Author: Robert Hyatt
Date: 20:19:26 01/18/04
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On January 18, 2004 at 23:10:55, Bob Durrett wrote: >On January 18, 2004 at 22:39:23, Robert Hyatt wrote: > >>On January 18, 2004 at 05:53:49, martin fierz wrote: >> >>>i just received my brand-new shredder 8. when using it for analysis in chessbase >>>(which is in fact the only thing i use it for), it often gives PVs which are >>>completely ridiculous - the first few moves are ok, then one side blunders a >>>piece according to the PV, but the evaluation of that line doesn't show it. >>>looks like there is a PV bug in shredder 8? is there any fix for this? i find it >>>very annoying... >>> >>>cheers >>> martin >> >> >>I have heard that Shredder (and others) try to reconstruct the PV by probing the >>hash table at the end of the search. This simply does not work with any degree >>of accuracy. IE suppose you search and reach position A while searching the PV. >> Later, at very shallow depths, you reach position A again and >>overwrite it with different "best moves" depending on the depth remaining, >>extensions triggered, etc. Now when you try to recover the PV from the hash >>table, you get the right position A, but the wrong best move. And then the PV >>looks funny. It doesn't happen every time, but if the PV is reconstructed >>enough this way, it happens often enough. I tried this _years_ ago and ran into >>the same problem. Never saw it in debugging. Saw it regularly when kibitzing >>PVs on ICC. :) >> >>I now do it the correct way, backing the PV up along with the score... >> >>Remember that this is speculation since I have never seen Shredder's source. But >>recovering the PV in this way is simply going to produce errors, and there is >>nothing that can be done about it. The first move and score will be correct, of >>course. But beyond that, who knows, and the farther out, the greater the >>probability of a bogus move. > >There was much discussion here about this problem with Shredder 7.04. You would >have thought that this would have been corrected it for version 8.0 but maybe >we'll have to wait until Shredder 8.04. : ( > >Bob D. He might not want to worry with it. It isn't a tough change, but it is a change...
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