1. The Move Decision Strategy of Indigo Author: Bruno Bouzy Presented by: Ling Zhao University of Alberta March 7, 2007

2. 2 Outline Models Low level modules: pattern match, string search, move generation, quick evaluation Middle level modules: global quiescence search, group search, strategic group evaluation High level modules: calm method, urgent method, slow life & death method. Experiments

3. 3 Classic Model Examples: Chinook, Deep Blue, Logistello

4. 4 Indigo Model

5. 5 Top Level Calm method, urgent method, and L&D method each chooses one move with the best incentive. Top level decides the best move by assessing the different incentives.

6. 6 String Capture Tree Search Target: strings with 1 or 2 liberties. Method: alpha-beta search with transposition table.

7. 7 Quick Evaluation An approximation of the set of groups and territories. Use const time, very fast, provide rough estimate. Main method: mathematical morphology.

8. 8 Dilation & Erosion 0 0 0 0 0 0 0 0 64 0 0 64 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 1 64 1 1 64 1 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 D1D1 0 0 0 1 0 0 1 0 0 0 0 0 2 2 2 2 2 0 0 0 0 1 2 64 3 3 64 2 1 0 0 0 2 2 2 2 2 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 D2D2 0 0 0 1 0 0 1 0 0 0 0 0 2 2 2 2 2 2 0 0 0 2 4 6 5 5 6 4 2 0 1 2 6 64 7 7 64 6 2 1 0 2 4 6 5 5 6 4 2 0 0 0 2 2 2 2 2 2 0 0 0 0 0 1 0 0 1 0 0 0 D3D3 0 0 0 0 0 0 0 0 2 1 1 2 0 0 0 0 0 4 6 5 5 6 4 0 0 0 2 6 64 7 7 64 6 2 0 0 0 4 6 5 5 6 4 0 0 0 0 0 2 1 1 2 0 0 0 0 0 0 0 0 E 1 o D 3 0 0 0 0 0 0 0 0 64 7 7 64 0 0 0 0 0 0 0 0 E 7 o D 3 e = d (d-1) +1

9. 9 Move Generation Select plausible moves instead of all legal moves. Use domain-dependent information: string capture tree search, local shapes, dividers, connectors, eyes, simple life & death shapes, territory growing/reducing. Knowledge represented by 300 patterns. Two important properties: urgency, ordering/disordering property.

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11. 11 Strategic Method Goal: estimate the strategic importance of killing or saving groups, in order to focus resources on important ones. Single-agent search to determine the number of consecutive moves by one side to kill/save a group. Result = [K|L]. Life & death search performs only on groups with K,L <= 2.

12. 12 L&D Group Search Position evaluation changes dramatically when death occurs: If a group is considered dead by quick EF, opponents groups that kills it should aggregate around it. Data structure needs to be updated after it. Then another pass of quick EF. Quick EF must be prudent to determine death (life is OK).

13. 13 State of Groups Two two-player look-aheads performed along L&D of groups, for each side playing first. Evaluated by quick EF. Reliable states: {W|W}, {L|L}, {W|L}, {L|W}. Unreliable states: {W|?}, {?|L}, {?|?}, {?|W}, {L|?}.

14. 14 Difficulties in Group L&D Groups can grow: search explosion. Groups can split: each new group has its own L&D results. Remedy: ignore them. Only consider if the whole group lives or dies.

15. 15 Urgent Method Most relevant and important method in Indigo. Urgency heuristics play well but not optimally. Weakness of static heuristics lies in the lack of verification of the move effect. Indigo uses selective quiescence search to verify that the best urgent move do not decrease position evaluation using quick EF. Not all urgent moves can be verified using tree search.

16. 16 Find Best Urgent Move In middle game, it is assumed that strategies are mainly based on dividing/splitting/connecting notion. 8-connection is used to divide opponent. 4-connection is used to connect friendly stones.

17. 17 Goal Focus Stability Consistency of play: if a move is played to divide opponent, then another move is highly possible to continue the goal. Doubling urgency: G has twice urgency as E. No need to double urgency for string capture goal, since string size is increased, and so is the urgency.

18. 18 Move Urgency

19. 19 Calm Method Global selective quiescence search + quick EF at leaf nodes. Only a certain urgent moves are tried. Search forbids disordering moves after a certain depth. Disordering moves are those that decrease the stability of groups. Max depth = 15, Average branching factor = 2~3

20. 20 Experiments Urgent vs. calm method: Const vs. doubling strategy: Quiescence search vs. quick EF:

21. 21 Summary An overview of a Go program with 10+ year research. Urgency and ordering/disordering used in Indigo are interesting. How to combine urgency and positional evaluation?