Author: Robert Hyatt
Date: 20:03:08 12/08/00
Go up one level in this thread
On December 07, 2000 at 17:33:33, Bo Persson wrote: >On December 05, 2000 at 19:25:55, Scott Gasch wrote: > >[...} >> >>Finally, I changed the code to follow Ernst's advice... Before I was storing >>depth+extend as the depth in the hash node... now I am only storing depth. I do >>not fully understand this, though... if I just got a score X from a search with >>depth=depth+extend, is it incorrect to store depth+extend in the hash table? I >>would really appreciate some clarification of this concept if someone has time. >> > >The idea is to store the depth/draft you will have when you get back to using >the node, which is the remaining depth upon entry to search(). The fact that you >extend some branches and/or cut some with nullmoves etc, doesn't change teh >*nominal* depth remaining. That is what you will use in the probe, so that is >what you have to store! > > >>Let me describe one more thing (which I also learned from one of Bruce's >>messages, I think) so that someone can sanity check me if I am doing it wrong. >>When I get an exact score that is >= +MATE_IN_N or <= -MATE_IN_N I am converting >>it to a bound. I do this because a MATE_IN_N is relative to the depth of the >>position in the search tree... and if we come across the same position in the >>tree later at a different depth the score will be incorrect. >>So convert _exact_ scores >= +MATE_IN_N into lower bounds of MATE_IN_N -- that >>is, convert "this node is mate in N moves" into "this node is worth at least a >>forced checkmate". Convert exact scores <= -MATE_IN_N into upper bounds of >>-MATE_IN_N -- change "this position gets me killed in N moves" into "this >>position is a forced mate in some number of moves". I've also seen people >>adjust these scores relative to the current ply... I like the bound idea better >>because it is simpler. > >Yes, but the adjustment improves the scores. Again, the idea is to store a score >that is independent of the path taken to get there. You probably get a >mate-in-N-from-the-root, which you cannot score, as it is path dependent. If you >reach a mate-in-7 when you are already 4 plies down in the search, that is >stored as a mate-in-3-from-here (exact score). > >If you later hit the same position 6 plies down from the root, >mate-in-3-from-here is now a mate in 9. If you hit the position 2 plies from the >root, it is a mate in 5. > > >Bo Persson >bop@malmo.mail.telia.com One warning: adjust EXACT scores only. Do _not_ adjust bounds that just happen to be mate score bounds. That will wreck the search.
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.