Author: Heiner Marxen
Date: 14:02:51 12/31/00
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On December 31, 2000 at 10:56:07, Steve Maughan wrote: >Bob, > >>>Surely at least when alpha is raised this is equivalent to finding a new best >>>move and hence the PV needs to be cut off? >> >>I don't think so. I don't do this in Crafty, yet I raise alpha and lower beta >>just as you do. All the hash entry says is "this position should have a higher >>alpha bound (or lower beta bound)..." but it says nothing at all about a PV >>since you still have to keep searching... > >As an example, suppose that initially Alpha = 1.00, Beta = 5.00 . From the hash >we find a deeper search with a lower bound of 3.00. It is possible that had we >not changed alpha and after the node has been searched the score for this node >would be +2.00 and it could have formed part of the PV. I don't follow here: you just stated that the TT says "this node's value (for this depth) is 3.00 or even higher". And we are trusting the statements from the TT, right? So, we expect a search here to not return anything below 3.00, especially not 2.00 as value. While it is quite possible for a search to contradict the bound stated in the TT, this is due to the nature of the TT to accumulate more and more depth/info. But the whole point of the TT is to _not_ search for a hit. Am I confused? > However, if we raise >alpha to 3.00 the search will fail low and therefore the node cannot be part of >the PV. This doesn't seem right. Am I missing anything? A fail low is not just now part of the PV. After a research with wider bounds it may become part of the PV. Heiner >I'll have a fiddle with my code and see if I come to any conclusions. > >Regards, > >Steve
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