1. http://blog.sina.com.cn/s/blog_6c17a3a00100qg5w.html (矩阵,向量求导公式)
2.https://blog.csdn.net/crazy_scott/article/details/80557814 (矩阵的迹)
3.https://blog.csdn.net/nomadlx53/article/details/50849941 (矩阵:布局)
4. https://en.wikipedia.org/wiki/Matrix_calculus#Scalar-by-vector_identities (wiki)