Author: Robert Hyatt
Date: 09:33:36 04/21/04
Go up one level in this thread
On April 21, 2004 at 04:44:31, Sune Fischer wrote: >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??? > >Okay, so you are comparing the depth of a nullmove search to an upper score of a >full search, and not to a fail-low of a nullmove!? > >Yes that might make good sense I suppose. > >I thought it was a problem that the nullmove search at depth-R would have been >to depth-2*R, so those two can't be compared. > >-S. Right. The question is "will a null-move search likely fail high here?" If the answer is yes, it is a cheap search. But if a normal search to that reduced depth will fail low, clearly a null-move search will likely be even worse and there is little point in trying it. > >>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... >> >> >> >> >> >>>-S. >>>>Pallav
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