Chess Random Opening Generator

[Leysan Torri]

I was looking at some recent games from the 2016 computer world chess championship. I realize that computers have opening books but how does the computer decide which opening and which continuation to go with? It seemed like, some losses were simply due to weak choices in the opening tree.

If you're asking how they choose from opening book moves in positions where multiple options are available, a common way to get a variety of openings would be to consult a random number generator (or pseudo-random number generator if we're being technical and pedantic). Maybe for white's first move the opening book says to play e4 40% of the time, d4 30%, c4 20%, Nf3 10%. If the program has access to a function that generates a random real (floating point) number r with a uniform distribution such that 0

If an opening book is meant for competing against other engines, of course the designers would want to avoid directing their engine to make "weak" moves. But how to determine which moves are weak? One way would be to look at the historical results of each move in a database of games (checking how many times the player who made that move won / lost / drew). For this you'd want a large games database to produce a statistically meaningful sample size for as many positions as possible, but you'd also want to filter it to only include games between sufficiently strong players / engines, which unfortunately reduces the sample size. Alternately or additionally, the designers could check the engine evaluations for positions in the database, but if the number of positions is very large (as it will be for any practically useful opening book), and since you want deep evaluations in order for this to be helpful, this approach would be extremely computationally demanding. A third approach would be to have a human expert (ideally a grandmaster) curate the database by hand. But again as the size of the opening book increases, this becomes impractical.

On the other hand, if the opening book is being used as a training tool for people to practice against, you might want the engine to play a wide variety of openings, some of them unsound. You might even want it to make occasional blunders that human players tend to make (a database of games between players of all levels would be useful for this purpose).

Fischer random chess, also known as Chess960 ('chess nine-sixty'), is a variation of the game of chess invented by the former world chess champion Bobby Fischer.[1] Fischer announced this variation on June 19, 1996, in Buenos Aires, Argentina.[2][3][4] Fischer random chess employs the same board and pieces as classical chess, but the starting position of the pieces on the players' home ranks is randomized, following certain rules. The random setup makes gaining an advantage through the memorization of openings impracticable; players instead must rely more on their skill and creativity over the board.

Randomizing the main pieces had long been known as shuffle chess, but Fischer random chess introduces new rules for the initial random setup, "preserving the dynamic nature of the game by retaining bishops of opposite colors for each player and the right to castle for both sides".[5] The result is 960 unique possible starting positions.

In 2008, FIDE added Chess960 to an appendix of the Laws of Chess.[8] The first world championship officially sanctioned by FIDE, the FIDE World Fischer Random Chess Championship 2019, brought additional prominence to the variant. It was won by Wesley So.[9] In 2022, Hikaru Nakamura became the new champion.[10]

Black's pieces are placed equal-and-opposite to White's pieces. (For example, if the white king is randomly determined to start on f1, then the black king is placed on f8.) Pawns are placed on the players' second ranks as in classical chess.

Usually, the players accept the conditions of the organizer to generate the starting position with software. If the software is not available or the players do not accept it, there are many ways to generate a random starting position with equal probability. This requires choosing a number randomly between 0 and 959 inclusive; this number is then used as an index to the Fischer random chess numbering scheme.

The variant has held a number of different names. It was originally known as "Fischerandom" or "Fischerandom chess", the name given by Fischer. "Chess960" is used by FIDE in its Laws of Chess.[13]

Hans-Walter Schmitt, chairman of the Frankfurt Chess Tigers e.V. and an advocate of the variant, started a brainstormingprocess for creating a new name, which had to meet the requirements of leading grandmasters; specifically, the new name and its parts:

Reinhard Scharnagl, another proponent of the variant, advocated the term "FullChess". Today he uses FullChess, however, to refer to variants which consistently embed classical chess (e.g. Chess960 and similar variants). He recommends the name Chess960 for the variant in preference to Fischer random chess.

Starting 2019, whenever the Saint Louis Chess Club hosts Fischer Random chess tournaments, their tournaments are called Chess 9LX,[14][15] where '9LX' is a combination of the Arabic numeral 9 and the Roman numeral LX (60), a possible reference to how the number '960' is often read as 'nine-sixty' instead of 'nine hundred sixty' when talking about 'chess960'.

As in classical chess, each player may castle once per game, moving both the king and a rook in a single move; however, the castling rules were reinterpreted in Fischer random chess to support the different possible initial positions of king and rook. After castling, the final positions of king and rook are the same as in classical chess, namely:

FIDE's recommended procedure for castling unambiguously is first to move the king outside the playing area next to its final square, then to move the rook to its final square, then to move the king to its final square. Another recommendation is to verbally announce the intent to castle before doing so.[7]

The study of openings in Fischer random chess is in its infancy,[26][27][28][29] but fundamental opening principles still apply, including: protect the king, control the central squares (directly or indirectly), and develop rapidly, starting with the less valuable pieces.

Unprotected pawns may also need to be dealt with quickly. Many starting positions have unprotected pawns, and some starting positions have up to two that can be attacked on the first move. For example, in some Fischer random chess starting positions (see diagram), White can attack an unprotected black pawn on the first move, whereas in classical chess it takes two moves for White to attack, and there are no unprotected pawns.

It has been argued that two games should be played from each starting position, with players alternating colors, since the advantage offered to White in some initial positions may be greater than in classical chess.[30]

However, Sesse[23][24] (which used Stockfish 9) evaluated the starting positions to be between 0.00 and 0.57, with an average of 0.18 pawns advantage for White, where BBNNRKRQ (SP 80) was the most unbalanced position. The standard chess starting position (SP 518) was evaluated at 0.22. With a standard deviation of 0.0955, 923 starting positions lie within two standard deviations of the mean i.e. between 0 and 0.371. Hence, on average a Fischer Random starting position is 22.2% less unbalanced than the standard starting position.

The concept of random chess, also known as shuffle chess, was first proposed by the Dutch chess enthusiast Philip Julius van Zuylen van Nijevelt (1743-1826). In his renowned treatise on chess, La Supriorit aux checs, published in 1792, Van Zuylen van Nijevelt articulated his disdain for the repetitive patterns often found in standard chess openings. He proposed the idea of randomizing the starting positions of the main pieces to create a vast array of unique situations, eliminating the possibility of pre-game memorization or extensive opening theory. Van Zuylen van Nijevelt's book, with its full title La Supriorit aux checs mise la porte de tout le monde, et particulirement des dames qui aiment cet amusement ("Superiority in Chess brought into the reach of all, and particularly of ladies who love that amusement"), gained significant popularity and was reprinted several times. Its influence extended beyond the Dutch-speaking world, as it was subsequently translated into multiple languages, spreading the idea of randomizing the initial positions of chess pieces to a wider audience. This early conception of random chess by Van Zuylen van Nijevelt laid the foundation for what later became known as Fischer random chess, a variant that gained prominence in the 20th century.

Van Zuylen van Nijevelt's innovative approach to chess not only offered a solution to the repetitive nature of traditional openings but also paved the way for the exploration of chess variants that deviate from the conventional starting position. His quote within La Supriorit aux checs emphasizes the core principle behind random chess, stating, "This produces a huge number of different situations, so that no one can study them beforehand," reflecting his desire to introduce an element of unpredictability and originality into the game of chess. The legacy of Van Zuylen van Nijevelt's contributions to the evolution of chess remains significant, with his early insights serving as a cornerstone for the development of various randomized chess variants, including Fischer random chess and its contemporary iterations.[31][32][33]

The pioneering work of Van Zuylen van Nijevelt found continued development through the efforts of his nephew, the Jonkheer Elias van der Hoeven (1778-1854), a Dutch diplomat. Van der Hoeven took the concept of shuffle chess further, potentially sharing his insights with Aaron Alexandre, evident from Alexandre's incorporation of the theory into his Encyclopdie des checs in 1837.

The earliest documented games of shuffle chess were played between Van der Hoeven and Alexandre in Mannheim in 1842, with Alexandre emerging as the victor with a score of 3-0. One of these games is preserved in Sissa, the Netherlands' first long-standing chess journal, demonstrating an initial position with two advanced pawns on each side. A later game played by Van der Hoeven was against Baron von der Lasa (1818-1899), adhering more closely to the contemporary rules of random chess, except for the monochromatic bishop pairs.

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