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In linear algebra, the adjugate or classical adjoint of a square matrix A, adj(A), is the transpose of its cofactor matrix. [1] [2] It is occasionally known as adjunct matrix, [3] [4] or "adjoint", [5] though that normally refers to a different concept, the adjoint operator which for a matrix is the conjugate transpose.
Definition Comments Adjugate matrix: Transpose of the cofactor matrix: The inverse of a matrix is its adjugate matrix divided by its determinant: Augmented matrix: Matrix whose rows are concatenations of the rows of two smaller matrices: Used for performing the same row operations on two matrices Bézout matrix
The conjugate transpose "adjoint" matrix should not be confused with the adjugate, (), which is also sometimes called adjoint. The conjugate transpose of a matrix A {\displaystyle \mathbf {A} } with real entries reduces to the transpose of A {\displaystyle \mathbf {A} } , as the conjugate of a real number is the number itself.
A matrix with entries in a field is invertible precisely if its determinant is nonzero. This follows from the multiplicativity of the determinant and the formula for the inverse involving the adjugate matrix mentioned below. In this event, the determinant of the inverse matrix is given by
Conjugate transpose of a matrix in linear algebra; Adjugate matrix, related to its inverse; Adjoint equation; The upper and lower adjoints of a Galois connection in order theory; The adjoint of a differential operator with general polynomial coefficients; Kleisli adjunction; Monoidal adjunction; Quillen adjunction; Axiom of adjunction in set theory
In matrix calculus, Jacobi's formula expresses the derivative of the determinant of a matrix A in terms of the adjugate of A and the derivative of A. [1]If A is a differentiable map from the real numbers to n × n matrices, then
Let A be an n × n matrix with entries in a field F. Then = = where adj(A) denotes the adjugate matrix, det(A) is the determinant, and I is the identity matrix. If det(A) is nonzero, then the inverse matrix of A is
The adjugate has sometimes been called the "adjoint", but that terminology is ambiguous and is not used in Wikipedia. Today, "adjoint" normally refers to the conjugate transpose. A more generic example is this: given matrix A its adjoint is ... The article is clear to me: "adjugate" resolves an ambiguity in the literature.