Koivisto

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Koivisto, an UCI compliant open source chess engine by Kim Kåhre and Finn Eggers, at times supported by Eugenio Bruno, written in C++, and first released on GitHub in September 2020 under the GPL v3.0. The bitboard engine provides automated evaluation tuning by logistic regression, either using stochastic gradient descent or AdaGrad. Koivisto 5.0 in July 2021 replaced the perceptron approach of a real-men-evaluation (RME) by an own NNUE, as of Koivisto 5.9, with two layers. =Features=

Board Representation

 * Bitboards
 * Magic Bitboards

Search

 * Lazy SMP (2.0)
 * Iterative Deepening
 * Aspiration Windows (3.0)
 * Principal Variation Search
 * Transposition Table
 * Move Ordering
 * Counter Moves History
 * History Heuristic
 * Internal Iterative Deepening
 * Killer Heuristic
 * MVV/LVA
 * SEE
 * Selectivity
 * Extensions
 * Check Extensions if SEE >= 0
 * Singular Extensions
 * Reductions
 * Late Move Reductions
 * Razoring
 * Pruning
 * Futility Pruning
 * Null Move Pruning
 * Mate Distance Pruning
 * Late Move Pruning
 * SEE Pruning
 * Quiescence Search

Evaluation

 * NNUE (5.0)
 * Tapered Eval
 * Piece-Square Tables of floats
 * Mobility
 * Bad Bishop
 * Rooks on (Semi) Open Files
 * Tactical Patterns
 * Hanging Pieces
 * Pinned Pieces
 * Evaluation Patterns
 * Outposts
 * Fianchetto
 * Pawn Structure
 * Doubled Pawn
 * Isolated Pawn
 * Passed Pawn
 * Blockade of Stop (3.0)
 * Backward Pawns
 * Open Pawns
 * King Safety
 * Attacking King Zone
 * King Tropism
 * Castling Rights (3.0)
 * Tempo (3.0)
 * Draw Evaluation (3.0)
 * Float SSE Dot products
 * Automated Tuning by Logistic Regression

Misc

 * Syzygy Bases via Fathom

=Forum Posts=
 * Re: New engine releases 2020 by Finn Eggers, CCC, September 02, 2020
 * Re: New engine releases 2020 by Finn Eggers, CCC, September 03, 2020


 * Koivisto by Gerd Isenberg, CCC, September 04, 2020
 * Re: Koivisto by Finn Eggers, CCC, September 04, 2020


 * Koivisto 2.0 by Finn Eggers, CCC, September 08, 2020
 * Koivisto 3.0 (Including binaries) by Kim Kåhre, CCC, October 17, 2020
 * Koivisto v4.0 release by Eugenio Bruno, CCC, November 09, 2020
 * Koivisto 5.0 by Finn Eggers, CCC, July 07, 2021
 * Koivisto 6.0 by Finn Eggers, CCC, July 21, 2021
 * Koivisto 7.0 by Finn Eggers, CCC, October 31, 2021

=External Links=

Chess Engine

 * GitHub - Luecx/Koivisto: UCI Chess engine
 * Evaluation · Luecx/Koivisto Wiki · GitHub
 * Regression tests · Luecx/Koivisto Wiki · GitHub
 * Koivisto Chess
 * Koivisto in CCRL 40/15

Misc

 * Koivisto - Wiktionary
 * koivikko - Wiktionary


 * Koivisto from Wikipedia
 * Koivisto (surname) from Wikipedia

=References= Up one Level