Author: José de Jesús García Ruvalcaba
Date: 08:28:11 11/22/01
Go up one level in this thread
On November 22, 2001 at 11:21:04, Gordon Rattray wrote:
>On November 22, 2001 at 10:48:01, Victor Zakharov wrote:
>
>>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.
>
>
>When you say "smartly", is this only something that a human can do? If not, why
>doesn't the program itself "step into" its mainline and then retract? Is it
>because of time issues? Or because it doesn't give a benefit often enough?
>
>I'm just a bit puzzled as to why "computer + human" can be better than just
>"computer", especially if we're not assuming the human has any great chess
>playing ability.
>
>Gordon
>
The "selective search" of a human, even if only of average strength, is
(usually) better than the selective search of the computer.
José.
>
>>
>>>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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