Author: José Carlos
Date: 10:06:06 08/31/01
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On August 31, 2001 at 12:15:07, Robert Hyatt wrote: >On August 31, 2001 at 11:15:33, Steve Maughan wrote: > >>Bob, >> >>>>Or are you defining a PV search as any search that could result in a PV from >>>>the root? >> >>>Yes to your last question. This is a "hard" search to do, and without good >>>move ordering, it becomes harder still. Hence the internal iterative deepening >>>to help it out. >> >>OK. If this the case then can't you detect a PV node as: >> >> PV When (beta-alpha)>1? >> >>Regards, >> >>Steve > > >Not quite. This will think that when you are searching some non-PV move deep >in the tree, but below the first move at the root, and you fail high on that >move, you would have that case. I'm not sure (without thinking about it a lot) >that I want to trigger IID everywhere this happens. Right now what I do is >probably overly conservative... Here's what I do (dunno if it's any better): I have 5 search functions: - Pensar: which performs the iterative deepening, running a loop increasing depth until time is over, and calling PVS(depth). - PVS: which controls the search at the root. Performs a special move ordering and calls AlfaBetaPV (for PV move at the root) with aspiration window and AlfaBeta (for the rest of the moves) with Alfa,Alfa+1. It also controls fail high's and low's, and moving up or down the search bounds. - AlfaBetaPV: standard alfa-beta search with IID but not null-move. It calls AlfaBetaPV(Alfa,Beta) for the first move, and AlfaBeta(Alfa,Alfa+1) for the rest. Also, if any of these second moves fail high, it calls itself, AlfaBetaPV(Alfa,Beta) and checks if a new PV move is reached. - AlfaBeta: search function for the non-pv moves. It gets only a bound (Alfa) and sets a local variable Beta, which is Alfa+1. It doesn't do IID. It does null-move. It _always_ calls itself (AlfaBeta) with the actual Alfa. - QSearch: no need to explain this. This way, I always know where I am, and I can easily do different tasks (if I want) with PV and non-PV nodes. Hope this helps, José C.
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