Author: J. Wesley Cleveland
Date: 11:16:24 06/05/01
Go up one level in this thread
On June 05, 2001 at 11:52:24, Robert Hyatt wrote: >On June 04, 2001 at 23:52:03, J. Wesley Cleveland wrote: > >>On June 04, 2001 at 23:13:33, Robert Hyatt wrote: >> >>>On June 04, 2001 at 17:00:10, J. Wesley Cleveland wrote: >>> >>>>On June 01, 2001 at 13:59:11, J. Wesley Cleveland wrote: >>>>I have been thinking about fail high's and fail low's. If you have a fail high, >>>>and you have used a significant portion of the time available for this move (> >>>>25% ?), you should just make the move without further searching, as you will not >>>>have time to resolve the fail high and investigate other moves anyway. >>>> >>>>Fail low's are a different problem. When you get a fail low, what you know is >>>>that the current move has an upper bound at ply n of the ply n-1 value - window >>>>while all other moves have an upper bound at ply n-1 of the ply n-1 value. It >>>>seems it might be better to search some of the other moves before re-searching >>>>this one. >>>> >>>>This leads to a crafty question. In search.c, if all the values are < alpha (a >>>>fail low), the value returned is alpha and not MAX(values). Why is this ? >>> >>> >>>Why does it matter? The value you get back is totally useless. Because >>>everything cut off low on the alpha value. >> >>Is not the value you get back an upper bound for that subtree ? If you return >>and save that value in the hash table, if you later get a fail low closer to the >>root, you may not need to re-search this subtree. > > >I don't save root-move scores in the hash table. I can't. That is not what I meant. Let me give an example. Say you are searching the first move with a window of (.4, -.4). One move at ply 3 drops a queen and has an upper bound of -8.2. Your search fails low, you re-search and establish a lower bound of -.55. You re-examine the move that loses a queen. The value in the hash table is the old alpha (-.4). If you had saved the true upper bound, you would not need to re-search.
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