Season 8 stage 2 full stats

Draw rate, wins

The final draw rate was 50%, the second RR had a draw rate of 39.4%, compared to the first RR that had 60.6% draws. Funny, isn't it?


Moves per game

Average = 76.3
Median = 66.75

Decisive games tend to be shorter, the second RR had shorter games than the first. Still the games of stage 1 were shorter by about 5 moves.

Time per game (hours)

Average = 4:41
Median = 4:33

Similarly the second RR games reduced the overall time per game by a few minutes, still about an hour longer per game than stage 1.

Openings

Two move book openings were used in pairs of reverse games. This means there may be a tendency of openings repeated in reverse games, but engines could choose different paths after the only two moves. Indeed, of the 132 games there were 104 distinct openings, looking at full opening names. The most repeated openings were:

Queen's Pawn: Modern : 4 times
Four Knights: Italian Variation : 3 times
Neo-Gruenfeld, 6.O-O c6 7.Nbd2 Bf5 : 3 times

Using ECO codes there were 66 different openings. The top 3 ECO codes were:
A01 6 times - Nimzovich-Larsen attack
B22 6 times - Sicillian, Alappin's variation
A36 5 times - Englsh, Symmetrical variation

Using only the first letter of the ECO codes we get the following distribution:

This is almost a copy of the first RR histogram, as expected from the reverse pairs.

If we use the opening 'family name' (using format FAMILY_NAME: VARIANT....) the top 3 are:
English - 27 times
Sicilian - 21 times
QGD, Queen's Pawn, Reti - 9 times each

Reverse pairs, openings

How many of the reverse pairs had the same opening by ECO? by full name?

More than half had different ECOs and more than 2/3 had different full name openings. The 2-move books allowed the engines some flexibility to choose how to proceed.

Reverse pairs, wins

64% of the pairs had a decisive result, either 2-0 or 1.5-0.5. Almost all of the drawn pairs consisted of two draws. There were only 3 pairs where each engine won once, i.e. two wins by the same color. These openings are suspected to be biased. However, looking at the games (Houdini-Ginkgo, Texel-Houdini, Nirvana-Ginkgo) it was well into the games that the advantage appeared, apparently very little to do with the first two moves.

Reverse pairs, same moves

How many plys did the engines play after book until the first divergence in the reverse games?

Divergence was usually within the first 2 moves (4 plys) after book. One pair (Gull-Nirvana, Four Knights: Italian Variation) held for 10 moves and one pair (Komodo-Stockfish, Trompowsky: 2...Ne4 3.Bf4 c5 4.d5 Qb6) held for 6 moves.