Openings FAQ

TCEC Openings FAQ

• Q: Why do TCEC chess games not start from the opening position?

• A: The answer is rooted on our site’s general objectives, past experience trying different play formats, and our judgment on what makes an entertaining competition and therefore a successful website.

· Our primary goal is to provide our web audience with fair and entertaining chess competitions.

· We believe that a champion chess program ought to be able to perform well in a wide variety of opening systems, not merely those that it favors. This approach is different from human tournaments by design.

· We see the traditional opening position as merely one position out of many thousands that might present a chess program with a challenge. What distinguishes the opening position in computer chess is that it is relatively balanced, meaning it has a high probability of resulting in a draw when played by top competitors at long time controls on very strong hardware.

· Many chess programs repeatedly play a given position the same way. When two such programs meet, they invariably produce repetitive contests. A 100-game test we ran between leading engines some time ago resulted in 88% of the games concentrating into just five ECOs. Such outcomes frustrate the majority’s desire for entertaining chess.

· The fact that different competitors must cope with an unpredictable and unequal set of openings does add an element of chance to the competition. Mitigating this chance element,

1) competitors play the selected openings from both sides of the board in consecutive games,

2) the length of our season tournaments assures a wide variety of openings, and

3) the openings tend, over time, to balance out in terms of drawishness and bias.

This latter point underscores the principal risk to our approach, namely, that competitors can be saddled with openings that are too draw-prone or too one-sided, resulting in game-pairs that fail to differentiate the competitors on the cross-table. Our openings team is skilled at selecting opening positions that are neither hopelessly draw-prone nor so one-sided that the weaker side has no chance of holding the draw.

• Q: Who selects the openings?

• A: TCEC has a team working on the openings books, supervised by Nelson Hernandez.

For S20 the Qualifying League (QL) the games shall be 'bookless', i.e. games starting from the opening position.

Leagues 4 and 3 will use short books, 2 and 4 moves, respectively, created by Nelson Hernandez (aka CatoTheYounger_TCEC). These shall be common chess openings, played randomly.

League 2 openings will be selected for a second season by Eduardo Sauceda (aka Cookie Monster). These shall be of varied length, played in order, and will feature substantially biased openings.

League 1 openings will be selected by newcomer to the book team Bastiaan J. Braams (aka bjbraams). These also shall be of varied length, played in order, and will feature substantially biased openings.

Premier Division openings will be selected by Nelson Hernandez, now serving TCEC for his 16th season. This new book shall be of fixed length (16 plies), played randomly, and will feature the most biased openings Nelson has ever dared to include in a book. The primary emphasis will be bias, confirmed across multiple engines, and not ECO-diversity as has been the case in past seasons.

The S20 Superfinal will once again be selected by esteemed computer chess veteran Jeroen Noomen (aka Jeroen_TCEC), now performing TCEC SuFi service for his 12th season. Jeroen provides separate commentary on his picks each season.

• Q: How are the openings structured?

• A: Each seasonal tournament, from the Qualifying League through the Superfinal, has a different opening ‘book’ that issues starting positions:

Tournament	Book	Author	Book Length	# Positions	Selection	Opening Bias	Perpetual
Qualifying League	Bookless	none	0 moves	1	sequential	none	yes
League 4	Book A	Nelson	2 moves	1000	random	none	yes
League 3	Book B	Nelson	4 moves	1000	random	none	yes
League 2	Book C	Eduardo	varied	45	sequential	moderate/high	no
League 1	Book D	Bastiaan	varied	56	sequential	high	no
Premier Division	Book E	Nelson	8 moves	1000+	random	high	yes
Superfinal	SuFiBook	Jeroen	varied	50	sequential	high/very high	no
Cup Final/Bronze	Book F	Jeroen	varied	500+	random	high/very high	yes

# Positions signifies the number of unique positions contained within each book.

Selection indicates how positions contained within the books are selected. (Thus, in League 1 there are 1,000 unique positions in the book which are chosen at random prior to each new game-pair.)

Opening Bias indicates the degree to which the average opening is skewed to favor one color or the other. (An exception to this is that Jeroen sometimes starts the Superfinal with two bookless games.)

Perpetual indicates that the first four leagues get starting positions from the same book from season to season whereas Superfinal books are for one-time use with a new book each season.

• Q: What do you mean when you say you “bias” openings, and why do you do it?

• A: Bias is the degree to which a particular opening, or a set of openings, seem to favor one side or the other according to empirical data (historical outcomes) and evaluative data (deep analysis from top engines).

The opening position typically offers white a slightly favorable evaluation of +0.15 to +0.20 on traditional chess programs where the “comtempt” setting is neutralized. Low or zero bias in an opening book makes little difference in a tournament where time controls are shorter and contestants have a wider range of Elos. In that case, there will be ample decisive games.

However, if very strong, closely matched programs are playing at long time controls with no bias that invites a draw-rate approaching 90-95%. To combat this, we introduce bias in League 2 and ramp it up from there as we progress through the season. Our four different book authors each have different approaches to striking a balance between too much and not enough.

• Q: To what degree do you bias openings?

• A: This is hard to quantify precisely because different engines scale their evaluations differently, plus different authors take different approaches, but at very high bias levels one color will typically have a pawn advantage at book-exit, more or less. In League 2 it isn't quite so high. In the Premier Division, a score of +/-0.50 to +/-0.80 is more common. Sometimes he will deviate from these guidelines to the upside or downside to satisfy opening variety goals.

In each season’s Superfinal Jeroen has a free hand to do whatever he thinks will result in an interesting and varied contest. Sometimes his book-exit evaluations will exceed +/-1.00; sometimes he will offer speculative gambits. His goal is to keep the draw-rate in the 65-80% range each season without a surfeit of one-sided openings.

• Q: Why such an aversion to draws? If chess is naturally drawish, why try to distort that reality?

• A: The ultimate objective of a tournament is to crown a deserving champion. If you play 100 Superfinal games and 95 of them are draws you will not only drive away much of your audience, you wind up crowning a champion that may have only scored three wins against his opponent’s two. In that event, statistics tell us that the winner may have qualified for the Superfinal based on skill but may have won it entirely on luck. A greater number of decisive game-pairs (i.e. 1.5-0.5, 2-0) reduce the probability of luck being the critical factor as there is a greater chance of one engine pulling away for a clear win.

While we do not object to close contests in the Superfinal — on the contrary — we would prefer as many decisive (i.e. not tied) game-pairs as possible, as this way the strongest competitor will have the greatest chance to demonstrate all-around superiority. Plus, it is more entertaining!

• Q: How long can you maintain your targeted 65-80% draw-rate in the Superfinal when engines are continually improving?

• A: Draw abatement will definitely be more challenging as the competitors increase in strength in the years ahead. A mental comparison between today’s leading chess programs and those of ten years ago, combined with extrapolation into the future, points to a time where something will have to give.

• Q: What impact will the advent of neural nets and their very different evaluative frame of reference have on your opening set selections?

• A: This is impossible to answer as each executable/neural net pairing is unique and presents a different behavioral profile with respect to strength, resistance to draws, evaluation volatility and reliability, etc. The whole field of AI is undergoing rapid development with innovations happening continually; the competitive landscape changes from season to season in surprising ways.

That said, TCEC’s history is one of gradual evolution in response to emerging trends and practical experience; we expect that to continue.