Adversarial Search

(written 2023)

Two-player, Zero Sum games

  • State-machine
    • to-move: state \(\to\) player
    • actions: state \(\to\) {action}
    • result: state \(\times\) action \(\to\) state
    • utility: state \(\times\) player \(\to\mathbb{R}\)
  • Minimax algorithm:
    • maximises utility for the player currently to move
    • Tree Search: optimise utility bottom-up
      • min nodes and max nodes
    • exhaustive research
  • Caveats and variations
    • Branching factor
    • multi-player games - alliances and trust
    • co-operative games
    • \(\alpha\beta\) pruning
    • heuristic searches
    • Type A and Type B:
      • move generation
      • move evaluation
  • Monte Carlo Tree Search
    • Monte Carlo \(\sim\) Stochastic Simulation
    • Balance Exploitation and Exploration
  • More Caveats
    • Stochastic Games - Chance Nodes
    • Partially Observable Games
      • the percept sequence is no longer the opponent’s move.
    • Limitations - Section 6.7
      • Intractible
    • Approximations and Assumptions
    • Individual moves - no sight of the bigger picture