Quaternionic matrix

Last updated June 09, 2021

A quaternionic matrix is a matrix whose elements are quaternions.

Matrix operations

The quaternions form a noncommutative ring, and therefore addition and multiplication can be defined for quaternionic matrices as for matrices over any ring.

Addition. The sum of two quaternionic matrices A and B is defined in the usual way by element-wise addition:

(A+B)_{ij}=A_{ij}+B_{ij}.\,

Multiplication. The product of two quaternionic matrices A and B also follows the usual definition for matrix multiplication. For it to be defined, the number of columns of A must equal the number of rows of B. Then the entry in the ith row and jth column of the product is the dot product of the ith row of the first matrix with the jth column of the second matrix. Specifically:

(AB)_{ij}=\sum _{s}A_{is}B_{sj}.\,

For example, for

U={\begin{pmatrix}u_{11}&u_{12}\\u_{21}&u_{22}\\\end{pmatrix}},\quad V={\begin{pmatrix}v_{11}&v_{12}\\v_{21}&v_{22}\\\end{pmatrix}},

the product is

UV={\begin{pmatrix}u_{11}v_{11}+u_{12}v_{21}&u_{11}v_{12}+u_{12}v_{22}\\u_{21}v_{11}+u_{22}v_{21}&u_{21}v_{12}+u_{22}v_{22}\\\end{pmatrix}}.

Since quaternionic multiplication is noncommutative, care must be taken to preserve the order of the factors when computing the product of matrices.

The identity for this multiplication is, as expected, the diagonal matrix I = diag(1, 1, ... , 1). Multiplication follows the usual laws of associativity and distributivity. The trace of a matrix is defined as the sum of the diagonal elements, but in general

\operatorname {trace} (AB)\neq \operatorname {trace} (BA).

Left scalar multiplication, and right scalar multiplication are defined by

(cA)_{ij}=cA_{ij},\qquad (Ac)_{ij}=A_{ij}c.\,

Again, since multiplication is not commutative some care must be taken in the order of the factors.^[1]

Determinants

There is no natural way to define a determinant for (square) quaternionic matrices so that the values of the determinant are quaternions.^[2] Complex valued determinants can be defined however.^[3] The quaternion a + bi + cj + dk can be represented as the 2×2 complex matrix

{\begin{bmatrix}~~a+bi&c+di\\-c+di&a-bi\end{bmatrix}}.

This defines a map Ψ_mn from the m by n quaternionic matrices to the 2m by 2n complex matrices by replacing each entry in the quaternionic matrix by its 2 by 2 complex representation. The complex valued determinant of a square quaternionic matrix A is then defined as det(Ψ(A)). Many of the usual laws for determinants hold; in particular, an n by n matrix is invertible if and only if its determinant is nonzero.

Applications

Quaternionic matrices are used in quantum mechanics ^[4] and in the treatment of multibody problems.^[5]

Related Research Articles

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References

↑ Tapp, Kristopher (2005). Matrix groups for undergraduates. AMS Bookstore. pp. 11 ff. ISBN 0-8218-3785-0.
↑ Helmer Aslaksen (1996). "Quaternionic determinants". The Mathematical Intelligencer . 18 (3): 57–65. doi:10.1007/BF03024312. S2CID 13958298.
↑ E. Study (1920). "Zur Theorie der linearen Gleichungen". Acta Mathematica (in German). 42 (1): 1–61. doi: 10.1007/BF02404401 .
↑ N. Rösch (1983). "Time-reversal symmetry, Kramers' degeneracy and the algebraic eigenvalue problem". Chemical Physics . 80 (1–2): 1–5. doi:10.1016/0301-0104(83)85163-5.
↑ Klaus Gürlebeck; Wolfgang Sprössig (1997). "Quaternionic matrices". Quaternionic and Clifford calculus for physicists and engineers . Wiley. pp. 32–34. ISBN 978-0-471-96200-7.

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[1] Tapp, Kristopher (2005). Matrix groups for undergraduates. AMS Bookstore. pp. 11 ff. ISBN 0-8218-3785-0.

[2] Helmer Aslaksen (1996). "Quaternionic determinants". The Mathematical Intelligencer . 18 (3): 57–65. doi:10.1007/BF03024312. S2CID 13958298.

[3] E. Study (1920). "Zur Theorie der linearen Gleichungen". Acta Mathematica (in German). 42 (1): 1–61. doi: 10.1007/BF02404401 .

[4] N. Rösch (1983). "Time-reversal symmetry, Kramers' degeneracy and the algebraic eigenvalue problem". Chemical Physics . 80 (1–2): 1–5. doi:10.1016/0301-0104(83)85163-5.

[5] Klaus Gürlebeck; Wolfgang Sprössig (1997). "Quaternionic matrices". Quaternionic and Clifford calculus for physicists and engineers . Wiley. pp. 32–34. ISBN 978-0-471-96200-7.

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v t e Matrix classes
Explicitly constrained entries	(0,1) Alternant Anti-diagonal Anti-Hermitian Anti-symmetric Arrowhead Band Bidiagonal Binary Bisymmetric Block-diagonal Block Block tridiagonal Boolean Cauchy Centrosymmetric Conference Complex Hadamard Copositive Diagonally dominant Diagonal Discrete Fourier Transform Elementary Equivalent Frobenius Generalized permutation Hadamard Hankel Hermitian Hessenberg Hollow Integer Logical Metzler Moore Nonnegative Pentadiagonal Permutation Persymmetric Polynomial Quaternionic Signature Single-entry Skew-Hermitian Skew-symmetric Skyline Sparse Sylvester Symmetric Toeplitz Triangular Tridiagonal Unitary Vandermonde Walsh Z
Constant	Exchange Hilbert Identity Lehmer Of ones Pascal Pauli Redheffer Shift Zero
Conditions on eigenvalues or eigenvectors	Companion Convergent Defective Diagonalizable Hurwitz Positive-definite Stieltjes
Satisfying conditions on products or inverses	Congruent Idempotent or Projection Invertible Involutory Nilpotent Normal Orthogonal Unimodular Unipotent Totally unimodular Weighing
With specific applications	Adjugate Alternating sign Augmented Bézout Carleman Cartan Circulant Cofactor Commutation Confusion Coxeter Distance Duplication and elimination Euclidean distance Fundamental (linear differential equation) Generator Gram Hessian Householder Jacobian Moment Payoff Pick Random Rotation Seifert Shear Similarity Symplectic Totally positive Transformation X–Y–Z
Used in statistics	Centering Correlation Covariance Design Doubly stochastic Fisher information Hat Precision Stochastic Transition
Used in graph theory	Adjacency Biadjacency Degree Edmonds Incidence Laplacian Seidel adjacency Tutte
Used in science and engineering	Cabibbo–Kobayashi–Maskawa Density Fundamental (computer vision) Fuzzy associative Gamma Gell-Mann Hamiltonian Irregular Overlap S State transition Substitution Z (chemistry)
Related terms	Jordan normal form Linear independence Matrix exponential Matrix representation of conic sections Perfect matrix Pseudoinverse Quaternionic matrix Row echelon form Wronskian
List of matrices Category:Matrices