Contents

• 0. Preface
• 0.1. Acknowledgments
• 1. An N-Body Code
• 1.1. First Attempt
• 1.2. Driver
• 1.3. Input
• 2. N-Body Integrators
• 2.1. Inspecting the Leapfrog
• 2.2. Acceleration
• 2.3. Newtonian Gravity
• 2.4. A Matter of Taste
• 2.5. Potential Energy
• 2.6. Local Arrays
• 2.7. Energy Diagnostics
• 3. Testing the N-body Code
• 3.1. A 2-Body System
• 3.2. A Bug
• 3.3. The Simplest Case
• 3.4. A Variation
• 3.5. Another Variation
• 3.6. Two Variations
• 3.7. A Single Time Step
• 4. Debugging the N-body Code
• 4.1. Forward Euler
• 4.2. Nothing Wrong
• 4.3. Two Possibilities
• 4.4. Back to Square One
• 4.5. A Warning Light
• 4.6. Hindsight
• 4.7. Bug Fixed
• 4.8. One More Check
• 5. A Single-Links Version
• 5.1. A Figure-8 Triple
• 5.2. Switching Places
• 5.3. Single Links in Body
• 5.4. Single Links in Nbody
• 5.5. The DRY Principle
• 5.6. Simplifying Further
• 5.7. Finishing the Revision
• 5.8. Two Tests
• 6. Returning to Simplicity
• 6.1. Extra Body Variables
• 6.2. Alternatives
• 6.3. Forward
• 6.4. Clean Code
• 6.5. Sending a String
• 6.6. Wishful Thinking
• 6.7. Implementation
• 6.8. Indirect String Sending
• 6.9. The Same, Yet Different
• 6.10. Testing
• 7. A Final Version
• 7.1. Clarity
• 7.2. Brevity
• 7.3. Correctness
• 7.4. More Information
• 7.5. An Initial Snapshot Output
• 7.6. A New Driver
• 7.7. A Final Test
• 8. An Eight-Body System
• 8.1. Setting Up a Cube
• 8.2. Letting Go
• 8.3. Passing Through
• 8.4. Convergence
• 9. Softening
• 9.1. Close Encounters
• 9.2. Fuzzy-Point Particles
• 9.3. A New Driver
• 9.4. A Code with Softening
• 9.5. Details
• 10. Cold Collapse with Softening
• 10.1. Check
• 10.2. Large Softening
• 10.3. Even larger softening
• 10.4. Small Softening
• 10.5. Central Collapse
• 11. Literature References