Questions tagged [latin-square]

For questions on or pertaining to Latin squares.

In combinatorics and in experimental design, a Latin square is an $n \times n$ array filled with $n$ different symbols, each occurring exactly once in each row and exactly once in each column.

For example, the two Latin squares of order two are given by $$\begin{pmatrix} 1 & 2 \\ 2 & 1 \end{pmatrix}\qquad\text{and}\qquad\begin{pmatrix} 2 & 1 \\ 1 & 2 \end{pmatrix}$$

  • Sudoku is a special case of a Latin square.
  • In the design of experiments, Latin squares are a special case of row-column designs for two blocking factors.
  • Many row-column designs are constructed by concatenating Latin squares.
  • In algebra, Latin squares are generalizations of groups.
  • In fact, Latin squares are characterized as being the multiplication tables (Cayley tables) of quasigroups.
  • A binary operation whose table of values forms a Latin square is said to obey the Latin square property.

References:

https://en.wikipedia.org/wiki/Latin_square#Applications

http://mathworld.wolfram.com/LatinSquare.html

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Are there complete Graeco-Latin squares?

Are there two orthogonal complete Latin squares of any order greater than 1? If so, what is the smallest order for which they exist? (A Latin square of order $n$ is an $n\times n$ array of symbols $\{ s_1\ldots s_n \}$ such that each of the symbols…
MJD
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Generate Random Latin Squares

I'm looking for algorithms to generate randomized instances of Latin squares. I found only one paper: M. T. Jacobson and P. Matthews, Generating uniformly distributed random Latin squares, J. Combinatorial Design 4 (1996), 405-437 Is there any…
user14947
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Covering pairs with permutations

Consider an $n \times n$ matrix $M_n$ with the following properties: Each row is a permutation of $A_n \equiv \{1, 2, ..., n\}$. Every ordered pair $(i,j)$, $i,j \in A_n$, $i \neq j$, appears as a horizontally adjacent pair in $M_n$ exactly once…
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Can a solved Sudoku game have an invalid region if all rows and columns are valid?

Given a $9 \times 9$ solved Sudoku game with $3 \times 3$ regions, is it possible that one (or more) of the regions are invalid if all rows and columns are valid (i.e. have a unique sequence of $1-9$)?
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Maximum determinant of Latin squares

I strongly conjecture that the maximum absolute determinant of a Latin square can be attained by a circulant matrix. For example, $$\pmatrix {5&4&2&3&1 \\ 1&5&4&2&3 \\ 3&1&5&4&2 \\ 2&3&1&5&4 \\ 4&2&3&1&5}$$ has determinant $2325$, which is indeed…
Peter
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The Hardest Sudoku Puzzle

I was playing a casual game of Sudoku today when a friend came by and asked "What's the hardest game of Sudoku possible?" My response: "A Sudoku puzzle with the minimal amount of starting numbers where the puzzle is still solvable." However, I am…
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Color an $n\times n$ square with $n$ colors

How many ways is there to color an $n\times n$ square grid with $n$ colors such that each column and each row contains exactly one $1\times 1$ square of each color? And how many ways if the same is required of the two diagonals?
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How many ways to colour a $4 \times 4$ grid using four colours subject to three constraints

In how many ways can a $4 \times 4$ square grid be coloured using four different colours so that no colour is repeated in any row, column, or along the two main diagonals. For clarity, one valid solution to this problem is shown below. I am after…
omegadot
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Is there a sudoku (Latin Square Pattern) state in a Rubik's cube $6\times6\times6?$

Suppose, Initial state Rubik's Cube 6x6x6 444444 444444 444444 444444 444444 444444 000000 111111 222222 333333 000000 111111 222222 333333 000000 111111 222222 333333 000000 111111 222222 333333 000000 111111 222222 333333 000000 111111 222222…
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When is a Sudoku like table solvable

Given a $n\times n$ table is it possible to fill each cell with one of the numbers $1,2,3,\cdots,n$ such that in each column,each row and each diagonal (i.e Denoting $(x,y)$ as number of column and row $(2,1)$ and $(1,2)$ form the first diagonal)…
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How many Sudoku puzzles are there with at least one solution?

A Sudoku puzzle is a 9 by 9 matrix of blanks(which we can represent as 0), and elements of the set {1,2,3,4,5,6,7,8,9}. How many Sudoku puzzles are there with at least one solution. Yes, I am even counting grids with no blanks.
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Formula for the number of latin squares of size $n$?

Is there a "easy to compute" formula for the number of Latin Squares or the number of reduced Latin squares of size $n$?
croq67
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Transforming a latin square into a sudoku

Can any $9\times 9$ - Latin Square be transformed into a sudoku by just exchanging rows and columns (it is allowed to mix row- and column-exchanges arbitarily and there is no limit for the number of the exchanges) ?
Peter
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8
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symmetric latin square of order 5

My textbook said if a latin square of order 5 is idempotent and had a 2 in the (1,3) entry, it could not be completed as a symmetric square. But isn't this one such square? Or do I have the definition of "symmetric" wrong? 1 4 2 5 3 4 2 …
user81055
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A balanced latin rectangle (more rows than columns)

In psychology we sometimes use balanced latin squares for the order of our tests to counterbalance first-order carry-over effects (fatigue, learning, etc.) . For our current study we want to pretest 12 stimuli (let's call them A-F) to see whether…
Ruben
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