transposition table ?

[brunoscherrer]

Suppose I want to implement a basic algorithm such as AlphaBeta with transposition table for a deterministic game with full observability, I would need a function key(state) such that if any two states s1 and s2 are equivalent (in the sense they have similar futures, whatever the past) then key(s1)=key(s2).
I haven't found such a function in the API.

At first glance, I have the feeling that serialize() may produce different results for equivalent states. Similarly, I have the feeling that state representation may produce identical results for different states (eg in chess there are special rules about repetitions, en passant, etc...)

Have I missed something ? (sorry if this is the case)

[lanctot]

Hi @brunoscherrer,

Correct this does not exist in the general, but it is implemented separately in some games (see e.g. the Zobrist hashing in chess_common.h and chess_board.h) which should be easy to adapt to a different game.

For the the games of interest (2p perfect info games), a hash built from the State::ToString() (str(state)) would be uniquely identifying the state, though. That would work for a general game-independent transposition table.