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Four-dimensional space (4D) is the mathematical extension of the concept of three-dimensional space (3D). Three-dimensional space is the simplest possible abstraction of the observation that one needs only three numbers, called dimensions, to describe the sizes or locations of objects in the everyday world.
Johan Ernest Mebius (2005). "A matrix-based proof of the quaternion representation theorem for four-dimensional rotations". arXiv: math/0501249. Johan Ernest Mebius (2007). "Derivation of the Euler-Rodrigues formula for three-dimensional rotations from the general formula for four-dimensional rotations". arXiv: math/0701759.
Even though every quaternion can be viewed as a vector in a four-dimensional vector space, it is common to refer to the vector part as vectors in three-dimensional space. With this convention, a vector is the same as an element of the vector space R 3 . {\displaystyle \mathbb {R} ^{3}.} [ b ]
A unit tesseract has side length 1, and is typically taken as the basic unit for hypervolume in 4-dimensional space. The unit tesseract in a Cartesian coordinate system for 4-dimensional space has two opposite vertices at coordinates [0, 0, 0, 0] and [1, 1, 1, 1], and other vertices with coordinates at all possible combinations of 0 s and 1 s.
Given two inertial or rotated frames of reference, a four-vector is defined as a quantity which transforms according to the Lorentz transformation matrix Λ: ′ =. In index notation, the contravariant and covariant components transform according to, respectively: ′ =, ′ = in which the matrix Λ has components Λ μ ν in row μ and column ν, and the matrix (Λ −1) T has components Λ ...
In 4-space n = 4, the four eigenvalues are of the form e ±iθ, e ±iφ. The null rotation has θ = φ = 0 . The case of θ = 0, φ ≠ 0 is called a simple rotation , with two unit eigenvalues forming an axis plane , and a two-dimensional rotation orthogonal to the axis plane.
An arbitrary four-dimensional rotation has six degrees of freedom, with each matrix contributing three of these six degrees of freedom. Since the generators of the four-dimensional rotations can be represented by pairs of quaternions (as follows), all four-dimensional rotations can also be represented.
For example, if A is a 3-by-0 matrix and B is a 0-by-3 matrix, then AB is the 3-by-3 zero matrix corresponding to the null map from a 3-dimensional space V to itself, while BA is a 0-by-0 matrix. There is no common notation for empty matrices, but most computer algebra systems allow creating and computing with them.