Author: Victor Zakharov
Date: 07:48:01 11/22/01
Go up one level in this thread
On November 22, 2001 at 09:42:36, Robert Hyatt wrote:
>On November 22, 2001 at 05:27:05, Gordon Rattray wrote:
>
>>The Fritz GUI analyses games ("Full Analysis") by starting at the end of the
>>game and retracting moves. How does this compare to going forwards? Does it
>>produce better results?
>>
>>I think this issue has been discussed before, but my search has failed to find
>>anything. Please feel free to forward me a past link if appropriate.
>>
>>Gordon
>
>
>Here is the idea...
>
>If you start at the end of the game, you load the hash table with stuff
>that will help as you search at earlier moves... with the "idea" that
>earlier analysis will be more accurate since it will have access to these
>scores.
>
>It doesn't work however.
It worked Ok in a lot of situations I have met.
>IE pick three points in the game, (a) where a key mistake is made, (b) a
>position further into the game, and (c) a position near the end where the
>program can see that it is lost. As you search backward, when you reach
>(b) the search might well _still_ see that it is lost, because of the persistent
>hash entries that help. But when you back up past (b) eventually the
>hash entries get replaced, and you "lose the key scores". You don't find the
>_real_ place where you screwed up (a), instead the score seems to drop at
>(b) which is the wrong place.
I don't understand why engine must lose "key scores". It depends on the program
that analyzes position. Tiger14/Gambit-II (at least in CA interface) remembers
score quite Ok in similar analysis. Don't forget that not only "hash table"
keeps the history. Most engines remember what moves lead to good/bad evaluation
and tried to use them first/last in a search. Hiarcs is very good in similar
learning. (However it loses hash tables values quickly). Tiger is more perfect
here.
The real problem is when the program thinks that it found a better move with
better score, but really it is mistaken. So experienced chess players make the
new move and continue the line. Sometimes a program is able to find that it is
wrong and finally bring the score to the point (a).
Sometimes it fails. But method really works and people that use it smartly can
get large advantage.
>Since neither way finds the actual mistake, I don't like the back-to-front
>approach because if you do search front to back you will find the "mistake"
>at a different place, which is nothing more than confusing.
I don'y state that usual front-to-back analysis is bad. Both have advantages and
lacks. And nothing bad that two approaches can give different positions where
mistake took place. Just analyze both positions more deeper (and interval
between them). And you will find the truth.
Victor
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