Author: Robert Hyatt
Date: 19:39:23 01/18/04
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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.
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