lies elsewhere.!!

Viterbi algorithm in java

I'm doing the coursera NLP course and the first programming assignment is to build a Viterbi decoder. I think I'm really close to finishing it but there is some elusive bug which I cannot seem to be able to trace. Here is my code:
http://pastie.org/private/ksmbns3gjctedu1zxrehw
http://pastie.org/private/ssv6tc8dwnamn2qegdvww
So far I've debugged the "teaching" related functions so I can say that the parameters for the algorithms are being correctly estimated. Of particular interest is the viterbi() and findW() methods. The definition of the algorithm I'm using can be found here: http://www.cs.columbia.edu/~mcollins/hmms-spring2013.pdf on page 18.
One thing which I'm having hard time wrapping my head around is how am I supposed to update the backpointers for the special cases when K = {1, 2} (in my case this is 0 and 1, since I'm zero-indexing my array) respectively the parameters I'm using in those cases are q({TAGSET} | *, *) and q ({TAGSET} | *, {TAGSET}).
Hints rather than spoon-fed answers will also be highly appreciated!

Here's a simple implementation of viterbi decoder by Yusuke Shunyama =) http://cs.nyu.edu/yusuke/course/NLP/viterbi/Viterbi.java
/*
* Viterbi.java
* Toy Viterbi Decorder
*
* by Yusuke Shinyama <yusuke at cs . nyu . edu>
*
* Permission to use, copy, modify, distribute this software
* for any purpose is hereby granted without fee, provided
* that the above copyright notice appear in all copies and
* that both that copyright notice and this permission notice
* appear in supporting documentation.
*/
import java.awt.*;
import java.util.*;
import java.text.*;
import java.awt.event.*;
import java.applet.*;
class Symbol {
public String name;
public Symbol(String s) {
name = s;
}
}
class SymbolTable {
Hashtable table;
public SymbolTable() {
table = new Hashtable();
}
public Symbol intern(String s) {
s = s.toLowerCase();
Object sym = table.get(s);
if (sym == null) {
sym = new Symbol(s);
table.put(s, sym);
}
return (Symbol)sym;
}
}
class SymbolList {
Vector list;
public SymbolList() {
list = new Vector();
}
public int size() {
return list.size();
}
public void set(int index, Symbol sym) {
list.setElementAt(sym, index);
}
public void add(Symbol sym) {
list.addElement(sym);
}
public Symbol get(int index) {
return (Symbol) list.elementAt(index);
}
}
class IntegerList {
Vector list;
public IntegerList() {
list = new Vector();
}
public int size() {
return list.size();
}
public void set(int index, int i) {
list.setElementAt(new Integer(i), index);
}
public void add(int i) {
list.addElement(new Integer(i));
}
public int get(int index) {
return ((Integer)list.elementAt(index)).intValue();
}
}
class ProbTable {
Hashtable table;
public ProbTable() {
table = new Hashtable();
}
public void put(Object obj, double prob) {
table.put(obj, new Double(prob));
}
public double get(Object obj) {
Double prob = (Double)table.get(obj);
if (prob == null) {
return 0.0;
}
return prob.doubleValue();
}
// normalize probability
public void normalize() {
double total = 0.0;
for(Enumeration e = table.elements() ; e.hasMoreElements() ;) {
total += ((Double)e.nextElement()).doubleValue();
}
if (total == 0.0) {
return; // div by zero!
}
for(Enumeration e = table.keys() ; e.hasMoreElements() ;) {
Object k = e.nextElement();
double prob = ((Double)table.get(k)).doubleValue();
table.put(k, new Double(prob / total));
}
}
}
class State {
public String name;
ProbTable emits;
ProbTable linksto;
public State(String s) {
name = s;
emits = new ProbTable();
linksto = new ProbTable();
}
public void normalize() {
emits.normalize();
linksto.normalize();
}
public void addSymbol(Symbol sym, double prob) {
emits.put(sym, prob);
}
public double emitprob(Symbol sym) {
return emits.get(sym);
}
public void addLink(State st, double prob) {
linksto.put(st, prob);
}
public double transprob(State st) {
return linksto.get(st);
}
}
class StateTable {
Hashtable table;
public StateTable() {
table = new Hashtable();
}
public State get(String s) {
s = s.toUpperCase();
State st = (State)table.get(s);
if (st == null) {
st = new State(s);
table.put(s, st);
}
return st;
}
}
class StateIDTable {
Hashtable table;
public StateIDTable() {
table = new Hashtable();
}
public void put(State obj, int i) {
table.put(obj, new Integer(i));
}
public int get(State obj) {
Integer i = (Integer)table.get(obj);
if (i == null) {
return 0;
}
return i.intValue();
}
}
class StateList {
Vector list;
public StateList() {
list = new Vector();
}
public int size() {
return list.size();
}
public void set(int index, State st) {
list.setElementAt(st, index);
}
public void add(State st) {
list.addElement(st);
}
public State get(int index) {
return (State) list.elementAt(index);
}
}
class HMMCanvas extends Canvas {
static final int grid_x = 60;
static final int grid_y = 40;
static final int offset_x = 70;
static final int offset_y = 30;
static final int offset_y2 = 10;
static final int offset_y3 = 65;
static final int col_x = 40;
static final int col_y = 10;
static final int state_r = 10;
static final Color state_fill = Color.white;
static final Color state_fill_maximum = Color.yellow;
static final Color state_fill_best = Color.red;
static final Color state_boundery = Color.black;
static final Color link_normal = Color.green;
static final Color link_processed = Color.blue;
static final Color link_maximum = Color.red;
HMMDecoder hmm;
public HMMCanvas() {
setBackground(Color.white);
setSize(400,300);
}
public void setHMM(HMMDecoder h) {
hmm = h;
}
private void drawState(Graphics g, int x, int y, Color c) {
x = x * grid_x + offset_x;
y = y * grid_y + offset_y;
g.setColor(c);
g.fillOval(x-state_r, y-state_r, state_r*2, state_r*2);
g.setColor(state_boundery);
g.drawOval(x-state_r, y-state_r, state_r*2, state_r*2);
}
private void drawLink(Graphics g, int x, int y0, int y1, Color c) {
int x0 = grid_x * x + offset_x;
int x1 = grid_x * (x+1) + offset_x;
y0 = y0 * grid_y + offset_y;
y1 = y1 * grid_y + offset_y;
g.setColor(c);
g.drawLine(x0, y0, x1, y1);
}
private void drawCenterString(Graphics g, String s, int x, int y) {
x = x - g.getFontMetrics().stringWidth(s)/2;
g.setColor(Color.black);
g.drawString(s, x, y+5);
}
private void drawRightString(Graphics g, String s, int x, int y) {
x = x - g.getFontMetrics().stringWidth(s);
g.setColor(Color.black);
g.drawString(s, x, y+5);
}
public void paint(Graphics g) {
if (hmm == null) {
return;
}
DecimalFormat form = new DecimalFormat("0.0000");
int nsymbols = hmm.symbols.size();
int nstates = hmm.states.size();
// complete graph.
for(int i = 0; i < nsymbols; i++) {
int offset_ymax = offset_y2+nstates*grid_y;
if (i < nsymbols-1) {
for(int y1 = 0; y1 < nstates; y1++) {
for(int y0 = 0; y0 < nstates; y0++) {
Color c = link_normal;
if (hmm.stage == i+1 && hmm.i0 == y0 && hmm.i1 == y1) {
c = link_processed;
}
if (hmm.matrix_prevstate[i+1][y1] == y0) {
c = link_maximum;
}
drawLink(g, i, y0, y1, c);
if (c == link_maximum && 0 < i) {
double transprob = hmm.states.get(y0).transprob(hmm.states.get(y1));
drawCenterString(g, form.format(transprob),
offset_x + i*grid_x + grid_x/2, offset_ymax);
offset_ymax = offset_ymax + 16;
}
}
}
}
// state circles.
for(int y = 0; y < nstates; y++) {
Color c = state_fill;
if (hmm.matrix_prevstate[i][y] != -1) {
c = state_fill_maximum;
}
if (hmm.sequence.size() == nsymbols &&
hmm.sequence.get(nsymbols-1-i) == y) {
c = state_fill_best;
}
drawState(g, i, y, c);
}
}
// max probability.
for(int i = 0; i < nsymbols; i++) {
for(int y1 = 0; y1 < nstates; y1++) {
if (hmm.matrix_prevstate[i][y1] != -1) {
drawCenterString(g, form.format(hmm.matrix_maxprob[i][y1]),
offset_x+i*grid_x, offset_y+y1*grid_y);
}
}
}
// captions (symbols atop)
for(int i = 0; i < nsymbols; i++) {
drawCenterString(g, hmm.symbols.get(i).name, offset_x+i*grid_x, col_y);
}
// captions (states in left)
for(int y = 0; y < nstates; y++) {
drawRightString(g, hmm.states.get(y).name, col_x, offset_y+y*grid_y);
}
// status bar
g.setColor(Color.black);
g.drawString(hmm.status, col_x, offset_y3+nstates*grid_y);
g.drawString(hmm.status2, col_x, offset_y3+nstates*grid_y+16);
}
}
class HMMDecoder {
StateList states;
int state_start;
int state_end;
public IntegerList sequence;
public double[][] matrix_maxprob;
public int[][] matrix_prevstate;
public SymbolList symbols;
public double probmax;
public int stage, i0, i1;
public boolean laststage;
public String status, status2;
public HMMDecoder() {
status = "Not initialized.";
status2 = "";
states = new StateList();
}
public void addStartState(State st) {
state_start = states.size(); // get current index
states.add(st);
}
public void addNormalState(State st) {
states.add(st);
}
public void addEndState(State st) {
state_end = states.size(); // get current index
states.add(st);
}
// for debugging.
public void showmatrix() {
for(int i = 0; i < symbols.size(); i++) {
for(int j = 0; j < states.size(); j++) {
System.out.print(matrix_maxprob[i][j]+" "+matrix_prevstate[i][j]+", ");
}
System.out.println();
}
}
// initialize for decoding
public void initialize(SymbolList syms) {
// symbols[syms.length] should be END
symbols = syms;
matrix_maxprob = new double[symbols.size()][states.size()];
matrix_prevstate = new int[symbols.size()][states.size()];
for(int i = 0; i < symbols.size(); i++) {
for(int j = 0; j < states.size(); j++) {
matrix_prevstate[i][j] = -1;
}
}
State start = states.get(state_start);
for(int i = 0; i < states.size(); i++) {
matrix_maxprob[0][i] = start.transprob(states.get(i));
matrix_prevstate[0][i] = 0;
}
stage = 0;
i0 = -1;
i1 = -1;
sequence = new IntegerList();
status = "Ok, let's get started...";
status2 = "";
}
// forward procedure
public boolean proceed_decoding() {
status2 = "";
// already end?
if (symbols.size() <= stage) {
return false;
}
// not started?
if (stage == 0) {
stage = 1;
i0 = 0;
i1 = 0;
matrix_maxprob[stage][i1] = 0.0;
} else {
i0++;
if (states.size() <= i0) {
// i0 should be reinitialized.
i0 = 0;
i1++;
if (states.size() <= i1) {
// i1 should be reinitialized.
// goto next stage.
stage++;
if (symbols.size() <= stage) {
// done.
status = "Decoding finished.";
return false;
}
laststage = (stage == symbols.size()-1);
i1 = 0;
}
matrix_maxprob[stage][i1] = 0.0;
}
}
// sym1: next symbol
Symbol sym1 = symbols.get(stage);
State s0 = states.get(i0);
State s1 = states.get(i1);
// precond: 1 <= stage.
double prob = matrix_maxprob[stage-1][i0];
DecimalFormat form = new DecimalFormat("0.0000");
status = "Prob:" + form.format(prob);
if (1 < stage) {
// skip first stage.
double transprob = s0.transprob(s1);
prob = prob * transprob;
status = status + " x " + form.format(transprob);
}
double emitprob = s1.emitprob(sym1);
prob = prob * emitprob;
status = status + " x " + form.format(emitprob) + "(" + s1.name+":"+sym1.name + ")";
status = status + " = " + form.format(prob);
// System.out.println("stage: "+stage+", i0:"+i0+", i1:"+i1+", prob:"+prob);
if (matrix_maxprob[stage][i1] < prob) {
matrix_maxprob[stage][i1] = prob;
matrix_prevstate[stage][i1] = i0;
status2 = "(new maximum found)";
}
return true;
}
// backward proc
public void backward() {
int probmaxstate = state_end;
sequence.add(probmaxstate);
for(int i = symbols.size()-1; 0 < i; i--) {
probmaxstate = matrix_prevstate[i][probmaxstate];
if (probmaxstate == -1) {
status2 = "Decoding failed.";
return;
}
sequence.add(probmaxstate);
//System.out.println("stage: "+i+", state:"+probmaxstate);
}
}
}
public class Viterbi extends Applet implements ActionListener, Runnable {
SymbolTable symtab;
StateTable sttab;
HMMDecoder myhmm = null;
HMMCanvas canvas;
Panel p;
TextArea hmmdesc;
TextField sentence;
Button bstart, bskip;
static final String initialHMM =
"start: go(cow,1.0)\n" +
"cow: emit(moo,0.9) emit(hello,0.1) go(cow,0.5) go(duck,0.3) go(end,0.2)\n" +
"duck: emit(quack,0.6) emit(hello,0.4) go(duck,0.5) go(cow,0.3) go(end,0.2)\n";
final int sleepmillisec = 100; // 0.1s
// setup hmm
// success:true.
boolean setupHMM(String s) {
myhmm = new HMMDecoder();
symtab = new SymbolTable();
sttab = new StateTable();
State start = sttab.get("start");
State end = sttab.get("end");
myhmm.addStartState(start);
boolean success = true;
StringTokenizer lines = new StringTokenizer(s, "\n");
while (lines.hasMoreTokens()) {
// foreach line.
String line = lines.nextToken();
int i = line.indexOf(':');
if (i == -1) break;
State st0 = sttab.get(line.substring(0,i).trim());
if (st0 != start && st0 != end) {
myhmm.addNormalState(st0);
}
//System.out.println(st0.name+":"+line.substring(i+1));
StringTokenizer tokenz = new StringTokenizer(line.substring(i+1), ", ");
while (tokenz.hasMoreTokens()) {
// foreach token.
String t = tokenz.nextToken().toLowerCase();
if (t.startsWith("go(")) {
State st1 = sttab.get(t.substring(3).trim());
// fetch another token.
if (!tokenz.hasMoreTokens()) {
success = false; // err. nomoretoken
break;
}
String n = tokenz.nextToken().replace(')', ' ');
double prob;
try {
prob = Double.valueOf(n).doubleValue();
} catch (NumberFormatException e) {
success = false; // err.
prob = 0.0;
}
st0.addLink(st1, prob);
//System.out.println("go:"+st1.name+","+prob);
} else if (t.startsWith("emit(")) {
Symbol sym = symtab.intern(t.substring(5).trim());
// fetch another token.
if (!tokenz.hasMoreTokens()) {
success = false; // err. nomoretoken
break;
}
String n = tokenz.nextToken().replace(')', ' ');
double prob;
try {
prob = Double.valueOf(n).doubleValue();
} catch (NumberFormatException e) {
success = false; // err.
prob = 0.0;
}
st0.addSymbol(sym, prob);
//System.out.println("emit:"+sym.name+","+prob);
} else {
// illegal syntax, just ignore
break;
}
}
st0.normalize(); // normalize probability
}
end.addSymbol(symtab.intern("end"), 1.0);
myhmm.addEndState(end);
return success;
}
// success:true.
boolean setup() {
if (! setupHMM(hmmdesc.getText()))
return false;
// initialize words
SymbolList words = new SymbolList();
StringTokenizer tokenz = new StringTokenizer(sentence.getText());
words.add(symtab.intern("start"));
while (tokenz.hasMoreTokens()) {
words.add(symtab.intern(tokenz.nextToken()));
}
words.add(symtab.intern("end"));
myhmm.initialize(words);
canvas.setHMM(myhmm);
return true;
}
public void init() {
canvas = new HMMCanvas();
setLayout(new BorderLayout());
p = new Panel();
sentence = new TextField("moo hello quack", 20);
bstart = new Button(" Start ");
bskip = new Button("Auto");
bstart.addActionListener(this);
bskip.addActionListener(this);
p.add(sentence);
p.add(bstart);
p.add(bskip);
hmmdesc = new TextArea(initialHMM, 4, 20);
add("North", canvas);
add("Center", p);
add("South", hmmdesc);
}
void setup_fallback() {
// adjustable
State cow = sttab.get("cow");
State duck = sttab.get("duck");
State end = sttab.get("end");
cow.addLink (cow, 0.5);
cow.addLink (duck, 0.3);
cow.addLink (end, 0.2);
duck.addLink (cow, 0.3);
duck.addLink (duck, 0.5);
duck.addLink (end, 0.2);
cow.addSymbol(symtab.intern("moo"), 0.9);
cow.addSymbol(symtab.intern("hello"), 0.1);
duck.addSymbol(symtab.intern("quack"), 0.6);
duck.addSymbol(symtab.intern("hello"), 0.4);
}
public void destroy() {
remove(p);
remove(canvas);
}
public void processEvent(AWTEvent e) {
if (e.getID() == Event.WINDOW_DESTROY) {
System.exit(0);
}
}
public void run() {
if (myhmm != null) {
while (myhmm.proceed_decoding()) {
canvas.repaint();
try {
Thread.sleep(sleepmillisec);
} catch (InterruptedException e) {
;
}
}
myhmm.backward();
canvas.repaint();
bstart.setLabel(" Start ");
bstart.setEnabled(true);
bskip.setEnabled(true);
myhmm = null;
}
}
public void actionPerformed(ActionEvent ev) {
String label = ev.getActionCommand();
if (label.equalsIgnoreCase(" start ")) {
if (!setup()) {
// error
return;
}
bstart.setLabel("Proceed");
canvas.repaint();
} else if (label.equalsIgnoreCase("proceed")) {
// next
if (! myhmm.proceed_decoding()) {
myhmm.backward();
bstart.setLabel(" Start ");
myhmm = null;
}
canvas.repaint();
} else if (label.equalsIgnoreCase("auto")) {
// skip
if (myhmm == null) {
if (!setup()) {
// error
return;
}
}
bstart.setEnabled(false);
bskip.setEnabled(false);
Thread me = new Thread(this);
me.setPriority(Thread.MIN_PRIORITY);
// start animation.
me.start();
}
}
public static void main(String args[]) {
Frame f = new Frame("Viterbi");
Viterbi v = new Viterbi();
f.add("Center", v);
f.setSize(400, 400);
f.show();
v.init();
v.start();
}
public String getAppletInfo() {
return "A Sample Viterbi Decoder Applet";
}
}

Here are some suggestions:
You should draw out the HMM lattice if you have any confusion about how transitions are occurring in your model.
For instance, you can view transitions to the first hidden state as originating from a single start hidden state, so the backpointer for k=0 would always have to point to this start state. In your code, you probably should not be looping over hidden states for k=0 in findW (which seems correct), but you probably should be looping for k=1.
Usually multiplying transition and emission probabilities in HMM inference lead to very small floating point values, which can lead to numerical errors. You should add log probabilities instead of multiplying probabilities.
To check viterbi or forward-backward implementations, I usually also write a brute force method and compare the output of each. If the brute-force and dynamic-programming algorithm match on short sequences, then that gives a reasonable measure of confidence that both are correct.

A* implementation issue

I am using A* for pathfinding in a Java project that I am working on. My attempt at implementing it though, has some issues. Not only is it slightly slow, but it sometimes runs into infinite loop issues where it never finds a path. I believe this to be the result of a bug somewhere in my code. The pathfinder operates on 3d space, and uses a basic heuristic (I can provide the code if necessary, however, it does little more than just calculate the distance squared between the two points).
The code is here:
public class BinaryPathFinder extends PathFinder {
private final PriorityBuffer<PathNode> paths;
private final HashMap<Point, Integer> mindists = new HashMap<Point, Integer>();
private final ComparableComparator<PathNode> comparator = new ComparableComparator<PathNode>();
private Path lastPath;
private Point start, end;
private final byte SIZE_INCREMENT = 20;
public BinaryPathFinder(PathHeuristic heuristic,
Pathplayer player, PathWorld pathWorld) {
super(heuristic, player, pathWorld);
this.world = pathWorld.getWorld();
paths = new PriorityBuffer<PathNode>(8000, comparator);
}
#Override
public boolean find() {
try {
PathNode root = new PathNode();
root.point = start;
calculateTotalCost(root, start, start, false);
expand(root);
while (true) {
PathNode p = paths.remove();
if (p == null)
return false;
Point last = p.point;
if (isGoal(last)) {
calculatePath(p); // Iterate back.
this.mindists.clear();
this.paths.clear();
return true;
}
expand(p);
}
} catch (Exception e) {
e.printStackTrace();
}
this.mindists.clear();
this.paths.clear();
return false;
}
#Override
public Path path() {
return this.lastPath;
}
#Override
public void recalculate(Point start, Point end) {
this.start = start;
this.end = end;
this.lastPath = null;
}
private void expand(PathNode path) {
Point p = path.point;
Integer min = mindists.get(p);
if (min == null || min > path.totalCost)
mindists.put(p, path.totalCost);
else
return;
Point[] successors = generateSuccessors(p);
for (Point t : successors) {
if (t == null)
continue;
PathNode newPath = new PathNode(path);
newPath.point = t;
calculateTotalCost(newPath, p, t, false);
paths.add(newPath);
}
}
private void calculatePath(PathNode p) {
Point[] retPath = new Point[20];
Point[] copy = null;
short added = 0;
for (PathNode i = p; i != null; i = i.parent) {
if (added >= retPath.length) {
copy = new Point[retPath.length + SIZE_INCREMENT];
System.arraycopy(retPath, 0, copy, 0, retPath.length);
retPath = copy;
}
retPath[added++] = i.point;
}
this.lastPath = new Path(retPath);
}
private int calculateHeuristic(Point start, Point end, boolean endPoint) {
return this.heuristic.calculate(start, end, this.pathWorld,
this.player, endPoint);
}
private int calculateTotalCost(PathNode p, Point from, Point to,
boolean endPoint) {
int g = (calculateHeuristic(from, to, endPoint) + ((p.parent != null) ? p.parent.cost
: 0));
int h = calculateHeuristic(from, to, endPoint);
p.cost = g;
p.totalCost = (g + h);
return p.totalCost;
}
private Point[] generateSuccessors(Point point) {
Point[] points = new Point[27];
Point temp = null;
byte counter = -1;
for (int x = point.x - 1; x <= point.x + 1; ++x) {
for (int y = point.y + 1; y >= point.y - 1; --y) {
for (int z = point.z - 1; z <= point.z + 1; ++z) {
++counter;
if (x == 0 && y == 0 && z == 0)
continue;
temp = new Point(x, y, z);
if (valid(temp))
points[counter] = temp;
}
}
}
return points;
}
private boolean isGoal(Point last) {
return last.equals(this.end);
}
}
PathNode is here:
public class PathNode implements Comparable<PathNode> {
public Point point;
public final PathNode parent;
public int cost;
public int totalCost;
public PathNode(Point point, PathNode parent, short cost, short totalCost) {
this.point = point;
this.parent = parent;
this.cost = cost;
this.totalCost = totalCost;
}
public PathNode() {
this.point = null;
this.parent = null;
this.cost = this.totalCost = 0;
}
public PathNode(PathNode path) {
this.parent = path;
this.cost = path.cost;
this.totalCost = path.totalCost;
}
#Override
public int compareTo(PathNode node) {
int result = node.totalCost - node.cost;
if (result > node.totalCost)
return 1;
else if (result == 0)
return 0;
else
return -1;
}
}
Point is just a wrapper class that defines integer x, y, z values.
I am using the Apache Commons PriorityBuffer for storing path nodes.
Help would be appreciated - thanks in advance!

just from a programming point of view - are you sure that
for(PathNode i = p; i != null; i = i.parent) always terminates? this looks like the only place it could really hang.