Author: Pat King
Date: 07:49:36 11/28/00
Go up one level in this thread
On November 27, 2000 at 13:01:04, Scott Gasch wrote: >Hi all, > >I have a standard AB search in my engine right now. It works fine and I am >reasonably happy with the tree sizes it is searching. > >However I am trying to convert it to a PVS -- a search with a minimal window for >all moves after the first followed, if needed, by a research with the full >alpha-beta window if this minimal window search returns a score in the original >a-b range. > >As a test I ran the original A-B search from d2d4 d7d5 e2e4 e7e5 to 8 ply and >compared the number of nodes searched to the new PVS search. I am pretty sure I >have the PVS implemented correctly and can only assume that the great difference >in tree size comes from a poor move ordering on my part: Another possible cause is an unstable evaluation if you haven't implemented quiescent search yet. I was surprised at how poorly MTD performed when I first implemented it, and surprised again how much better it worked with qsearch, even counting the extra qsearch nodes! PLY AB MTD MTD & Q 1 58 60 60 2 559 584 586 3 1731 1780 2055 4 19152 19262 10424 4 163049 182122 39425 6 572897 485609 176127 The above was performed from the initial position. Zotron uses hash, captures, and noncaptures for ordering. I now feel that anyone planning on implementing PVS or MTD, or any algorithm involving researches, should take the time to implement qsearch, or maybe SEE, first. > > AB PVS >1. 45 83 >2. 525 646 >3. 3004 4975 >4. 14061 23048 >5. 43460 147922 >6. 183094 633827 >7. 486054 4727636 >8. 1129783 11029952 > >The strange thing is that I am using the same move ordering in both cases: hash >move (with PV stuffed), winning captures (MVV/LVA), losing captures (MVV, LVA), >killers (beta cutoffs at same ply), rest sorted on history heuristic (depth^2). > >I've read that some people who use a SEE put losing captures at the end of the >list. I do not want to do this for two reasons: 1. I generate all captures >before any of the moves to maybe get a cutoff with less work done and 2. Because >I do not use a SEE I am not entirely certain that a MVV/LVA capture is indeed >"losing"... the opponent's piece may be hung and no recapture occur. > >Is this move ordering scheme sane? > >Thanks, >Scott You're welcome. Pat
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.