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Subject: Re: Returning PV from hash table

Author: Uri Blass

Date: 22:05:03 01/15/03

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On January 16, 2003 at 00:09:04, Nathan Thom wrote:

>On January 15, 2003 at 22:59:57, Uri Blass wrote:
>
>>If you use hash tables but not for pruning you can always get the entire pv.
>>Movei still does not use hash tables for pruning but only for order of moves
>>because the last time that I tried using hash tables for pruning test positions
>>showed that the result is not better.
>>
>>One possible reason is the fact that I do not store partial extensions in the
>>hash tables(I thought that it still may be better to avoid search and use the
>>result at depth k to prune expensive search at depth k+partial but tests showed
>>that it cause more problems).
>>
>
>I dont understand how using hash tables for pruning would not speed the search?

I can get the same depth faster but I get less correct results in the same time
because I get less solutions correct.

>
>>Another possible reason is my different pruning methods that mean that I do not
>>always get the same result when I search the same depth from the same position
>>even when the partial extensions are the same(it is the same for everybody who
>>use repetition detection but I have more reasons).
>
>I also dont understand why you dont get the same result when searching the same
>position to the same depth each time. What does repetition detection do to
>affect this?

Repetition detection means that the score is not based only on the position but
only on the history of the game.

You can get a draw score for position because of repetition in one line and not
get a draw score in a second line because in a second line you cannot force a
repretition of a previous position so if you store a draw you return wrong
score.

My pruning and extensions are also based on other factors that are not the
position that is on the board.

Usually the advantages of pruning based on hash tables are bigger but it seems
that it was not the case for Movei in the last time that I tested.

Uri



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