Around ten parameters allow you to modify the playing style of the Cdrill chess engine. I would like to use it to program new personalities for the engine but I'm not sure I understand how to use the "Threat" parameter. Because unfortunately the author, Ferdinand Mosca, does not provide any documentation with his engine (and gives no way to contact him!). For a long time I thought that "Threat weight" measured the engine's interest in the adversary's threats. To test this hypothesis, I created two personalities, one with a very low Threat (20) and the other with a very high Threat (350). A few games played, however, did not allow me to detect a big difference in behavior. I told myself that if Threat was a good measure of the effort spent on detecting threats, I should have a much more offensive playstyle with a low Threat and a much more defensive playstyle with a high Threat. And that Stefan Pohl's "Engine Aggressiveness Statistics" tool would allow me to confirm it. The EAS is able to measure the greater or less aggressiveness of an engine by exploring a collection of parts of this engine. So I used Arena GUI to organize a 255 blitz tournament between standard Cdrill, Cdrill with "Threat" set to 20 and Cdrill with "Threat" set to 350. Here are the results of this tournament:

Result of tournament

I then used the Engine Aggressiveness Tool to measure changes in engine behavior. However, what I see is a clear increase in aggressiveness in both cases! The aggressiveness index goes from 42408 with standard Cdrill to 114516 with low “Threat” and 143329 with high “Threat”. The most important measured parameter of EAS is the motor sacrifice taste. With 1.19%, standard Cdrill sacrifices little; this increases to 8.45% with low Threat and 9.30% with high Threat. What do you think ?

  • Threat weight is a factor to scale own piece attack on enemy pieces. For example a rook attacking enemy bishop has a normal bonus. If threat weight is 150, new_bonus = normal_bonus x 150 / 100. What is "Engine Aggressiveness Statistics". I am the author of CDrill.
    – ferdy
    Commented Apr 19 at 19:06
  • Thank you for your reply. It's a pleasure to finally read you. In summary, and if I understood correctly, a high threat favors counterattacks? Commented Apr 21 at 7:51
  • Measurement of aggressiveness by EAS: S. Pohl offers an application which carries out a statistical exploration of a batch of games in PGN format (at least 200 are needed per engine or player tested) in order to measure the aggressiveness of players . The tool collects numerous indices including the overall number of sacrifices, the number of sacrifices of pawns, the number of sacrifices of high-value pieces, the number of games ending quickly or very quickly in checkmate, the duration of the games, “bad draws” (games ending in a draw after having benefited from a material advantage), etc. Commented Apr 21 at 7:53
  • Obviously, it assigns a specific weight to the measurement of each parameter (Pohl explains this in detail in the documentation). Here is the useful link: sp-cc.de/eas-ratinglist.htm Commented Apr 21 at 7:53
  • Reading you again, Ferdy, I understand that the "Threat" parameter regulates the engine's attack. So it's not an adjustment in response to the opponent's aggressiveness. What I find astonishing is that, with "Threat" set to just 20, Cdrill's aggressiveness is still far superior to that of standard Cdrill. Commented Apr 21 at 11:17


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