Author: Robert Hyatt
Date: 09:31:17 01/19/04
Go up one level in this thread
On January 19, 2004 at 04:57:01, William Penn wrote: >On January 18, 2004 at 23:19:26, Robert Hyatt wrote: > >>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... > >I have seen it suggested that he may prefer to leave it that way to hide his >exact search algorithm, so that others can't copy it. It might be something >special, unique, that nobody else knows about (yet). Possible? Or just verbiage? >WP Certainly a possibility. Showing the _real_ PV tends to expose part of your search strategy. Showing partial, incomplete and sometimes bogus PVs makes that harder to understand. :)
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