Author: Laurens Winkelhagen
Date: 09:24:28 11/22/04
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On November 22, 2004 at 11:20:19, Steve Coladonato wrote: >On November 22, 2004 at 09:16:58, Laurens Winkelhagen wrote: > >> >> >>Hi Steve, >> >>I'm not sure if I understand you correctly, so I don't know if this reply will >>make sense to you, but: >>tablebases only tell only one side of the story: there is a KRPKBP tablebase but >>there won't be a KBPKRP tablebase. The board is flipped appropriately. There are >>obviously positions where KBP will win over KRP, which is why there are both >>maxDTM for 1-0 and for 0-1. There wouln't need to be 0-1 maxDTM scores when >>there would be a seperate KBPKRP tablebase, but there isn't;-) >> >>Hope I make sense, Laurens. > > >Thanks Laurens. > >It's not totally clear yet. I will have to think over the concept of flipping >the board to figure out why tablebases provide the statistics for either side >winning. > >In the example I gave, white had the rook and black had the bishop. Hence, I >don't think there is a need for flipping the board and the tablebases should >determine whether white wins, loses, or draws. Is that correct? > >Thanks. > >Steve Indeed. But I feel I have obfuscated the issue: One possible source of confusion occured to me while I was browsing through some EGTB-probe code: When I said flipping the board, I actually meant inverting the color of the pieces. Let's use some of the Crafty Code Comments to clarify things: /* ************************************************************ * * * yes, finish setting up to probe the tablebase. if * * black is the "winning" side (more pieces) then we need * * to "invert" the pieces in the lists. * * * ************************************************************ */ In your example, white is the "winning" side, hence the board need not be flipped. Now, the next step is clear: /* ************************************************************ * * * now check to see if this particular tablebase for this * * color to move is registered. * * * ************************************************************ */ Probing the tablebases will now give one of three possible types of outcome: 0 = it's a draw positive = I (site-to-move) am gonna win in xxx half-moves negative = I'm gonna lose in xxx half-moves Actually, I didn't even see your first post until now. So, in actuality there are two KRPKBP tablebases, one for wtm and one for btm. Both give both 1-0 and 0-1 results. This is why we can distinguish four maxDTM values. Inverting the pieces is only relevant in case black has KRP and white KBP. Regarding 1/2-1/2 results: "maxDTM" for 1/2-1/2 is by definition pointless, which is why the EGTB's return the value "0" for such positions. I Hope this clarifies things, Laurens, author of Jan Willem (with a big help from kind Prof. Hyatt regarding the EGTB-probe code, thanx again, Robbert Hyatt:-)
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