Author: Tim Foden
Date: 08:46:07 04/04/02
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On April 03, 2002 at 17:31:42, Heiner Marxen wrote: >On April 03, 2002 at 16:11:36, Tim Foden wrote: > >>Hi Heiner, >> >>I just thought of something to ask you. In Chest you have hash tables... how do >>you cope with the Graph History Interaction problem? In most normal chess >>programs this is simply ignored, but I would have thought that you couldn't >>ignore it in Chest, in case you gave invalid results. >> >>Cheers, Tim. > >I'm not sure I understand completely. >Do you mean that the board contents is not enough, and we need to consider >the history, how we come there? Yes. >Then, no, I do not explicitly do much about it, i.e. I ignore that problem, >since (for Chest) it is no problem. > >First, I ignore the 50-move rule. >Then, Chest always does internal iterative deepening. Therefore, each subtree >of a solution tree always is of shortest possible depth. >And if you think further... no position can appear twice on any path that >is part of such a solution tree. > >Chest detects repeated position in its path indirectly via the hash table (TT), >since it does create (and lock) a hash table entry when starting a recursive >search, and gradually updates the known value of the entry, until the search >is finished, the last result is entered, and the entry is unlocked. > >Any nested search of the same position will find a result with a larger depth >in it, as the recursive search needs. That will cut off there. >Note that I do NOT return any "impossible" value upon detection of a cycle. >_That_ would create anomalies and false results. > >I strictly stick to the dogma, that the function that is cached in the TT >must depend _only_ on the key of the TT-entry, i.e. the board (inclusive >ep status and castling rights and side to move). > >I hope to have answered your question. I think you probably have, thanks... but I'll have to think about it for a while! :) Cheers, Tim.
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