Author: Robert Hyatt
Date: 06:57:43 08/24/99
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On August 24, 1999 at 05:39:54, Inmann Werner wrote: >Hello all! > >I am again trying to tune my program, and came to some questions. > >1) >What to do with fail lows and hashing. >Put them in for move ordering? I think no. > >Put them in for hash hits? >I do, but I am not sure, it is good. >If I get a hash with fail low flag I check, if it is again a fail low and only >then I use it. >That makes a cuttoff for easy, not disturbing? >But in positions, i get differences, if I use fail low hash hits. Not much, >but...? > >What do you think about doing best? > > >2) >It disturbed me, that in some not clear positions the search often switches, and >that only for 1 point better (1/100 pawn) which is not real relevant, but costs >much time cause of the research. >So I thought about making the eval result not so perfekt (score=(score/2)*2). >Now it switches not so often, but in "normal" positions needs more nodes (less >cutoffs?). > >Is this idea dumb or worth thinking about it. >Makes a small evaluation, where much values of different positions give the same >value the search slow? > >Werner I don't quite understand, but you have only three cases to handle: 1. When you complete a ply, and the score you found was > alpha and < beta, you store the score, and EXACT. If you later get a 'hit' and find this position, assuming the depth is sufficient, you just return value without doing any more searching at all. 2. When you get a fail-high at a node, you store the value you got (which was >= beta) along with a flag LOWER (to note that this is a lower bound on the score, that it might actually be higher than this). When you get a hit on this type of entry, you only need to verify that your current beta value is < the bound stored in the table, and if so, you return the table value without searching further. 3. When you get a fail-ow at a node, you store the value (alpha or less) and a flag UPPER (this is the best you can do, the worst score possible could be even lower). When you get a hash hit, and your current alpha value is > the table bound, you just return the table bound with no further searching. That's all there is to it...
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