Hi all,

about Maia and search width, I analyzed this position from round 7, Maia_1800 plays black vs Academy_1800, move 56:



Maia played 56. ... Ke4?? that immediately lost (mate in 1: 57.Rd4#).

First control: I set the position and level = 1 node, Maia_1800 plays the same: this move is indeed the "natural" one from the 1800 net knowledge.

I then increased the granted number of nodes and used multi-PV set to 4 and repeated the search (with an engine restart each time) until the Ke4 move is assigned the -M1 score, meaning Maia is fully aware of the potential blunder.

Worth reading: Lc0 options. The options that drive the search width appear to be CPuct, CPuctBase and CPuctFactor; with an additional set of options dedicated to the root of the search.

Using the default setting of lc0 (here I run the 026.3 version): CPuct & CPuctAtRoot=2.147; CPuctBase & CPuctBaseAtRoot=18368; CPuctFactor & CPuctFactorAtRoot=2.815) Maia still wants to play Ke4 up to 8 nodes searched (score -1.59).
Starting with 9 nodes searched, Maia prefers the correct move Kc4 thanks to the better score -1.52, but Ke4 is still granted -1.59. Reached depth is 3/5.

Maia needs 16 searched nodes in order to assign Ke4 the correct -M1 score; reached depth is 3/6. According to the NPSLimit I set for Maia_1800 (1.26), it requires a 12.7 seconds search (and according to the move number 56, the 30 minutes limit for all game, and the played blunder, Maia_1800 must have spent less time on that move).

Then I pushed the above UCI options to each limit in order to maximize the width of the search: CPuct & CPuctAtRoot=100; CPuctBase & CPuctBaseAtRoot=1; CPuctFactor & CPuctFactorAtRoot=1000. Maia still wants to play Ke4 up to 7 nodes searched (-1.81 score ).
Starting with 8 nodes searched, Maia prefers the correct move Kc4 thanks to the better score -1.55, but Ke4 is still granted -1.81. Reached depth is 2/4.

Now to the real gain: Maia needs only 11 searched nodes to assign Ke4 the -M1 score, depth 2/5 (reminder: default setting needed 16 nodes and depth 3/6). Associated displayed variant is Kd5e4 Rd2d4+. Maia is now aware. This result would have required 8.7 seconds search using my NPSLimit setting, a better chance than the above 12.7 using default values.

Worth additional tests over full games...
MfG,
Eric