Computer Chess Club Archives




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

Author: Christophe Theron

Date: 18:25:11 10/01/98

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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:
>>>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
>>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,
>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.


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