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The Cartesian square of a set X is the Cartesian product X 2 = X × X. An example is the 2-dimensional plane R 2 = R × R where R is the set of real numbers: [1] R 2 is the set of all points (x,y) where x and y are real numbers (see the Cartesian coordinate system).
In set theory, a Cartesian product is a mathematical operation which returns a set (or product set) from multiple sets. That is, for sets A and B, the Cartesian product A × B is the set of all ordered pairs (a, b) —where a ∈ A and b ∈ B. [5] The class of all things (of a given type) that have Cartesian products is called a Cartesian ...
Here, vec(X) denotes the vectorization of the matrix X, formed by stacking the columns of X into a single column vector. It now follows from the properties of the Kronecker product that the equation AXB = C has a unique solution, if and only if A and B are invertible (Horn & Johnson 1991, Lemma 4.3.1).
In category theory, the product of two (or more) objects in a category is a notion designed to capture the essence behind constructions in other areas of mathematics such as the Cartesian product of sets, the direct product of groups or rings, and the product of topological spaces.
Ternary relations may also be referred to as 3-adic, 3-ary, 3-dimensional, or 3-place. Just as a binary relation is formally defined as a set of pairs , i.e. a subset of the Cartesian product A × B of some sets A and B , so a ternary relation is a set of triples, forming a subset of the Cartesian product A × B × C of three sets A , B and C .
In the first case, the projection π 1 extracts the x index while π 2 forgets the index, leaving elements of Y. This example motivates another way of characterizing the pullback: as the equalizer of the morphisms f ∘ p 1, g ∘ p 2 : X × Y → Z where X × Y is the binary product of X and Y and p 1 and p 2 are the natural projections. This ...
The product X×Y is the Cartesian product of X and Y, and Z Y is the set of all functions from Y to Z. The adjointness is expressed by the following fact: the function f : X × Y → Z is naturally identified with the curried function g : X → Z Y defined by g ( x )( y ) = f ( x , y ) for all x in X and y in Y .
The lexicographic combination of two total orders is a linear extension of their product order, and thus the product order is a subrelation of the lexicographic order. [3] The Cartesian product with the product order is the categorical product in the category of partially ordered sets with monotone functions. [7]