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Subject: Re: Branching factor and parallel search efficiency

Author: Daniel Clausen

Date: 08:50:52 07/16/04

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On July 16, 2004 at 11:42:44, Eric Oldre wrote:

>On July 16, 2004 at 08:59:42, Tord Romstad wrote:
>
>>Which influence does the branching factor of a two-player, zero-sum game have
>>on the efficiency of a parallel search?  Is the speedup when using multiple
>>processors independent of the branching factor, or does the speedup increase
>>(decrease?) when the branching factor increases?  Intuitively I would expect
>>the speedup to increase with the branching factor, but I have no experience
>>with parallel search.
>>
>>In case it is not clear, when talking about "branching factor" above, I am not
>>talking about what is commonly called the "effective branching factor" (which is
>>typically in the range 2-3 for a chess program using recursive null move
>>pruning),
>>but about the average number of legal moves (around 30-40 in a typical chess
>>middle game).
>>
>>Tord
>
>Tord,
>I've heard alot about the top programs having a branching factor of 2-3. But I
>don't know how to measure this with my own engine, what statistics do people use
>to determine their branching factor.

AFAIK, most people just divide the time used for iteration N+1 with time used
for iteration N. You can also use visited nodes, but since you most likely
measure the time already, it's easier.

Sargon



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