Chess engine: Eubos 2.12

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June 11, 2022

Chess engine: Eubos 2.12

Eubos - a basic Java chess engine, written for kicks. Uses jcpi for the UCI protocol parts. Kind of weak, doesn't evaluate for king safety, for example. Now uses transpostion hashing, but because it runs in the Java VM on a bog standard PC, doesn't search very deeply (around 100K Nodes/s, though this is actually quite hard to evaluate due to the hashing).

Author: Chris Bolt Rating CEDR=1788

v.2.12

Features

Added simplified evaluation of candidate passed pawns to the pawn evaluation

Add bespoke evaluation for KPK endgames (disabled in the release as it is over-simplified)

Added standard algorithm (from Chess Programming Wiki) for computing the manhattan distance between squares (with intention of using it in KPK endgames for square of pawn evaluation

Added King Tropism aspects to the bespoke Eubos king safety algorithm using the manhattan distance for Queens and Knights

Added capability to send just a single best move at a position, rather than a full principal variation

Tuning / Optimisation / Tweaks

Create a different set of piece material values for the Endgame material evaluation

Modify the piece material values to disincentivise trading minor pieces for pawns or major pieces for minor pieces plus pawns

No longer update the PV at a position if we didn't increase alpha, previously Eubos tracked the score at a position from provisional alpha, even when it was outside the current search window.

Modify move timing computation to assign fewer milliseconds to each time quanta when evaluating the current search progress. This conserves more clock, and reduces per move think time.

Optimised pawn attack aggregaton out of the per pawn evaluation - it is now just done once for the position

Modified the traditional Eubos king safety algorithm to not discount attacking bishops on the opposite square colour to our king

Optimise the check during move generation to see if a move could be illegal because the piece is pinned to the king, now it only considers diagonal/ranke and file attacking sliders if they are present in the position

Search at least 6 quiet moves before doing LMR

Increase default LMR to depth/3

Fixes

Move timing change, if an aspiration window fails, wait for the re-search with a wider window to complete before terminating the search

No longer assign 'exact' score type when updating the Trasposition Table, as current LMR algorithm means we can't know the true depth searched (it can be reduced multiple times)

Quality

Added various EPD Test Suites as optional unit tests, derived from the Chess Programming Wiki

Fix up perft tests, which were failing due to not including under promotions in the move generation in Eubos v2.11

Refactored and simplified the Transposition static class

Use Eubos internal types in the Search Metrics class, not JCPI package types

Refactored the Test.Eubos.Main package to extract common code into a base class

Potential Improvements

Further development of KPK

Analys the frontspan of passed pawns and account for attacks/piece blocks in the evaluation thereof

To install Eubos as an engine in Arena:
1. Select Engines > Install New Engine
2. In the file browser dialog that appears, change the drop down to *.bat
3. Navigate to the Eubos binary location, select the Eubos.bat
4. Select UCI protocol to communicate with Eubos
5. That's it!

Eubos 2.12 download