Author: Ed Schröder
Date: 03:26:05 03/08/01
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On March 08, 2001 at 06:17:40, Ulrich Tuerke wrote: >On March 08, 2001 at 05:08:03, Matt McKnight wrote: > >>oops, messed up that last post... >> >> I've been toying with some move ordering ideas, and I would like to hear some >>feedback on them. >> >> First idea: >> Inspired by the killers list, I tried keeping a list of two moves per ply >>that seemed to be bad ideas, (score < alpha) and using that to sort those moves >>in the future to the end of the list. This seems to give me a small gain. Is >>this idea good, or will it cost me in some positions? >> >> Second idea: >> Along with the history heuristic, how about sorting moves by the >>positional gain they make? For instance: >> score += piece_eval[to] - piece_eval[from]; >> >>this also seems to help a little. Again, is it helping or not? >> >>Also, are these ideas dumb and old? > >At least, your 2nd idea is not new. It has been tried in an old gnuchess >version. I don't know if it's still used by the more recent versions of gnu. > >IMHO, the drawback is that you have to evaluate in addition to the leaves also >the inner nodes in order to get these piece values. I experimented a bit with >this, but I didn't make a thorough analysis. Since I seemed to observe that the >gain from improved move order (which is there IMO) is not really worth the >performance loss by evaluating all nodes, I decided not to use this. > >However I guess that your suggestion may deserve more attention. > >Uli The second idea to sort "the remaining moves" by a piece_square table has been in Rebel from the very early start. Last time (about 2-3 years ago) I removed the algorithm (just to satisfy my curiosity) Rebel's performance in ply-depth decreased with a factor of 2. Surprised by the outcome I quickly activated the algorithm again. Ed
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