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Subject: Re: Can we use hash table at root?

Author: Vincent Diepeveen

Date: 05:33:10 02/01/00

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On February 01, 2000 at 05:55:39, Tijs van Dam wrote:

i have a special function doing the first ply for me.
i have a special variable there to store the move diep is gonna play.
the rest i get out of the hashtables.

note that i use 8 probe and depth replacement, so it's very unlikely that
the root move is not equal to the move in the hashtable.

>On January 31, 2000 at 19:42:37, Vincent Diepeveen wrote:
>>On January 31, 2000 at 16:48:41, Tim wrote:
>>>Crafty does not use(store and probe) hash table at root.
>>>How about other programs?
>>>Is there problem to use hash table at root?
>>It depends upon how you write to hashtable,
>>but in general spoken it is not possible.
>>Suppose you get to the same position as the root position somewhre in
>>your lines, which is very likely. now suppose one day that's with
>>difference alfa and beta values, so even though you already have it
>>in the hashtable you might overwrite it with a small depth, say 1 ply.
>>then you need to abort your search. searching PV of this ply is not ready
>>yet. In your hashtable is only a 1 ply search from this position.
>>Bad luck. all those plies searched for nothing...
>I don't understand fully what you mean. Do you, after a search, extract the PV
>from the hashtable? Then i see your point. But I save the PV when getting a
>value between alpha and beta anywhere in the search. The problem you are
>referring to gives me a 1 ply search hash value for the position, while
>otherwise I would have none at all. So when I have this position again, at least
>I have a 1-ply-best move to search first.

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