Stefan Pohl Computer Chess

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Patricia - the EAS ChessEngine

The strongest super-aggressive engine ever created

"Patricia is brilliant" - Ed Schroeder (Computerchess legend, author of Rebel engine and famous chesscomputers (Mephisto MM IV, Polgar, Milano, Risc and many more!))

"I am checking games with Patricia engine. It's totally crazy! I haven't seen any engine play like this" - GM Vidit Gujrathi (world ranking #26, Indian Chess Olympiad gold medalist in 2024), 2025/07/27 on Lc0-discord

See a Youtube-video with 3 games played by Patricia here

Patricia by Adam Kulju is the first engine besides Ed Schroeder's Rebel EAS, using my EAS-Tool (= Engine Aggressiveness Statistics Tool) to make the engine playing more aggressive:

It's worth noting that Patricia is still well into superhuman territory, with an estimated CCRL elo of 3500; she can put up a solid fight against top engines, and can crush any human or weak engine that dares to oppose her.

If you think Patricia is a cool project, please spread the word of it! There are lots of people interested in an aggressive engine, whether it be for sparring or for other purposes, and greater awareness of what should be the undisputed queen of style would make their wish come true.

Since the 1950s, the only goal of computerchess was gaining Elo. But in these days of superstrong engines beyond 3700+ Elo, IMHO it makes a lot of sense, to make engines playing more spectacular, aggressive and interesting, instead of just gaining more and more Elo... Since my EAS-Tool was made, it is possible for the first time, to measure the aggressiveness of engines. And so, using the EAS-Tool, to make an engine playing more aggressive, is the next logical step of development in computerchess.

2026/08/31 Patricia 5.0 xtremeEAS (this experimental version uses the super-aggressive net all the time, which is normally used only for playing vs. humans, when using skill-level below 21). Download here (this is a non-officlal experimental version, so avx2 Windows binary, only)

In my testrun, Patricia 5.0 xtremeEAS played -70 Celo weaker than Patricia 5, but still +14 Celo stronger than Patricia 4. But the EAS-score increased from 556k (Patricia 4) and 644k (Patricia 5) to 751k (= +35.1% to Patricia 4 and +16.6% to Patricia 5). IMHO, this is a very good deal, compared to Patricia 5 default...

Download 794 spectacular sac-wins of Patricia 5 xtremeEAS played in my testrun here

Download the latest Patricia 5.1 from Patricia GitHub

Download the regular Patricia 5 including source and binaries for Windows, Linux, Android here

My small Gambit Opening-book (using J.Noomens Gambit-files) for Patricia is here

Download ArenaGUI with Patricia 5 installed and ready for play here

The author of Patricia (Adam Kulju) wrote this:

"Patricia is, per the EAS tool, unquestionably the most aggressive superhuman chess engine ever created (and the most aggressive engine of any kind that I currently know of).

The metric that Patricia's aggression claims are based off of is Stefan Pohl's EAS-Tool, which is the most well known and well regarded tool for determining the aggressiveness of chess engines. It looks at a combination of factors, such as sacrifice rate, short win rate, and unnecessary draw rate, and outputs a score that captures how "exciting" an engine tends to play.
A huge shoutout to Stefan Pohl. His EAS Tool works wonderfully, makes properly and objectively testing for increase aggression possible, and is the measure by which Patricia development progressed. He was also very invested in Patricia's development and explained many features of the EAS tool to me so that I had a better understanding of what was a sacrifice and what wasn't. He has put a lot of time into quantifying style, and I am happy to have Patricia be a proof-of concept and culmination of his ideas."

I did testruns of Patricia vs. 14 weaker engines of my full UHO ratinglist. Mention, weaker engines means here 3500+ Celo, so these engine are way too strong for Patricia. You can see the result in the Full UHO Ratinglist

Here the bottom of the Full UHO Ratinglist:

183 Patricia 5.1 avx2 : 3509 5 5 14000 48.5% 3520 51.1% (NEW) 184 Alexandria 5.1.0 avx2 : 3506 4 4 14000 35.7% 3616 46.1% 185 Seer 2.6.0 avx2 : 3497 3 3 41000 47.1% 3520 42.1% 186 Arasan 24.2.1 avx2 : 3487 4 4 15000 29.2% 3649 43.5% 187 Stockfish 16 HCE a512 : 3482 4 4 14000 44.6% 3520 42.1% 188 Alexandria 5.0.0 avx2 : 3480 3 3 31000 48.9% 3488 41.5% 189 Stockfish BAE 1.0 : 3478 4 4 14000 44.2% 3520 48.6% 190 Viridithas 11.0.0 avx2 : 3477 3 3 33000 47.9% 3494 41.9% 191 Velvet 7.0.0 avx2 : 3475 5 5 16000 30.7% 3624 43.1% 192 Stockfish final HCE : 3470 4 4 31000 47.4% 3490 37.9% 193 Patricia 5.0 avx512 : 3465 5 5 14000 42.4% 3520 44.9% (OLD) 194 Cerberus 2722145081r9b : 3464 4 4 14000 42.2% 3520 43.5% 195 Slow Chess 2.9 avx2 : 3451 4 4 31000 45.5% 3486 41.8% 196 Cerberus 21124081r81 : 3447 5 5 14000 39.9% 3520 37.4% 197 Rebel Extreme avx2 : 3402 5 5 14000 34.0% 3520 39.3% 198 Patricia 5 xtremeEAS : 3395 4 4 14000 33.1% 3520 37.3% 199 Patricia 4.0 avx2 : 3381 5 5 14000 31.4% 3520 32.2% 200 Revenge 1.0 avx2 : 3356 5 5 15000 18.3% 3628 30.3% 201 Jackal 2.0.0 avx512 : 3348 5 5 14000 27.5% 3520 30.5% 202 CSTal 2.1 EAS : 3343 5 5 14000 26.9% 3520 29.6% 203 Rodent V Tal : 3331 5 5 14000 25.6% 3520 29.5% 204 Rebel Extreme 1.1 : 3316 5 5 14000 24.0% 3520 25.4% 205 CS Tal Extreme : 3265 5 5 14000 19.2% 3520 20.5% 206 Patricia 3.1 avx2 : 3209 6 6 14000 14.7% 3520 21.1%

And now, see the top of the EAS full Ratinglist (calculated out of the games played for the Full UHO Ratinglist):

early bad avg.win Rank EAS-Score sacs sacs shorts draws moves Engine/player --------------------------------------------------------------------------- 1 818536 55.32% 43.85% 53.48% 06.26% 63 CS Tal Extreme 2 750655 57.26% 45.49% 44.36% 05.00% 66 Patricia 5 xtremeEAS 3 748559 52.40% 42.58% 49.75% 08.28% 65 Rebel Extreme 1.1 4 712625 51.61% 43.75% 41.43% 05.49% 66 Patricia 3.1 avx2 5 653831 50.65% 39.79% 41.13% 07.20% 68 CSTal 2.1 EAS 6 643722 50.79% 41.53% 42.61% 05.85% 67 Patricia 5.0 avx512 7 638648 52.20% 47.83% 39.07% 05.85% 67 Cerberus 2722145081r9b 8 619647 54.68% 34.28% 41.62% 05.65% 67 Patricia 5.1 avx2 9 598682 47.69% 37.02% 42.62% 07.04% 66 Rodent V Tal 10 555597 46.96% 40.00% 34.95% 03.46% 70 Patricia 4.0 avx2 11 526843 43.56% 41.14% 33.89% 04.21% 68 Cerberus 21124081r81 12 487400 35.98% 35.25% 35.51% 07.05% 70 Rebel 3.0 EAS 13 428179 37.88% 38.53% 28.30% 08.79% 75 Rebel Extreme avx2

Here 20 impressive wins of Patricia 5.0 xtremeEAS in this testrun in the pgn-viewer (engines started thinking at move 7).

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