Tord Romstad wrote:No, killers are a very poor substitute for threat moves. The most important threat moves are usually captures and promotions, which (at least in most programs) are excluded from the killers.
And which are searched first, because of the good-captures-first ordering strategy... I've never gotten any sort of gain from this idea, although I can try it again with the current testing to get a pretty accurate measure of its effect...
I think you miss the point. The main purpose of keeping track of threat moves is not to use the information for move ordering, but to use it for decisions about move selection, reductions and extensions. When deciding what moves to prune or reduce, it is very useful to know what the opponent is threatening. The move that refuted the null move at the same node (which is what we call the "threat move" in this discussion) is a very natural thing to take into consideration. The most obvious example is if the threat move is a capture: In this case, it makes sense to not prune any move which defends the captured piece, or moves it to a safe square. I use this and many similar tricks in my "super-qsearch", the transitional phase of tapered selective search between the main search and the qsearch.
Tord
I would be interested in Bob's results of retrying it. It could be useful for both purposes, one never knows . In 90's I did lots of work on "super-qsearch" ideas which never turned out as great as I hoped. I think it is cool you found something that works well for you. Has anyone had success with these concepts?
Tord Romstad wrote:No, killers are a very poor substitute for threat moves. The most important threat moves are usually captures and promotions, which (at least in most programs) are excluded from the killers.
And which are searched first, because of the good-captures-first ordering strategy... I've never gotten any sort of gain from this idea, although I can try it again with the current testing to get a pretty accurate measure of its effect...
I think you miss the point. The main purpose of keeping track of threat moves is not to use the information for move ordering, but to use it for decisions about move selection, reductions and extensions. When deciding what moves to prune or reduce, it is very useful to know what the opponent is threatening. The move that refuted the null move at the same node (which is what we call the "threat move" in this discussion) is a very natural thing to take into consideration. The most obvious example is if the threat move is a capture: In this case, it makes sense to not prune any move which defends the captured piece, or moves it to a safe square. I use this and many similar tricks in my "super-qsearch", the transitional phase of tapered selective search between the main search and the qsearch.
Tord
I would be interested in Bob's results of retrying it. It could be useful for both purposes, one never knows . In 90's I did lots of work on "super-qsearch" ideas which never turned out as great as I hoped. I think it is cool you found something that works well for you. Has anyone had success with these concepts?
-Sam
We did this sort of thing in the last few versions of Cray Blitz. We had a "transition phase" between the full width search and the pure captures-only search, where we dealt with checks, and any other moves we thought might be on the edge of becoming "interesting". For example, most anyone would extend Bxh7+, but what if the black king is at h8? You are not forced to capture it, but if you don't you are a pawn down, so we chose to treat those two moves as the same thing in the transition phase of the search in CB...
I did this in early versions of Crafty, but removed it years ago. Might be worth revisiting since search depths of today are 2x deeper than 1995...
. In 90's I did lots of work on "super-qsearch" ideas which never turned out as great as I hoped. I think it is cool you found something that works well for you. Has anyone had success with these concepts?