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Commit ID d5e3e7d207538fe3ff0c86df9d9f95912f5266e9
Author Alain SAVARD
Date 2018-03-30 23:16:51 UTC
Candidate Passed Pawn Include some not fully supported levers in the (candidate) passed pawns bitboard, if otherwise unblocked. Maybe levers are usually very short lived, and some inaccuracy in the lever balance for the definition of candidate passed pawns just triggers a deeper search. Here is a example of a case where the patch has an effect on the definition of candidate passers: White c5/e5 pawns, against Black d6 pawn. Let's say we want to test if e5 is a candidate passer. The previous master looks only at files d, e and f (which is already very good) and reject e5 as a candidate. However, the lever d6 is challenged by 2 pawns, so it should not fully count. Indirectly, this patch will view such case (and a few more) to be scored as candidates. STC LLR: 2.95 (-2.94,2.94) [0.00,4.00] Total: 16492 W: 3419 L: 3198 D: 9875 LTC LLR: 2.95 (-2.94,2.94) [0.00,4.00] Total: 21156 W: 3201 L: 2990 D: 14965 This was inspired by this test of Jerry Donald Watson, except the case of zero supporting pawns against two levers is excluded, and it seems that not excluding that case is bad, while excluding is it beneficial. See the following tests on fishtest: Closes Bench: 5568461 ---- Comments by Jerry Donald Watson: > My thinking as to why this works: > > The evaluation is either called in an interior node or in the qsearch. > The calls at the end of the qsearch are the more important as they > ultimately determine the scoring of each move, whereas the internal > values are mainly used for pruning decisions with a margin. Some strong > engines don't even call the eval at all nodes. Now the whole point of > the qsearch is to find quiet positions where captures do not change the > evaluation of the position with regards to the search bounds - i.e. if > there were good captures they would be tried.* So when a candidate lever > appears in the evaluation at the end of the qsearch, the qsearch has > guaranteed that it cannot just be captured, or if it can, this does not > take the score past the search bounds. Practically this may mean that > the side with the candidate lever has the turn, or perhaps the stopping > lever pawn is pinned, or that side is forced for other reasons to make > some other move (e.g. d6 can only take one of the pawns in the example > above). > > Hence granting the full score for only one lever defender makes some > sense, at least, to me. > > IMO this is also why huge bonuses for possible captures in the evaluation > (e.g. threat on queen and our turn), etc. don't tend to work. Such things > are best left to the search to figure out.
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