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Subject: Re: Returning PV from hash table

Author: Uri Blass

Date: 19:59:57 01/15/03

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On January 15, 2003 at 18:50:29, David Rasmussen wrote:

>On January 15, 2003 at 18:38:38, Nathan Thom wrote:
>
>>I just realised that my program LittleThought (in progress, hoping noone has yet
>>used this name?) only stores the best move in the hash table, so when a hash hit
>>occurs it cannot display the entire PV for that depth like everyone else's seems
>>to.
>>
>>Do you all store the entire PV in the hash entry? or some other trick im
>>missing?
>
>No one stores the pv, it takes to much space.
>
>In general, you can't always get the entire PV if you use hashing, and you do if
>you want a serious program.

Only if you use the hash tables for pruning.

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).

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).

When I decided to prune only when the depth is bigger and not equal to the
reported depth I also got slightly worse results(usually I was slightly faster
but there were still few cases when I got the solution one ply later).

Maybe the fact that I got slightly worse result was bad luck but I prefered
simply not to use hash tables for pruning because I have no time to check if
this is a small improvement or not a small improvement.

I am not going to change it for the cct5 because it is not something that I can
change in the last minute and it is more important for me to add better
evaluation of king safety and maybe better eval of pawn structure(not sure if I
will do it).

Uri



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