Symmetric matrix

From Encyclopedia of Mathematics
Revision as of 17:17, 7 February 2011 by (talk) (Importing text file)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

A square matrix in which any two elements symmetrically positioned with respect to the main diagonal are equal to each other, that is, a matrix that is equal to its transpose:

A real symmetric matrix of order has exactly real eigenvalues (counted with multiplicity). If is a symmetric matrix, then so are and , and if and are symmetric matrices of the same order, then is a symmetric matrix, while is symmetric if and only if .


Every square complex matrix is similar to a symmetric matrix. A real -matrix is symmetric if and only if the associated operator (with respect to the standard basis) is self-adjoint (with respect to the standard inner product). A polar decomposition factors a matrix into a product of a symmetric and an orthogonal matrix.

Let be a bilinear form on a vector space (cf. Bilinear mapping). Then the matrix of (with respect to the same basis in the two factors ) is symmetric if and only if is a symmetric bilinear form, i.e. .


[a1] F.R. [F.R. Gantmakher] Gantmacher, "The theory of matrices" , 1 , Chelsea, reprint (1959–1960) pp. Vol. 1, Chapt. IX; Vol. 2, Chapt. XI (Translated from Russian)
[a2] W. Noll, "Finite dimensional spaces" , M. Nijhoff (1987) pp. Sect. 2.7
How to Cite This Entry:
Symmetric matrix. Encyclopedia of Mathematics. URL:
This article was adapted from an original article by T.S. Pigolkina (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article