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Subject: Re: The Code for the Rybka-Mate-Bug

Author: Vasik Rajlich

Date: 00:50:48 12/15/05

Go up one level in this thread


On December 14, 2005 at 19:25:38, Dann Corbit wrote:

>On December 14, 2005 at 19:18:28, Uri Blass wrote:
>
>>On December 14, 2005 at 18:53:21, Dann Corbit wrote:
>>
>>>On December 14, 2005 at 08:00:00, Vasik Rajlich wrote:
>>>
>>>>On December 14, 2005 at 04:44:15, Steve Maughan wrote:
>>>>
>>>>>Vasik,
>>>>>
>>>>>>The problem is when the hash entry ages.
>>>>>
>>>>>This is easy to get around - just store the distance to mate from the *position*
>>>>>(i.e. not the root) in the hash table.
>>>>>
>>>>>In pseudo code:
>>>>>
>>>>>procedure push_hash(position)
>>>>>begin
>>>>>	if winning_mate_value_in_hash then
>>>>>		hash_draft_depth += position's_ply_from_root
>>>>>	else if losing_mate_value_in_hash then
>>>>>		hash_draft_depth -= position's_ply_from_root
>>>>>	store(position)
>>>>>end;
>>>>>
>>>>>procedure probe_hash(position)
>>>>>begin
>>>>>	if found_in_table(poistion) then
>>>>>	begin
>>>>>		get_hash(position)
>>>>>		if winning_mate_value_in_hash then
>>>>>			hash_draft_depth -= position's_ply_from_root
>>>>>		else if losing_mate_value_in_hash then
>>>>>			hash_draft_depth += position's_ply_from_root
>>>>>	end
>>>>>end;
>>>>>
>>>>>I hope this helps!
>>>>>
>>>>>Regards,
>>>>>
>>>>>Steve
>>>>
>>>>Steve,
>>>>
>>>>thanks, I guess this also works - although it's a bit dirty.
>>>
>>>What's the other way to do it?
>>
>>see my post in
>>
>>http://www.talkchess.com/forums/1/message.html?470096
>
>Can't the same position (therefore) have a huge number of different scores then
>(depending on where we saw it in the tree)?
>
>Tbis way seems more complicated to me.

True, you might not play the absolutely shortest mate this way - but you will at
least constructively hone in on some mate. The real problems come when the mate
scores are changing from one move to the next. (Or when the mate scores are all
the same :)) Then the engine will keep changing its mind about which mate it
likes.

Actually this whole mating technique thing is - well, it's just not chess. The
opponent should just resign (like in my tests he always does) :)

Vas




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