Author: Ed Schröder
Date: 01:06:33 09/27/04
Go up one level in this thread
On September 26, 2004 at 19:03:53, Stuart Cracraft wrote:
>On September 26, 2004 at 04:30:44, Ed Schröder wrote:
>
>>On September 26, 2004 at 00:51:17, Sergei S. Markoff wrote:
>>
>>>Some ideas on hash move extensions.
>>>The idea was invented independently by Shpeer, Rybinkin ("Mirage") and me. In
>>>most cases this is a good idea to extend TT moves to improve search stability.
>>>But what scheme will be best for doing it?
>>>
>>>In ST the method is a little curious.
>>>
>>>TT_extesion_amount=INCPLY/RootDepth (in plies).
>>>while(TT_extesion_amount*RootDepth<INCPLY) TT_extesion_amount++;
>>>
>>>Anyway it improves play of ST.
>>>
>>>I need your results to compare.
>>
>>Since Rebel 12 I am using this:
>>
>> in case of (2 consecutive best_move_from_hash_table
>> && alpha < hash_table_score + margin)
>> then { extend with one ply in case this situation happens x times }
>>
>>Notes:
>>
>>. margin is currently set to 1.00
>>. x is currently set to 4, 8, 12, 16 etc.
>>. alpha in Pro Deo's philosophy could be beta in yours.
>
>I tried this -- hopefully I did it. If 2 consecutive hash table
>probes give a best move and beta < hash_table_score_returned + 1 pawn
>then extend.
>I assume your ply increment is in 1/4 hence the 4? so I am not sure
>I did it right.
Yes.
I can do 1/10, 1/9 .... 1/4, 1/3, 1/2, 1/1 parameter driven. I can set a maximum
too. I currently use 1/4 and no maximum, thus unlimited extensions. When I set
the paramter to 1/3 the slowdown is 15% and in comparison to 1/4 that's not
worth it for my engine. 1/4 works best for me. I still must try 1/5.
>My extension is based on things like extend+=0.25, extend+=0.50, extend+=0.33
>etc. so floating point. And mine simply does this:
>
>If 2 consecutive hash table
>probes give a best move and beta < hash_table_score_returned + 1 pawn
>then extend to a max of 1 ply.
>
>I tried this on my standard suite and saw no improvement but not something
>good must be there -- what should I be looking for to confirm positive effect.
The right tuning will depend on the (amount of) other extensions you are using.
The first time I tried the idea of hash-extensions was 10 years ago and there
after several other failed attempts. Patience and perseverance are key
ingredients improving a chess engine.
My best,
Ed
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