Author: Heiner Marxen
Date: 13:06:52 06/29/00
Go up one level in this thread
On June 29, 2000 at 14:03:32, Robert Hyatt wrote: >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 | | | | | Hey, thanks very much for these numbers, Andreas! I had plans to do such an analysis myself, some time. >>>>>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. Yes, I do the same in Chest (I check for pseudo legality, not true legality, i.e. I just check whether an opposing pawn is in the right place). It may be noteworthy, that FEN and EPD require to indicate an e.p. target for every double step of a pawn, regardless of opposing pawns being in an appropriate position. I consider that a bug in FEN/EPD. Heiner
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