Author: Dan Newman
Date: 15:43:47 08/27/00
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On August 27, 2000 at 17:52:44, José Carlos wrote: >On August 27, 2000 at 17:33:15, Tom King wrote: > >>Hi all, >> >>a question for programmers on fail highs. >> >>what do you do in your program if a fail high is encountered, which on the >>research fails low? >> >>I've ignored this issue, because it doesn't seem to happen all that often (in my >>program). So if my program finds a move which fails high, even if the research >>indicates that it maybe shouldn't have failed high, it thinks the move is good. >>Maybe this is bad? At the WMCCC recently, I noticed a couple of these fail high/ >>fail low moves cropping up at critical, complex positions. Often I was unhappy >>with the move my program chose in these cases. Perhaps these fail high/ fail low >>moves need to be treated with suspicion? >> >>Cheers, >>Tom > > In Averno, when I fh, and research with a new Alfa,Beta window, if I fail low >in the research, I use Alfa as the eval of the position so, as it failed high >before, it becomes the PV move, until a better move is found. > > Hope this helps :) > > José C. In Shrike I do something rather horrible. When I fail high I open up to [alpha,+inf], and then if I fail low in the re-search, I open all the way up [-inf,+inf]. I suspect that I'm just wasting nodes in this case. In fact it seems like it often comes up with a score that's not too far from fitting into the original window... This is something I need to look at. One scheme I read about (in one of Levy's books I think) involved just continuing on when you get a fail-high, and searching all the rest of the moves--unless you get a second fail-high. Then the question becomes "which of the two fail-high moves is the best?" I don't recall exactly how you proceed after this, but you don't need to re-search any of the other moves that have already been searched that didn't fail-high. You do have to re-search the two fail-highs, however. I guess this scheme isn't very good for PVS search since you might end up without a PV to follow. -Dan.
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