Chess22k

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chess22k, an UCI compliant open source chess engine by Sander Maassen vd Brink, written in Java first released in January 2017. While already in the 2400 Elo range using a 64-bit Java Runtime Environment (JRE), it has not initially implemented a tapered evaluation, but abrupt transition based on piece counts per side to distinguish between middlegame and endgame terms. However, tapered evaluation was implemented in chess22k 1.5 along with new evaluation terms adjusted by Texel's tuning method. In November 2017, chess22k had its over the board tournament debut, version 1.6 played the CSVN PT 52 in Leiden, quite successful - shared 4th place with 6/9. Soon released afterwards, chess22k 1.6 requires Java 9.

=Features=

Board Representation

 * Bitboards
 * Magic Bitboards

Search

 * Lazy SMP (1.10)
 * Iterative Deepening
 * Aspiration Windows
 * Principal Variation Search
 * Transposition Table
 * Move Ordering
 * History Heuristic
 * Internal Iterative Deepening
 * Killer Heuristic
 * Selectivity
 * Null Move Pruning
 * Late Move Reductions
 * Razoring
 * Futility Pruning
 * SEE Pruning

Evaluation

 * Evaluation Hash Table
 * Tapered Eval 1.5
 * Material
 * Bishop Pair
 * Piece-Square Tables
 * Mobility
 * Trapped Pieces
 * Rooks on (Semi) Open Files
 * Outposts
 * Pawn Hash Table
 * Pawn Structure
 * Doubled Pawn
 * Isolated Pawn
 * Passed Pawn
 * King Safety
 * Pawn Shelter
 * Tactical Penalties
 * In Check
 * Hanging Pieces
 * Pinnned Pieces
 * Texel's Tuning Method

=Forum Posts=

2017

 * chess22k v1.0 by sandermvdb, OpenChess Forum, January 13, 2017
 * New release: chess22k v1.1 by Sander Maassen vd Brink, CCC, February 09, 2017
 * chess22k 1.2 released by Sander Maassen vd Brink, CCC, March 19, 2017
 * chess22k 1.3 released by Sander Maassen vd Brink, CCC, April 26, 2017
 * Texel tuning method question by Sander Maassen vd Brink, CCC, June 05, 2017 » Texel's Tuning Method
 * Impressive Texel-tuning results by Sander Maassen vd Brink, CCC, June 16, 2017
 * chess22k 1.4 released by Sander Maassen vd Brink, CCC, June 18, 2017
 * chess22k 1.5 released by Sander Maassen vd Brink, CCC, August 12, 2017
 * chess22k 1.6 released by Sander Maassen vd Brink, CCC, November 13, 2017
 * chess22k 1.7 released by Sander Maassen vd Brink, December 28, 2017

2018

 * chess22k progress overview by Sander Maassen vd Brink, January 09, 2018
 * chess22k 1.8 released by Sander Maassen vd Brink, CCC, March 04, 2018
 * chess22k 1.9 released by Sander Maassen vd Brink, CCC, April 23, 2018
 * chess22k 1.10 released by Sander Maassen vd Brink, CCC, July 09, 2018
 * chess22k 1.12 released by Sander Maassen vd Brink, CCC, December 03, 2018

2019

 * chess22k 1.13 released by Sander Maassen vd Brink, CCC, July 28, 2019

2020

 * chess22k 1.14 released by Sander Maassen vd Brink, CCC, April 26, 2020

=External Links=
 * GitHub - sandermvdb/chess22k
 * chess22k 1.4 64-bit in CCRL 40/4

=References=

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