Author: Bo Persson
Date: 03:24:18 08/31/02
Go up one level in this thread
On August 30, 2002 at 18:42:40, Omid David wrote: >On August 30, 2002 at 17:39:27, Gian-Carlo Pascutto wrote: > >>On August 30, 2002 at 17:37:25, Patrik wrote: >> >>>Difference is that Crafty used alpha instead of value when it re-searches. >>>Is there any reason to use alpha instead of value? >>>Using value which is greater than alpha seems to cause more cutoffs than using >>>alpha. >> >>If you get a fail high on the first search and a fail low on the second (*), >>you will lose your PV's. This does not happen if you do the research with >>alpha. >> >>(*) If you think this can't happen, you haven't been doing chessprogramming >>long enough. >> >>-- >>GCP > >If you take a look at Aske Plaat's PhD thesis "Research Re: Search and >Re-search" and his numerous other publications, you'll notice that on many >occasions his results are not substanciated enough in practice. > >For example he conducts all his experiments (on 20 test positions, depth 8) in >brute force fixed depth search, which is extinct nowadays (even in 1996, who >didn't use a form of variable depth search?). > That was done to get numbers that were easy to compare (I think he says so too). If you have extensions and pruning in the tree, *any* changes to the tree will affects its size. Even a seemingly random event in the search can get an extension triggered or not. So to have a stable base for his measurements, he disabled most stuff, and ended up with a fixed depth search. This somewhat reduced the usefulness, but it *did* produce a result. I have seen that a simple thing like recoding quicksort for the move list can affect the tree size by 50% in one particular test position. The sorting was still correct, but moves with the same preliminary score ended up in a different order. Bo Persson bop2@telia.com
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