Author: Alessandro Scotti
Date: 12:34:52 02/27/06
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Hi H.G., thanks for this explanation, it's a very interesting and new approach for me... will try to see if it works for me too, although it seems it will take a bit of work. On February 27, 2006 at 12:23:31, h.g.muller wrote: >In my program from the mid-eighties, which had to go by without hash tables >because those day's memory sizes did not allow them, I evaluated such positions >dynamically (through search) in QS. The rule was that in a Pawns ending you were >not allowed to break off the search after a Pawn move. I considered this >situation logically equivalent to a recapture, and awarded the fact that the >opponent had a Pawn that could apparently move in the evaluation as if the Pawn >already was a Queen. (The "guilty-unless-proven-innocent principle".) >Furthermore, QS always considered Pawn moves of a Pawn that moved on ply n-2, >just as normally you continue to consider recaptures to the same square. Just >like recaptures eventually must run out, such Pawn moves do as well, because >either the pawn bumps into something that blocks it, is captured (QS always >considered capturing the piece that last moved), or promotes. > >Of course in the face of the queening threat that was expressed in the static >evaluation, the opponent would have to be given some moves to prove the >innocence. So I allowed only King moves that reduced the distance between King >and the square in front of the Pawn. (I could have allowed only the one move >that reduced this distance most, to completely avoid branching is such a QS >'tree' unless captures/recaptures became possible. But in practice the number of >paths a King could take to 'fetch' the Pawn, if that was possible at all, never >exploded much.) Without anything in the way this counted out automatically the >quadrant rule. > >In situations like the diagram above the line 1. b6, a7xb6 (recap) 2. a6xb6 >(recap), Kxx (hunt) 3. b7 (race), Kxx (hunt) 4. b8Q as well as 1. b6, Kxx (hunt) >2. b6xa7 (race, cont. capt.), Kxx (hunt) 3. a8Q would be fully covered in QS. >Except perhaps the first move (depending on what went on previously), so that a >one-ply search would see the promotion. > >This gave a much more stable search, because lines of play for which the current >eval was unclear, and that could end up either a Queen up or a Pawn down >(depending on subtleties as in the diagram), were first resolved in a deep but >narrow search before alternatives were considered. For such promotion races >iterative deepening proved pointless, that would be similar to controlling tree >size by first adding slider moves that do one step along each ray, and in the >second iteration add the two-step moves, etcetera. As long as you don't know if >there is an undefended Queen or a defended Pawn at the end of the ray, you have >no idea where the score is going, and it is useless to compare it to other moves >that are resolved.
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