Author: Ed Schröder
Date: 09:39:06 11/27/03
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On November 27, 2003 at 07:54:50, martin fierz wrote: >hi, > >i have a question about ed schröder's webpage, specifically on the hanging >pieces part. > >ed explains that he has two tables which contain attack info for each square of >the board, they look like this: > >+------+------+------+------+------+------+------+------+ >| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | >+------+------+------+------+------+------+------+------+ >| Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | >| ATTACKERS | |BISHOP| | | | >+------+------+------+------+------+------+------+------+ > >so if you have a square attacked by a white pawn and a white bishop, you get the >value 00011010 in binary notation for this square, or 26. >next, ed explains that he has a 3D table > >[piece_type][white_attack][black_attack] ([12][256][256]), which contains the >expected value for a capture on a square. > >for example, if you have a pawn which is attacked by 2 pawns and is defended by >a knight, you will find in your table that the expected material gain is 1 pawn. >up to here i understand all of this, and it seems like a great idea - you have a >SEE based on a single table lookup. it doesn't deal with xray-attacks, of >course. Rebel while creating the attack tables supports xray attacks. If you have Rebel 12 (dos or win) have a look at the file ATTACK.BIN which is the representation of the [piece_type][white_attack][black_attack] ([12][256][256] table with all its precalculated results. >but now for the real problem: let's say, you have a bishop attacked by 2 knights >and 1 rook, defended by 1 knight and 2 rooks in the first case, or defended by 2 >knights and 1 rook in the second case. >in the first case, you are winning material. in the second case not. how do ed's >tables distinguish these two cases? Check the ATTACK.BIN file :) >am i missing something here, or is this just another inaccuracy that such a >table-based SEE has (like not resolving xray attacks)? is it simply unimportant >to resolve such details? It depends how you are planning to use the information, it is great for move-ordering, q-search, static selective search, pruning, extensions, reductions, eval. However you (for example) can't replace q-search with a static evaluation of the hanging pieces, for that the data is too insecure. My best, Ed
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