Chess engine: Stockfish 19111809

Stockfish - UCI chess engine, interesting compiled by Joost VandeVondele

Use exploration rate for reductions 

This patch measures how frequently search is exploring new configurations. This is done be computing a running average of ttHit. The ttHitAverage rate is somewhat low (e.g. 30% for startpos) in the normal case, while it can be very high if no progress is made (e.g. 90% for the fortress I used for testing). 

This information can be used to influence search. In this patch, by adjusting reductions if the rate > 50%. A first version (using a low ttHitAverageResolution and this 50% threshold) passed testing: 

STC 
LLR: 2.96 (-2.94,2.94) [-1.50,4.50] 
Total: 26425 W: 5837 L: 5650 D: 14938 Elo +2.46

LTC 
LLR: 2.96 (-2.94,2.94) [0.00,3.50] 
Total: 32313 W: 5392 L: 5128 D: 21793 Elo +2.84

However, as discussed in pull request 2414, using a larger ttHitAverageResolution gives a better approximation of the underlying distributions. This needs a slight adjustment for the threshold as the new distributions are shifted a bit compared to the older ones, and this threshold seemingly is sensitive (we used 0.53125 here). 

This final version also passed testing, and is used for the patch: 

STC 
LLR: 2.95 (-2.94,2.94) [-1.50,4.50] 
Total: 16025 W: 3555 L: 3399 D: 9071 Elo +3.38

LTC 
LLR: 2.96 (-2.94,2.94) [0.00,3.50] 
Total: 37576 W: 6277 L: 5998 D: 25301 Elo +2.58



Rating JCER=3257

Stockfish 19111809 - download