Stefan Pohl Computer Chess

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Patricia - the EAS ChessEngine

The most aggressive superhuman 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

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.

2025/10/01 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 ArenaGUI with Patricia 5 xtremeEAS installed and ready for instant play here

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

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 a testrun of Patricia 5.0 xtremeEAS 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:

Program Celo + - Games Score Av.Op. Draws

143 Stockfish final HCE : 3470 3 3 28000 46.2% 3499 38.4% 144 Patricia 5.0 avx512 : 3466 4 4 14000 42.4% 3520 44.9% 145 Slow Chess 2.9 avx2 : 3450 3 3 28000 44.2% 3495 42.7% 146 Cerberus 21124081r81 : 3447 4 4 14000 39.9% 3520 37.4% 147 Patricia 250510 a512 : 3441 4 4 14000 39.0% 3520 43.0% 148 Rebel Extreme avx2 : 3403 4 4 14000 34.0% 3520 39.3% 149 Patricia 5 xtremeEAS : 3396 4 4 14000 33.1% 3520 37.3% (NEW) 150 Patricia 4.0 avx2 : 3382 5 5 14000 31.4% 3520 32.2% 151 Revenge 1.0 avx2 : 3356 5 5 15000 18.3% 3628 30.3% 152 CSTal 2.1 EAS : 3343 5 5 14000 26.9% 3520 29.6% 153 Monty 241220 a512 : 3321 5 5 14000 24.6% 3520 35.4% 154 Rebel Extreme 1.1 : 3316 5 5 14000 24.0% 3520 25.4% 155 Patricia 3.1 avx2 : 3210 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 750655 57.26% 45.49% 44.36% 05.00% 66 Patricia 5 xtremeEAS (NEW) 2 748559 52.40% 42.58% 49.75% 08.28% 65 Rebel Extreme 1.1 3 712625 51.61% 43.75% 41.43% 05.49% 66 Patricia 3.1 avx2 4 660963 50.51% 44.01% 41.89% 06.08% 67 Patricia 250510 a512 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 595083 48.39% 44.08% 38.12% 05.82% 67 Cerberus 21125081r9b 8 555597 46.96% 40.00% 34.95% 03.46% 70 Patricia 4.0 avx2 9 526843 43.56% 41.14% 33.89% 04.21% 68 Cerberus 21124081r81 10 428179 37.88% 38.53% 28.30% 08.79% 75 Rebel Extreme avx2 11 381300 32.46% 39.90% 28.36% 09.25% 71 Velvet 8.1.0 risky 12 373824 34.75% 43.68% 28.42% 10.27% 73 Velvet 8.0.0 risky 13 366894 31.18% 35.86% 33.98% 17.09% 71 Revenge 1.0 avx2

Patricia 5 xtremeEAS is the new #1 and the most aggressive playing engine on the planet. Awesome!

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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