In Pursuit of the Traveling Salesman

Preface xi Chapter 1: Challenges 1 Tour of the United States 2 An Impossible Task? 6 One Problem at a Time 10 Road Map of the Book 16 Chapter 2: Origins of the Problem 19 Before the Mathematicians 19 Euler and Hamilton 27 Vienna to Harvard to Princeton 35 And on to the RAND Corporation 38 A Statistical View 39 Chapter 3: The Salesman in Action 44 Road Trips 44 Mapping Genomes 49 Aiming Telescopes, X-rays, and Lasers 51 Guiding Industrial Machines 53 Organizing Data 56 Tests for Microprocessors 59 Scheduling Jobs 60 And More 60 Chapter 4: Searching for a Tour 62 The 48-States Problem 62 Growing Trees and Tours 65 AlterationsWhile You Wait 75 Borrowing from Physics and Biology 84 The DIMACS Challenge 91 Tour Champions 92 Chapter 5: Linear Programming 94 General-Purpose Model 94 The Simplex Algorithm 99 Two for the Price of One: LP Duality 105 The Degree LP Relaxation of the TSP 108 Eliminating Subtours 113 A Perfect Relaxation 118 Integer Programming 122 Operations Research 125 Chapter 6: Cutting Planes 127 The Cutting-Plane Method 127 A Catalog of TSP Inequalities 131 The Separation Problem 137 Edmonds's Glimpse of Heaven 142 Cutting Planes for Integer Programming 144 Chapter 7: Branching 146 Breaking Up 146 The Search Party 148 Branch-and-bound for Integer Programming 151 Chapter 8: Big Computing 153 World Records 153 The TSP on a Grand Scale 163 Chapter 9: Complexity 168 A Model of Computation 169 The Campaign of Jack Edmonds 171 Cook's Theorem and Karp's List 174 State of the TSP 178 Do We Need Computers? 184 Chapter 10: The Human Touch 191 Humans versus Computers 191 Tour-finding Strategies 192 The TSP in Neuroscience 196 Animals Solving the TSP 197 Chapter 11: Aesthetics 199 Julian Lethbridge 199 Jordan Curves 201 Continuous Lines 205 Art and Mathematics 207 Chapter 12: Pushing the Limits 211 Notes 213 Bibliography 223 Index 225

William J. Cook is professor of combinatorics and optimization at the University of Waterloo. He is the coauthor of The Traveling Salesman Problem: A Computational Study (Princeton).