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Subject: Re: Nodes per second........

Author: Peter Fendrich

Date: 10:42:04 10/02/98

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On October 01, 1998 at 21:25:11, Christophe Theron wrote:

>On October 01, 1998 at 17:54:48, Jim Phillips wrote:
>
>>On October 01, 1998 at 08:25:15, Roberto Waldteufel wrote:
>>
>>>
>>>On September 28, 1998 at 11:28:42, Peter Fendrich wrote:
>>>
>>(snip)
>>>
>>>>Sure, winning games is better than losing them... :)
>>>>Search does in fact have some good effects by itself...
>>>>There was an intresesting article in ICCA Journal a few years ago. I don't
>>>>remember any details about the authors and such but here is what I remember from
>>>>the article.
>>>>They played two programs against each other with completely random evaluation.
>>>>One program searched the tree, gave the leafs a random evaluation and and backed
>>>>up the values in an alfa/beta manner. The other program just gave each move from
>>>>the root a random evaluation. The first thoughts about a match like this is that
>>>>the result will be as random as the evaluation code, but it wasn't!
>>>>The results showed that the tree version was better because of a tendency to get
>>>>more space just because of the tree search itself. Well, my memory is fading
>>>>here...
>>>>
>>>>//Peter
>>>
>>>Maybe the tree version would find shallow mates, and the root version would not?
>>>I think this might well account for the difference.
>>>
>>>Best wishes,
>>>Roberto
>>
>>I'd like to throw in my 2 cents....  If you choose a move at random from
>>the "leaf" nodes, you are going to tend to return to a root move that
>>generates a "bushier branch".  Let's say you have three possible root
>>moves, and you search two plies deep and choose a move at random.  If
>>there are 10 "leaves" corresponding to the 1st root move, 20 leaves
>>corresponding to the 2nd root move, and 70 leaves for the 3rd root move,
>>there is a 70% chance that your random function will choose the 3rd root,
>>which is the one that will also lead you to a more open position with a
>>lot of possible moves to make.  The program that simply chooses a move at
>>the root at random has only a 33 1/3 % chance of picking the 3rd root....
>>Does this seem reasonable, or am I off around Jupiter?
>>-Jim Phillips
>
>You are absolutely right. The random evaluation in fact turned out to be a way
>to find the moves that lead to more mobility.
>
>Both programs were able to find shallow mates. This was not the issue here.
>
>
>    Christophe

Correct!
And this is the article:
Levene, M. and Fenner, T. (1995).
     A Partial Analysis of Minimaxing Game Trees with Random Leaf Values.
     ICCA Journal, Vol. 18, No. 1, pp. 20-33. (A)

The article is a continuation from:
Beal, D.F. and Smith, M.C. (1994).
     Random Evaluations in Chess.
     ICCA Journal, Vol. 17, No. 1, pp. 3-9. (A)

//Peter



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