Author: Guido
Date: 07:31:00 05/02/03
Go up one level in this thread
On May 01, 2003 at 18:11:02, Alvaro Jose Povoa Cardoso wrote: >Could you please explain what is the 'forward-pass' and the 'forward generation' >you mentioned on a previous thread? > > >Regards, >Alvaro Cardoso I try to explain the basical logic of EGTBs computation supposing to calculate the wtm (white to move) file. As said by Guy, EGTBs can be calculated in two ways: - Forward or forward-pass generation: scanning the wtm file at cycle N, for a position not yet calculated, find all the legal white moves. These are said 'forward' (= normal, usual) moves. If the execution of any_of_such_moves gives a position where black is checkmated in N-1 moves (you have to read in the btm file computed before at the N-1 cycle) then this position is a victory in N moves. Instead if execution of all_the_moves gives a position where black wins in N (or less) moves, then this position is a loss in N moves (generally you will be at cycle N+1). - Retro generation: scanning the btm_file in a position where black is checkmated in N moves, find all the legal retro (or backward) moves of the white. Legality of a retro move is obviously completely different from legality of a forward move, because you can go in a position where there is a check and pawns move backward (e.g. a6-a5). Moreover, but this doesn't interest here, promoted pieces return pawns and men can 'resurrect'. Any_position so calculated for the white is clearly a victory in N_or_less moves of the white itself to save in the wtm file. For retro generation I explain only the basic principle because the actual implementation is more complicated and needs of more than one trick. If Guy reads, answering to him in another thread, I said: "I use a bit vector only for 'lost in N' and not for 'mate in N'. Probably I use a different approach from WU-Beal.... " Now a doubt cames to me about the meaning of 'mate in N'. In my answer I intended it as 'won in N', but I'm not of english mother tongue... Ciao Guido
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.