How To Study As A Mathematics Major
《How To Study As A Mathematics Major》 · 第 7 页 · Section 0.2.5「Special types of square matrices」，定义段
A matrix $A\in M_n(F)$ is said to be symmetric if $A^T=A$, skew symmetric if $A^T=-A$, and orthogonal if $A^TA=I$; $A\in M_n(\mathbb C)$ is said to be Hermitian if $A^*=A$, skew Hermitian if $A^*=-A$, essentially Hermitian if $e^{i\theta}A$ is Hermitian for some $\theta\in\mathbb R$, unitary if $A^*A=I$, and normal if $A^*A=AA^*$.