1
$二次型导数:frac{d(x^TAx)}{dx} = (A+A^T)x$
$且当A为对称矩阵时:A = A^T , frac{d(x^TAx)}{dx} = (A+A^T)x = 2Ax$
2
$ frac{d(A^Tx)}{dx} = frac{d(x^TA)}{dx} = A$
3
$u,v,x:n*1$
$ frac{dU^TV}{dx} = frac{partial U}{partial x}v+frac{partial V}{partial x}U$
4
$ frac{d(U+V)}{dx} = frac{dU}{dx}+frac{dV}{dx}$
分子分母布局，分母横向拉伸，分子纵向拉伸