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

Author: Tijs van Dam

Date: 02:55:39 02/01/00

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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.

Tijs



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