Author: Robert Hyatt
Date: 08:13:46 08/22/02
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On August 22, 2002 at 05:26:45, Gian-Carlo Pascutto wrote: >On August 21, 2002 at 18:01:06, Robert Hyatt wrote: > >>No I don't. I have a _classic_ definition of forward pruning: >> >>To selectively discard some moves while keeping others. >> >>Razoring doesn't do that. It simply reduces the tree depth by 1 ply for >>some branches. Just like null-move. Neither of which are selective forward >>pruning in any book you might check... >> >>The effect is admittedly somewhat similar in that the size of the tree is >>different. But with forward pruning you throw moves out based on some >>a priori knowledge and once you throw them out, they are _out_. Reducing >>the depth is _not_ the same thing, because you _still_ give the move a chance >>to do something... > >Reducing the depth is throwing out moves at the bottom end, not the top >end. It's exactly the same thing, it just works at the other end of the tree. > >-- >GCP It isn't "exactly the same thing". Sorry. But since I have to teach an AI course here, I have learned to speak _precisely_ to avoid confusion in this area. Forward pruning is one thing. Depth-reduction is something else entirely. If you don't see the difference, pick up any good AI book. Most all cover it. Reducing the depth is reducing the depth. It is not the same thing as saying "I choose to throw this move out at this ply and not even consider it at all". razoring says "this move looks suspiciously bad. Rather than just throwing it out, I am going to search it to a 1-ply reduced depth, so that if it _does_ do something good, I will have a chance to see it with the reduced search." Those are _not_ the same thing. They produce the same _effect_. That of making the tree smaller. But they are _not_ the same thing at all... Forward pruning will result in outright blunders. By pruning a single move you miss the fact that that move kills you. Or kills your opponent. Even if the threat is very shallow. Razoring doesn't hide the shallow threat at all, which is the point...
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