矩阵求导 ∇X(XAXT)=AXT+XA\nabla_{\bm{X}} (\bm{XAX}^{\text{T}})=\bm{AX}^{\text{T}}+\bm{XA}∇X(XAXT)=AXT+XA 矩阵迹求导 tr(AB)=tr(BA)\rm{tr}(\bm{AB}) =\rm{tr}(\bm{BA})tr(AB)=tr(BA)