Author: Tony Werten
Date: 00:50:52 04/21/04
Go up one level in this thread
On April 20, 2004 at 21:33:01, Robert Hyatt wrote: >On April 20, 2004 at 20:25:56, Sune Fischer wrote: > >>On April 20, 2004 at 15:57:20, Pallav Nawani wrote: >> >>> >>>>So, Dr. Hyatt, what you're calling a LOWER flag is (I think) what I'm calling >>>>HashFlagBeta, and what you're calling UPPER, I call HashFlagAlpha, becuase those >>>>were the bounds that were exceeded. Personally, I hate this terminology...I wish >>>>we'd use more friendly terminology like AtLeastThisScore or LessThanThisScore. I >>>>think when I rewrite Trueno I'm going to do that, now that I understand >>>>alphabeta a little better. But that's neither here nor there...how does this >>>>look? Andrew >>> >>>This confused me a *lot* when I was programming my engine :-) I read beowulf's >>>code and I saw UPPER/LOWER. I read Bruce Moerland's page and I saw >>>HashBeta/HashAlpha. Only after much distress was I able to sort it out. >>> >>>But I could not figure out how hash entries could be use to avoid NULL move. >>>How do I do that? >> >>If you have reason to believe a null move will fail-low, for instance >> >>if (flag==UPPER && score<beta) >> do_null = "not recommended"; >> >>I use depth>=current depth. >>If I read the code correctly then Crafty uses depth>=current depth - R >>It seems theoreticly wrong, at least the way I do probes and stores. >> > > >Why? You want to know whether the null search will likely fail high or low. It >is going to be done to depth-R so why can't you use that in the test??? > >I don't see anything "theoretically wrong" with that... I am going to do a >search to depth-R, and if this hash entry suggests that such a search of a >_real_ move will fail low, then not playing a move will be even worse... No >point in even trying the null-move. > >This was all explained in the Campbell null-move search paper years ago. >Everyone I know does it this way. Bruce, etc... Writing it out makes it more clear. For simplicity R=2 Depth left: 5 normally: WBWBW after nm: BW 1 move for black left after nullmove so draft has to be 2 ie depth-(R+1) Depth left: 6 normally:WBWBWB after nm: BWB 2 moves left for black so draft has to be 4 ie depth-R So R is always safe, and when there is an odd depth left, you could use R+1. Tony > > > > > >>-S. >>>Pallav
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