Author: Robert Hyatt
Date: 06:58:45 08/01/03
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On August 01, 2003 at 02:33:13, Ross Boyd wrote: >Hi all, > >I want to get a clear definition of hash table bounds... > >So, this is what I understand... > >When we get a score during search, one of 3 things can happen: > >1. The score is >= beta... so we store this as a LOW_BOUND. >2. The score is <= alpha... so we store this as a HIGH_BOUND >3. Or its between alpha and beta... so its an EXACT score. > >So the definition of an EXACT score is anything we find between alpha and >beta... > >So far so good.... > >Ok, what about an EGTB probe? A successful EGTB probe returns a true score >whether it be a draw or the number of moves to mate. You are mixing apples and oranges. Suppose you get a hash hit with an EXACT indicator, but it is outside the alpha;/beta window. What would you store for such a position later? Answer = EXACT. Because it is an exact score. An EGTB hit is the same. It is not the result of an alpha/ beta search below this position with the current bounds in force, it is the result of a _complete_ search from this position. Complete searches always produce EXACT scores. Searches with an alpha/beta bound to speed up the search only produces an EXACT score when the score lies within the alpha/beta window. > >By applying the 3 rules above I SHOULD store the EGTB score as a LOW, HIGH or an >EXACT bound... Is that correct? No. EGTB hits are _always_ EXACT. > >Why not store it as an EXACT score? (Its as exact as you're going to get...) >Will the ab search break in some subtle way if I do this? > >I'd like to understand this once and for all.... > >Thanks for your comments!! > >Ross
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