The NNs Depart TCEC S13

In last week's post, Battles of the Chess NNs, for this blog's current series on the Top Chess Engine Championship (TCEC), I signed off with:-

Both Leela and DeusX qualified from TCEC S13 division four to division three, another quadruple round robin with eight engines competing. As I write this, that event has reached the second stage. The engine Ethereal has a large lead over six engines (including the two NNs) which are bunched together, vying for the second qualifying place into division two.

A few days later the organizers announced, Ethereal chess engine wins the gold at TCEC Div 3:-

Ethereal, the chess engine by Andrew Grant, is the winner of TCEC Div 3. After three months of rapid development, Ethereal came stronger than ever and outwitted the competition in the division finishing 22,5/28 -- full 6,5 points ahead of competition.

Here's a copy of the final crosstable:-

What about that tie for 2nd/3rd? Both Leela (lc0) and Arasan finished with 16.0/28, Leela having the better SB. The second NN, DeusX, finished in fifth place with a minus score, 13.5. The announcement continued,

The second qualification spot was highly contested through the division. Pedone was off to a good start, but somewhere in the second half of the event it lost the advantage and was overcome by Arasan. Fixes in the cooling and power usage of the GPUs helped Leela lift off after round 20. It managed to get an impressive 5,5/6 after the GPU fix, but later could not defeat Arasan in the direct match. Arasan, with better tiebreak over Leela, climbs back to the division where it competed last season.

The TCEC rules specify,

Tiebreaks • If necessary, tiebreaks can be used to determine advancement. For all Divisions (not the Superfinal), the first tiebreak criteria is the "crash" tiebreak, meaning that if an engine has crashed once or more during the Division, it will fail qualification versus another engine that has not crashed if both of them has the same amount of points. In case of still being tied, then the direct encounter between the tied engines decides. The next criterion is the greatest number of wins, then the greatest number of wins with black. The Sonneborn-Berger is the next criteria. If they are still tied, then the tournament organizers will decide which engine gets the promotion.

I gather from this explanation that the '"crash" tiebreak' played no role. Since the minimatch between the two engines ('direct encounter') was +1-0=3 in Arasan's favor, it qualified into division two. Some Leela supporters hoped that both engines might go through, but what good are rules if they're not enforced?

For many observers, the main interest in TCEC's lower divisions was the participation of the two NNs, Leela and DeusX. Once both engines were eliminated, interest shifted to which engine will finish first for the season. Most bets are undoubtedly on Stockfish to win for the third consecutive time.