Editing Square matrix (section)

===Normal matrix===
A real or complex square matrix <math>A</math> is called ''[[normal matrix|normal]]'' if {{nowrap|<math>A^* A = AA^*</math>.}}  If a real square matrix is symmetric, skew-symmetric, or orthogonal, then it is normal. If a complex square matrix is Hermitian, skew-Hermitian, or unitary, then it is normal. Normal matrices are of interest mainly because they include the types of matrices just listed and form the broadest class of matrices for which the [[spectral theorem]] holds.<ref>Artin, ''Algebra'', 2nd edition, Pearson, 2018, section 8.6.</ref>