Author: blass uri
Date: 08:17:20 06/29/00
Go up one level in this thread
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
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