Gershgorin circle theorem

The Gershgorin Circle Theorem is a result in linear algebra that provides a method for locating the eigenvalues of a square matrix. It is particularly useful when analyzing the spectral properties of a matrix without explicitly calculating its eigenvalues. The theorem states that for any \( n \times n \) complex matrix \( A = [a_{ij}] \), the eigenvalues of \( A \) lie within certain circles in the complex plane defined by the rows of the matrix.