No Yaku Kanchan Dama vs Break Winrates
No Yaku, No Riichi? This analysis was inspired by a recent post by Yuusei that looked at the following situation: What would you do: riichi to secure 2nd, 4s dama, or 9m breaking tenpai? Assume a "generic" reward system: [+2, +1, 0, -3] for 1st-4th place (7 dan Tenhou, Ms1 Majsoul). As discussed in Yuusei's post, due to the harsh penalty for 4th place, riichi is a bad option. The dealer is in 1st place, so the game will probably end this round. Assuming the game ends, if we just fold this hand and don't deal in to last place, we will get +1 or +0 points. We do not want last place to fight our bad wait and risk a -3pt result. So we consider the two other options. Naga cuts 4s, hoping to draw our winning tile directly or upgrade to pinfu on 6m. LuckyJ, Tencent's new Mahjong AI, cuts 9m, giving up tenpai for more pinfu upgrades, which is also what Yuusei suggests. Who is right? Simulation Set Up To answer this question, I set up a simple Markov Cha