2. Square array. There are many kinds of ancient arrays, such as square array, circular array, yan zhen, hook array and so on.

3, refers to the mahjong bureau. Four people play against each other. Before the start of the game, each person manages seventeen or eighteen piers to form a phalanx, so it is called.

4. Mathematically, it refers to a matrix with the same number of rows and columns, that is, a square matrix. Tactically, you can refer to the Greek phalanx and the Roman phalanx (fish scale array). Militarily, the Macedonian phalanx in ancient Greece and Mk 15/ 16 in the US Navy? Square array short-range weapon system.

Extended data

The origin of Sudoku can be traced back to Europe in18th century. It is said that Fay the Great of Prussia once set up a guard of honor. The honor guard has 36 officers from 6 units. Each unit has colonel 1 name, lieutenant 1 name, major 1 name, captain 1 name, lieutenant 1 name and second lieutenant 1 name.

He hoped that the 36 officers would be arranged in a 6×6 phalanx, and the six officers in each row and column of the phalanx would come from different troops and have different ranks. Later, he went to consult the famous Swiss mathematician Euler. Euler found this an impossible task.

If n×n officers of n ranks from n units can be arranged in a square, and each row and column has n officers of different ranks from different units, then this square is called an orthogonal Latin square.

Euler guessed that n = 2,6, 10, 14, 18, …

Orthogonal latin squares matrix does not exist. However, in 1960s, people used computers to create orthogonal latin squares with n= 10, which overturned Euler's conjecture. Now it is known that all orthogonal Latin squares exist except n = 2,6, and there are many construction methods.

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