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Subject: Re: Exponential explosion of alpha-beta trees

Author: Dann Corbit

Date: 16:08:30 07/05/02

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On July 05, 2002 at 17:36:11, Omid David wrote:
[snip]
>If as you pointed out the programs reach the depth of 50 plies, I believe most
>of the games will end in a draw.

Sounds like a hunch to me.  I wonder if any experiments have been run to see if
we get the same drop off in computers that we do in GM's.  I suspect that with
the GM's they are deliberately drawing once they get some small advantage.

>But I don't see alpha-beta based programs reach even the depth of 20 plies in
>next 50 years!!! No matter how fast the hardware will be, it won't match the
>exponential explosion of alpha-beta trees.

Most modern programs get anywhere from 10 to 15 plies on a reasonable search
(say G/90 on fast hardware).  Let's take the pessimistic estimate of 10 plies.
That means we need ten more plies.

CPU speed doubles every 12 months (used to be once every 18 months so it is
accelerating).  But we will use the pessimistic figure of 18 months.

Suppose a branch factor of 4 (many computer programs do better than that).

Two doublings buys us a ply.

We need 20 doublings to get ten more plies.

So in 20 years, the average computer program will search 20 plies (even from the
most difficult positions).

I suspect it will be a lot sooner.



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