Author: Tony Werten
Date: 02:09:59 08/01/03
Go up one level in this thread
On July 31, 2003 at 18:15:47, Robert Hyatt wrote: >On July 31, 2003 at 14:23:34, Tony Werten wrote: > >>On July 30, 2003 at 17:18:12, Rick Bischoff wrote: >> >>>>> >>>>>a. at depth 3- hash table is empty for this position. alpha = -INF, beta = +INF >>>>>a. all requirements for null move are met >>>>>a. makes null move: int e = -alphabeta(depth - 3, -beta, -beta +1); >>>>> >>>>>b. now we are at depth 0, alpha = -INF, beta = -INF + 1 >>>>>b. we call quies(alpha, beta) >>>>> >>>>>c. e = static eval is, oh say, 1. >>>>>c. e >= beta, return beta >>>>> >>>>>b. store this position in the hash table as -INF + 1, exact, depth = 0, return >>>>>-INF + 1 >>>> >>>>This is _way_ wrong. How can it be "exact"??? It is impossible for the >>>>search to return valid scores outside alpha/beta window as defined at the >>>>root. If you are returning an "edge" then it must be an upper or lower >>>>edge, not an exact score. >>> >>>Yes, I know it is wrong-- which is why I was asking the question to begin with >>>:-) What I do know is store anything quies returns as exact-- but you are >>>telling me I can't do that, right? (Forgive my ignorance!) >> >>You are correct (despite what the others say), but only if you use the failsoft >>version of alphabeta. >> >>Tony > >I don't see how he can be correct even with failsoft. If you get a score >outside alpha/beta it is _never_ an exact score, it will only be a bound. No it isn't. If you evaluate and take a beta cutoff, the evaluationscore is still exact, has nothing to do with bounds. If you evaluate below beta then there are 2 possibilities. In the end, best score didn't improve, score is still eval, and eval is exact. Second, bestscore did improve, must have been by search, so read from start, but now 1 ply deeper. Tony
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