Author: Ed Schröder
Date: 00:08:42 07/31/99
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>This is easy to test. > >My hypothesis: simple search is not good enough to discover that all moves >but one lead to mate, in any positions except for those near the point where a >game is already over (one side is mating the other). > >Ed's: A simple search is good enough to discern forcing moves. > >How about someone looking for positions where all moves but one lead to a >forced mate... IE one move must _not_ get mated, while all the rest do. >Then we decide whether the short search of Rebel can see this or not. > >Then we decide how often this kind of position occurs, and how often (when it >does) is a shallow search enough to recognize the forced nature. > >I don't think (a) it will work very well; (b) that it is worth the effort to >search with alpha=-inf, beta=+inf for every root move; (c) that by the time >this might have a chance of identifying a forcing move, the game is already >over and saving time is pointless... > >My opinion, of course... How about going one step further. Some years ago I did an experiment. Search the first iteration without A/B, then: if (best_score - second_best_score > margin_one) limit time control. if (best_score - second_best_score > margin_two) limit time control even more. etc. Also I tried this for the second iteration as well. Results were not bad at all as it also catches forced moves that aren't recaptures and escapes from checks. Moves sequences like 1..g5 2.Bg3 were also discovered and 2.Bg3 was played very fast. I also remember a case 1.a7 Ra8 preventing the pawn to promote. Since 1..Ra8 was the only move 1..Ra8 was played instantly. Note that Q-search in Rebel's first and second iteration were limited to 6 and 8 plies to prevent the search to explode when A/B is not active. I also do check extensions in Q-search to discover mates which catches the most important ones but not all of course. Ed Schroder
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