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Always initialize and evaluate king safety
Recent tests by @xoto10, @Vizvezdenec, and myself seemed to hint that Elo could be gained by expanding the number of cases where king safety is applied. Several users (@Spliffjiffer, @Vizvezdenec) have anticipated benefits specifically in evaluation of tactics. It appears that we actually do not need to restrict the cases in which we initialize and evaluate king safety at all: initializing and evaluating it in every position appears roughly Elo-neutral at STC and possibly a substantial Elo gain at LTC. Any explanation for this scaling is, at this point, conjecture. Assuming it is not due to chance, my hypothesis is that initialization of king safety in all positions is a mild slowdown, offset by an Elo gain of evaluating king safety in all positions. At STC this produces Elo gains and losses that offset each other, while at longer time control the slowdown is much less important, leaving only the Elo gain. It probably helps SF to explore king attacks much earlier in search with high numbers of enemy pieces concentrating but not essentially attacking king ring. Thanks to @xoto10 and @Vizvezdenec for helping run my LTC! Closes official-stockfish#1906 STC: LLR: 2.95 (-2.94,2.94) [-3.00,1.00] Total: 35432 W: 7815 L: 7721 D: 19896 http://tests.stockfishchess.org/tests/view/5c24779d0ebc5902ba131b26 LTC: LLR: 2.95 (-2.94,2.94) [-3.00,1.00] Total: 12887 W: 2217 L: 2084 D: 8586 http://tests.stockfishchess.org/tests/view/5c25049a0ebc5902ba132586 Bench: 3163951 ------------------ How to continue from there? * Next step will be to tune all the king danger terms once more after that :-)
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