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Subject: Re: Q. Aspiration, PVS, Fail-Soft

Author: Uri Blass

Date: 14:56:40 07/02/04

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On July 02, 2004 at 17:22:15, Scott Gasch wrote:

>On July 02, 2004 at 12:28:31, Fabien Letouzey wrote:
>
>>On July 02, 2004 at 12:07:42, Volker Böhm wrote:
>>
>>>On July 02, 2004 at 09:21:41, Fabien Letouzey wrote:
>>
>>>>Bruce makes a slightly different assumption that depends on the
>>>>window.  IMO it is an uncommon implementation but it might be better
>>>>depending on aspiration windows.
>>
>>>What does Bruce suggest? Btw. who is Bruce, Bruce Moreland?
>>
>>Yes Bruce Moreland.  His tutorial is famous, but it seems his description of PVS
>>is not the commonly-used algorithm:
>>
>>http://www.seanet.com/~brucemo/topics/pvs.htm
>>
>>Fabien.
>
>Bruce's tutorial doesn't start to search with a minimal window until it find a
>PV node (i.e. until a score returned beats alpha).  What if you are on, as bruce
>calls it, an "alpha node" (where everything is gunna fail low)?  If your move
>ordering is good then you should still search the best move first.  Therefore
>you can speed things up even more by searching the rest of the moves with a
>minimal window (the thought being that they are all worse than the first move).
>Bruce's implementation searches all of these moves on alpha..beta if one has not
>yet beat alpha.  Maybe it's blasphemy, but I think the "traditional" PVS
>implementation is better, assuming you have a good move order.
>
>Scott

I do not understand why you assume that your move ordering is good after a fail
low.

Suppose that you have a  big fail low that means that you cannot save the game
after the first move in your move ordering(suppose score of more than 4 pawns
against yourself.

It means that there are 2 possibilities:
1)You cannot save the game(what you do is not important)
2)You can save the game by a better move(in this case I suspect that it may be
better to use bigger window for the other moves in order to save the research
for other moves).

I do not do it today but it may be a good idea to try it.

Uri



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