1. [[Hermitian matrices]] >[!Info] >For notation, we use capital letter for matrix and operator, like $A, T, H$, and $u, v, x$ for vector and scalar. >The inner product representation is a bit different from [[Tensor calculus and linear algebra#Inner product and the Gram matrix]], but as written later. We use $\langle \cdot,\cdot\rangle$ for inner product.