Author: Robert Hyatt
Date: 14:08:03 08/02/02
Go up one level in this thread
On August 01, 2002 at 19:40:17, Martin Bauer wrote: >On August 01, 2002 at 08:12:13, Ulrich Tuerke wrote: > >>In order to get exact values, you in principle have to switch off alpa-beta at >>ply 1. But that's too expensive in terms of search tree sizes. > >Ok, thank you and all other people, who replyed to my question. I see it is not >so easy, I have to spend some extra work and be careful, that it does not waste >too much time. > >I dont want to trust the values at depth 1, because that is not a good look >ahead. > >>I do a pure minmax search at iteration #1. So, I get exact values at this level. >>These values - combined with other criteria - are some measure whether the best >>move is "an easy one". > >What about this Situation: I can recapture the queen in 1, but there also is a 7 >move combination that wins two rooks. So a 1 ply search would say "easy move" >because it only sees the recapture of the queen. But in truth there is a >slightly better move that wins 2 rooks, what gives a little bit better value in >my program and I think in most others, too. > >if I half the search time in a 1min bullet game, I may be blind for the better 7 >move combination, because of the reduced time. That is the reason, why I want to >ask for the difference of the two best moves with values resulting from depth 7. >Can ply 1 + some extra things replace ply 7. Or do I worry about things that >doesn't matter in practice? On what depends searching more or less in top >Engines? > >Bye > >Martin \ Here is what I do in Crafty: 1. I order all the root moves. To do this, I make each root move and do a captures-only q-search after each move to get a rough idea of the material situation on the board. 2. If one move is better than all the rest (by at least 2.0 pawns) then I set the "easy move" flag. 3. I then start the normal search. 4. If, during the search, this move "fails low" at any point, "easy move" is cleared. If, during the search, another move becomes best, "easy move" is also cleared. 5. When I have used 1/3 of the target time, and easy move is still set, I stop the search early. I do have some additional restrictions... IE this must be a recapture, ie To(move) must be identical to To(opponent's last move) which would make it a recapture. You don't want to say easy move too quickly. There is a famous position from Cray Blitz vs Belle in 1981, where white could play Qxb6 (the knight appeared to be hanging, but taking it led to great difficulty). Cray Blitz thought it was "easy" and didn't search long enough to see it was poisoned...
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