Author: Bruce Moreland
Date: 00:03:24 01/04/98
Go up one level in this thread
On January 04, 1998 at 00:20:22, Don Dailey wrote: >I hate to open this can of worms but here goes: Are you saying that >the quies search of a deep searching program should be "constructed" >differently that a shallow searcher? I do not ask your opinion >because I agree or disagree, I'm trying to figure it out myself. > >And along the same lines, should the evaluation function be different? Very good questions. If you do a very shallow search you will miss very simple tactics. You could probably get a clue about what kind of tactics are killing you, and add some specific knowledge to try to avoid these situations. For instance, assume you have a white bishop on c4 and a white knight on e4, which are forked by a black pawn on d5, which is protected by another black pawn on e6. This has happened to you because black has just played d6-d5. With a two-ply search, you may walk into this situation. You play your bishop to c4, you see the reply ... d6-d5, but you don't have any good captures now so you end up returning the static eval for this position. So you make the move, your opponent says, "duh", and plays ... d5, and you notice now that your score is -2. I used to beat my Chess Challenger 7 with pawn forks all the time, even at one minute per move. Perhaps it could have benefited from some knowledge: If it is my turn to move, and I have two pieces en-prise to defended pawns, either give a penalty or extend, according to taste. I don't have anything like this in Ferret, and I have never detected a situation where this mattered. The problem with a 2-ply searcher is that these pawn forks represent a very simple form of persistent and effective threat -- it is here now, but you don't see it, and it will still be here when you finally do see it, and when you do see it there will be nothing you can do about it. So if you search two plies, and you encounter this situation, it will probably propagate to the root and kill you. If you search more plies, you can still mis-evaluate these situations, and they can still propagate to the root, if everything above the two plies at the tip was forced, but since I've never seen it happen I conclude that it is rare. Perhaps it would be more common for mis-evaluation of this situation to result in selection at the root of a move that is slightly worse than would otherwise be played. A 2-ply searcher would get a lot of practical benefit from detecting pawn forks, I think. I get the feeling that a 12-ply searcher would not benefit as much. If this is the case, then maybe it does make sense for the evaluation functions to be different. If adding knowledge, in one case, results in obviously better play, and in another case it only improves some freakish cases, then it seems likely that it's more important to add this knowledge in the first case, and less important in the second case. bruce
This page took 0.01 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.