Author: Robert Hyatt
Date: 11:03:32 06/29/00
Go up one level in this thread
On June 29, 2000 at 11:17:20, blass uri wrote: >On June 29, 2000 at 10:54:38, Andreas Stabel wrote: > >>On June 29, 2000 at 09:11:47, Robert Hyatt wrote: >> >>>On June 29, 2000 at 08:16:25, Andreas Stabel wrote: >>> >>>>I have made a program that calculates this and here is the result to ply 7. >>>> >>>> | | Unique nodes | Unique nodes | Unique nodes | Factor | >>>>Ply| Total # nodes | ep = pawn two | ep = opposite| ep = Only if | prev. | >>>> | | | pawn can hit | ep is legal | row | >>>>---+---------------+---------------+--------------+---------------+--------| >>>> 0 | 1 | 1 | 1 | 1 | | >>>> 1 | 21 | 21 | 21 | 21 | 21.00 | >>>> 2 | 421 | 421 | 421 | 421 | 20.05 | >>>> 3 | 9323 | 8023 | 5783 | 5783 | 13.74 | >>>> 4 | 206604 | 109262 | 77796 | 77796 | 13.45 | >>>> 5 | 5072213 | 1351950 | 898812 | 898812 | 11.55 | >>>> 6 | 124132537 | 15334851 | 10281864 | 10281862 | 11.44 | >>>> 7 | 3320034397 | 160373323 | 106193912 | 106193643 | 10.33 | >>>> 8 | 88319013353 | | | | | >>>> 9 | 2527849247520 | | | | | >>>> >>>>It is interesting to note how great the reduction is just by not >>>>setting the E.P. target square if there is not pawn to hit. This simple >>>>test reduses the number of unique positions by a third ! >>> >>> >>>How is this happening? If no ep is possible, how can you get more nodes when >>>you set the ep target, even though no pawn can make the capture??? >>> >> >>Two positions will be different with and without the E.P. target square set >>because they will get different hash signatures. So if a chess program first >>searches one and then later in the search encounter the other it will have >>to search again because it will not realize that it is in fact functionally >>the same position. If you just chech each time a pawn is move two forward, if >>there exist a pawn of the oposite colour which may hit this pawn before you >>set the E.P. target square you will avoid this. > >I understand that you say that chess programs have different hash signature for >the position after 1.Nf3 Nf6 2.d4 and the position after 1.d4 Nf6 2.Nf3 because >they assume in the first position that the d4 may be captured next move. > >I believe that it is correct only for part of the chess programs. >I guess that the time that programs waste is bigger than the time that they save >by calculating the hash signature faster but I have no experience with it so I >may be wrong. > >It is not surprising that there are many positions when pawns get forward 2 >squares and inspite of that they cannot be captured by the en passent rule and >it is not surprising that the starting position has many cases like this case >because there are many pawns that can move 2 squares. > >Uri All I can say is that I do this correctly internally. I only set the ep flag if a pawn moves two squares _and_ it can actually be captured by an opposing pawn.
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