Add doubled isolated pawn penalty.
This patch gives an additional penalty if a doubled isolated pawn is stopped
only by a single opponent pawn on the same file. Thanks to NKONSTANTAKIS,
who shared this idea on the forum!
https://groups.google.com/forum/?fromgroups=#!topic/fishcooking/vC4Qn-PMlS4.
STC:
LLR: 2.96 (-2.94,2.94) {-0.50,1.50}
Total: 84872 W: 16688 L: 16370 D: 51814
Ptnml(0-2): 1507, 9940, 19274, 10158, 1557
https://tests.stockfishchess.org/tests/view/5ec65bd955202b947dc5d4ac
LTC:
LLR: 2.93 (-2.94,2.94) {0.25,1.75}
Total: 58104 W: 7614 L: 7278 D: 43212
Ptnml(0-2): 411, 5369, 17196, 5625, 451
https://tests.stockfishchess.org/tests/view/5ec6e9f2c23f5b0710632b19
Closes https://github.com/official-stockfish/Stockfish/pull/2694
Bench: 5148950