Author: Ed Schröder
Date: 01:57:00 01/08/03
Go up one level in this thread
On January 08, 2003 at 04:31:23, Uri Blass wrote: >On January 07, 2003 at 16:52:14, Ed Schröder wrote: > >>On January 07, 2003 at 16:05:06, Tord Romstad wrote: >> >>>On January 07, 2003 at 07:17:27, Ed Schröder wrote: >>>> >>>>Let's go through a couple of xray examples: >>>> >>>>[d]rn1qkbnr/pbppp1pp/1p3p2/8/2B5/1QP1P3/PP1P1PPP/RNB1K1NR b KQkq - >>>> >>>>The knight on G8 is hanging, 2 attackers, one defender, the lowest attacking >>>>piece is a bishop. You can extract this from the bit settings. >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>>[d]r2qkbnr/pbppp1pp/1pn2p2/3Q4/2B5/2P1P3/PP1P1PPP/RNB1K1NR b KQkq - >>>> >>>>The knight on G8 is not hanging because the lowest attacking piece is a Queen. >>> >>>I still don't quite understand this, I'm afraid. How do you determine the >>>lowest attacking piece from your bit settings in the presence of an x-ray >>>attack? How do WB[G8] look for the above two positions? The way I understand >>>the section about Rebel's eval on your homepage, the bit vector would look like >>>this in both cases: >>> >>>+------+------+------+------+------+------+------+------+ >>>| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | >>>+------+------+------+------+------+------+------+------+ >>>| Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | >>>| ATTACKERS | |BISHOP| | | | >>>+------+------+------+------+------+------+------+------+ >>>| 0 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | >>>+------+------+------+------+------+------+------+------+ >>> >>>Clearly I am misunderstanding something, but I am not sure what ... >>> >>>Tord >> >> >>I had to look at the code to understand myself, it's stuff from 16-18 years >>back. >> >>We are scanning Bc4: >> >>Bc4 -> Qd5 -> e6 -> f7 -> Ng8 >> >>The squares AFTER d5 (e6, f7 and g8) the bits are not set, only a WB[sqaure]++; >>is done, so the square G8 will look as follows: >> >>>+------+------+------+------+------+------+------+------+ >>>| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | >>>+------+------+------+------+------+------+------+------+ >>>| Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | >>>| ATTACKERS | |BISHOP| | | | >>>+------+------+------+------+------+------+------+------+ >>>| 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | >>>+------+------+------+------+------+------+------+------+ >> ^^^^^^^^ >> >>Hope this helps :) >> >>Ed > >take the following position > >[D]4n1k1/8/5b2/8/5R2/5R2/8/6K1 w - - 0 1 > >I guess that you have the following bits for white about f6 > > >+------+------+------+------+------+------+------+------+ >| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | >+------+------+------+------+------+------+------+------+ >| Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | >| ATTACKERS | |BISHOP| | | | >+------+------+------+------+------+------+------+------+ >| 0 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | >+------+------+------+------+------+------+------+------+ > >the following bits are for black > >+------+------+------+------+------+------+------+------+ >| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | >+------+------+------+------+------+------+------+------+ >| Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | >| ATTACKERS | |BISHOP| | | | >+------+------+------+------+------+------+------+------+ >| 0 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | >+------+------+------+------+------+------+------+------+ > >I guess that in this case your table tell you that the bishop at f6 is hanging >but the value of hang is only 1 because if you have rook and 2 attackers and >knight bishop as single defender it means that knight is hanging by 1 pawn. > >Am I correct? Yes, you have understood well. Bf6 is hanging, TABLE will return 1 (expected gain is one pawn). >Note that The main problem that I find when I think about it is not wrong >detection of hanging pieces when there are 2 defenders and 3 attackers but wrong >detection when there are pins(not to the king assuming that you have a legal >move generator) or other threats. > >Consider the following position >[D]rn1qkbnr/ppp2ppp/8/3pp3/4P1b1/3P1N2/PPP2PPP/RNBQKB1R w KQkq - 0 1 > >I guess that Rebel will detext the pawn at e5 as hanged. Yep, to make the extra code to detect cases like this is not productive, better have a wrong move-ordering so now and then. It just doesn't hurt. >consider the following position > >[D]5bk1/8/8/2R5/8/R7/8/6K1 w - - 0 1 > >The a3 rook is also under indirect threat so it may be better to consider it for >better order of moves Rebel recognizes such patterns in EVAL, it usually is rewarded with a bonus of 1 pawn, it isn't used for move-ordering. Ed >Uri
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