Hivemind — Bughouse TwinBoard-S, clock lineage

Networks for Hivemind, a UCI engine for Bughouse chess, trained to play on real clocks.

The TwinBoard-S networks learned bughouse with a single time-advantage bit: one team may sit (wait instead of moving) for the whole game. This lineage continues from the last of them and learns from self-play on a simulated clock instead, where a team may sit only while it actually leads, and every action it takes while on turn on both boards costs it its own move time.

Files

Clock inputs

Same TwinBoardNet (twin-s, no attention) as the TwinBoard-S networks, reading 39 planes per board (78 in all): the 37 planes of input representation version 3, plus two clock planes that both boards carry with the same values, from the point of view of the team to move:

Iteration 0 reads only the 37 version-3 planes; the engine drops the clock planes for it. Training widens its first layer with zero weights for the two new planes, so iteration 1 starts out computing exactly what iteration 0 does.

Search with the clock model so the network gets real clock inputs:

setoption name TimeModel value clock
setoption name TimeLeadMs value 4200        # our lead over the diagonal opponents
setoption name TeamMoveTimeMs value 2300     # what one of our actions costs our clock
setoption name OpponentMoveTimeMs value 1500

Do not use iteration 0, or any earlier TwinBoard-S network, with TimeModel clock: they read the lead as a permanent right to sit, and their evaluation jumps by about 26 pawns as the lead crosses zero.

Results

Through iteration 11 an iteration was promoted only if it scored at least 50 % against the network that played its self-play; from iteration 12 it is promoted unless the upper end of its 95 % Elo CI against that network is below 0. The chart covers iterations 1–10. Every iteration but 9 has won its promotion match (bottom panel); iteration 9 drew level with iteration 8 (493–498–9) and was not promoted, so iteration 10 played the same generator and was matched against iteration 8. Adding up the promoted iterations' wins (dashed line) puts iteration 10 about 290 Elo above iteration 0. Played head-to-head against iteration 0 (solid line), iterations 2–7 all land between +155 and +200 Elo. Each step's gain over the network before it holds up in its own match, but most of it does not show up against iteration 0, which searches on the binary time advantage it was trained on rather than the clock. Read the head-to-head line as the conservative measure. The match against iteration 0 stopped after iteration 7; from iteration 11 every iteration is matched against iteration 10 instead (twin-s-clock-anchor-it10.onnx in the training setup), a baseline that reads the clock.

Each iteration's self-play is played by the latest promoted network at about 800 nodes per move on a simulated clock. Training starts from the previous iteration's checkpoint and takes 1.5 passes over the new positions and 0.5 over a replay window of the previous ones (the previous 3 iterations through iteration 7, 6 from iteration 8). The local training state was lost after iteration 10, so iteration 11 started from the published iteration 10 checkpoint with no replay, and the window is refilling from iteration 11 onwards. From partway through iteration 10, self-play keeps each team's search tree between its moves (tree reuse), which carries over about 13 % of each search's visits; the training targets are still the root visit counts of 800-node searches.

Matches are 1,000 games at 100 ms per move unless noted, played in colour-swapped pairs that share the opening, the starting lead and both teams' simulated move times (0.1–3 s per action). Both sides of a match always use the same engine build. Iteration 0 searches on the binary time advantage taken from the real clock, since it cannot read the clock planes. Scores are wins–losses–draws for the newer network; CIs are 95 %. Iteration 1 won about 70 % whether it started ahead, behind or level on the clock.

Policy strength without search

To see how much each iteration improved the network itself, separately from search, every iteration played 3,000 games against iteration 10 with its raw policy: one node per move (the root's network evaluation only, no tree search), on the same simulated clock and openings.

The policy improves at almost every step, but much less than the search results above: about 80 Elo from iteration 1 to 13 against about 290 summed over the promotion matches. Gains shrink as training goes on (about 60 Elo from 1 to 7, about 22 from 7 to 13). Iterations 11–13 all have stronger policies than iteration 10 even where search hides it: iteration 11 lost to iteration 10 with search (−18) but is +9 on policy alone.