Author: Chris Carson
Date: 12:05:52 09/28/98
Go up one level in this thread
On September 28, 1998 at 13:53:31, John Coffey wrote: >My understanding of alpha-beta is like this ... > >7 5 3 2 ? <--- some responses for black > \ | / \ | > 3 ? <--- some choices for white > \ / > \ / > ? <--- current position > >Having looked at the first choice and all of black's responses, we conclude >that the first move has a value of 3. We then try to determine the >value of the second move. We see that one of the black responses has a >value of 2, which is worse for white that the other choice of 3, so we >already know that the second branch is going to be worse than the first, >so we do not need to look at any more of the black responses, thus producing >a savings. > >I have some questions .... > >1. People are always talking about two values here, alpha and beta, but seems >like we could be just dealing with one value, the value that we are comparing >from the previous level. As a result I get confused when people talk about >"fail low" and "fail high." > >2. If doing a deeper search, then it seems to me that I would want to pass the >same value even deeper into the tree .... > > 2 ? ? <----- Black responses at depth=4 > \ |/ > ? ? <---- white responses to black responses > \ / >7 5 3 ? ? <--- some responses for black > \ | / \ / > 3 ? <--- some choices for white > \ / > \ / > ? <--- current position > > >In this case do we not look at the remaining black responses at depth =4 >beceuse the best white move branch at depth=1 is a 3? > >I have found some pseudo-code on the net. I will get that a closer look. > >Thanks, > >John Coffey Take a look at the following links: http://www.xs4all.nl/~verhelst/chess/ - click on "Chess Tree Search" http://www.npac.syr.edu/copywrite/pcw/node341.html - click on "Sequential Computer Chess" http://www.maths.nott.ac.uk/personal/anw/G13GT1/compch.html Best Regards, Chris Carson
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