2.矩阵的迹&转置&对称矩阵2.1矩阵的迹定义：\(n\timesn\)矩阵主对角线上元素的总和称为\(矩阵的迹\)矩阵X的迹记为\(tr(X)\)示例：设存在以下\(n\timesn\)的矩阵：\[X_{n\timesn}=\begin{bmatrix}x_{11}&x_{12}&x_{13}&...&x_{1n}\\x_{21}&x_{22}&