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Introduction

A* is a widely used algorithm in pathfinding and graph traversal. Due to its pheonemnal performance and accruacy, it is utilized extensively in applications such as maps, vehicle routing, and robotics.

The core of A* lies at the heuristic used to determine the order of node expansion. Heuristics are essentially estimates of the cost of getting to the goal from a particular node. Heuristics take in consideration both the forward cost, and the backward cost.

For more info, see Wikipedia

Summary

This work was part of an undergradute AI class I took at UCDavis. This project implements several A* Modules with different heuristics to determine the best path to reach the peak of Mount Saint Helena.

Theoretical worlds are imposed in which the implementations are put to the test. Each of which can be defined by their cost function. More concretely, the worlds can be described by:

 // Exponential of the height difference
 public double getCost(final Point p1, final Point p2) {
     return Math.pow(2.0, (getTile(p2) - getTile(p1)));
 }
 // Bizzaro world cost function
 public double getCost(final Point p1, final Point p2) {
     return 1.0*(getTile(p1) / (getTile(p2) + 1));
 }

Prerequisite

Before you compile and run the modules, make sure you are in the src/main/java directory.

Compiling & Running

To compile, run the following command in your terminal:

javac *.java

To run any of the AI modules on a randomly generated map, use the following command:

java Main <AIModule>

To run any of the AI modules on the Mount Helena map, use the following command:

java -Xmx1024M Main -load ../resources/MTAFT.XYZ <AIModule>

To run mutiple AI Modules, use the following command:

java Main <AIModule> <AIModule> ...

To run with a specific seed to the random map generator, use the following command:

java Main <AIModule> -seed <number>

Implementing your own AI Module

To implement your own AI Module, you need to write a class that implements the AIModule interface. For examples, see the StupidAI.java or AStarExp.java.

Once you've implemented your own module, you can use the same commands in the Compiling & Running section to test the performance of your AI.

Explanation

I implemented two AI Modules, namely AStarDiv and AStarExp. Feel free to check those out. The Explanation.pdf contains a detailed explanation and proof of admissability of the heuristics used in those modules.