Author: David Rasmussen
Date: 07:57:47 01/23/02
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On January 22, 2002 at 10:39:07, Robert Hyatt wrote: >> >>You are right. I don't take care of that now. Can you tell me where in Crafty >>this is done? As far as I could see, if you fail high at the root, whether in a >>null-window search or not, you just return. So maybe some code in iterate.c >>takes care of this? I couldn't find it though. I couldn't find anything that >>discriminates between null-windows fail-highs and alpha;beta windows fail-highs. > > > >You have to look carefully. In the SearchRoot() code, I call search >on the first move with a normal window (alpha/beta passed in from outside >SearchRoot()). On the remaining moves, I call search with the usual alpha, >alpha+1 PVS window. If I fail high here, _nothing_ is done except to re-search >with alpha,beta. If it doesn't fail high here, nothing is updated and the >original best move and PV is still there. If I fail high here, then I do update >the best move and PV and drop back to Iterate() to adjust beta and try again... > Mmm. I got confused. I believe now that I do the same thing as you. There is something unclear herem though: When you say that you don't trust a fail high from the null-windows search, I thought you meant that you didn't trust it if the score was above beta. But as far as I can see you do. And I do too. What you don't trust is a fail high from the null-windows search if the score is above or equal to alpha+1. In that particular search, a score of alpha+1 or higher is of course a fail-high, but now a fail-high compared to the aspiration beta value of the root. So my question now is: How come we can trust a fail high from null-window searches, if the score returned is > beta? /David
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