Implement an old Russian proverb
"Loose pieces drop, in blitz keep everything protected"
Adding a small S(2,2) bonus for knights, bishops, rooks, and
queens that are "connected" to each other (in the sense that
they are under attack by our own pieces) apparently is a good
thing. It probably helps the pieces work together a bit better.
STC
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 12317 W: 2655 L: 2467 D: 7195
http://tests.stockfishchess.org/tests/view/5aa2d86b0ebc590297cb6474
LTC
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 35725 W: 5516 L: 5263 D: 24946
http://tests.stockfishchess.org/tests/view/5aa2fc6f0ebc590297cb64a8
How to continue from there (by Stefan Geschwentner)?
• First we should identify all other eval terms which have an overlap
with new connectivity bonus (like the outpost bonus). A simple way
would be subtract the connectivity bonus from them and look if this
better, or use a SPSA session for these terms.
• Tuning Connectivity himself with SPSA seems not so promising because
of the small range which is useful. Here manual testing changes of
Connectivity like +-1 seems better.
• The eg value is more important because in endgame the position gets
more open and so attacks on pieces are easier. Another important point
is that when defending/fortress-like positions each defending piece
needs a protection, otherwise attacks on them can break defense.
Closes https://github.com/official-stockfish/Stockfish/pull/1474
Bench: 5318575