Chess engine: Greko 2021.05

Greko - UCI chess engine, Author: Vladimir Medvedev 
Rating JCER=2648

GreKo 2021.05 (15-May-2021):

Numerous changes in search and evaluation.

Main differences with 2020.03:

- Refactored and simplified code for search. Use the same function for all node types.

- More parameters for evaluation weights. Use tabulated values instead of quadratic approximations.

- Optimization in hash key calculation. Pawn hash key now is a part of main hash key.

- Use simpler time management algorithm.

- Use stochastic gradient descent as a single training method, instead of mix with coordinate descent before.

- Trained from pure material weights in 1.6 M positions from self-play games, fixed depth = 5.

Estimated playing strength is +20...+50 Elo points over 2020.03, depending on time settings.

The slower time control the stronger.

Greko 2021.05 - download