Author: blass uri
Date: 10:22:34 05/31/00
Go up one level in this thread
On May 30, 2000 at 18:11:51, Robert Hyatt wrote: >On May 30, 2000 at 15:24:36, Ed Schröder wrote: > >>On May 30, 2000 at 00:28:47, Robert Hyatt wrote: >> >>>On May 28, 2000 at 16:37:32, Gian-Carlo Pascutto wrote: >>> >>>>On May 28, 2000 at 10:02:05, Georg v. Zimmermann wrote: >>>> >>>>>From my tests it shows that it sticks with the hash-move about 50% of the time. >>>>>Should this number be higher ? >>>> >>>>Hmm...if this number is also effectively your 'move ordering percentage', >>>>which I assume it is, it is quite low. I'd expect it to be at least about 75%. >>>> >>>>> >>> >>> >>> >>>The classic definition of a "strongly-ordered tree" is this: If, for every >>>node where you fail high, you fail high on the first move at least 90% of the >>>time, then your move ordering is good." If you are much below 90% and already >>>have a serious problem that is not hard to fix. The traditional ordering ideas >>>holds Crafty at 92% and better for most of the game. >> >>I can't understand the 92%. A perfect mini-max search requires many many >>nodes an alpha-beta cutoff will not work and you are forced to search all >>the nodes of the ply in question. And this number is certainly much higher >>than 8%. > >You have to re-read the definition again, _very carefully_ to avoid the semantic >trap you just fell into. > >For every position where you fail high, if you fail high on the first move you >try, you increment a counter "right++". You always increment a counter "fh++". >When you finish the search, you compute percent=right/fh. That number needs to >be over 90% to consider your tree strongly ordered. Notice that this 92% number >(in crafty) simply says this: > > "if we look at _all_ the positions in the tree where the search fails high, > then 92% of those fail highs happen on the first move searched in that > position, which is known as 'optimal move ordering'. I do not agree that failing high on the first move is optimal move ordering. Here is an example: [D]8/6k1/rp3ppp/8/N7/8/4RPPP/6K1 w - - 0 1 My understanding of optimal move ordering is that after the moves Nxb6 or Nc5 the first move to search will be Ra1+(at least in cases that you are going to search more than few plies after these moves because Ra1+ Re1 Rxe1# is the faster way to prove that Nxb6 or Nc5 is wrong) If you start with taking the knight than your first move may fail high but you waste more time to prove that Nxb6 or Nc5 are wrong. Uri
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