关于矩阵导数的几个性质的证明

关于矩阵导数的几个性质的证明

  • (1) A t r ( A B ) = B T \nabla_Atr(AB)=B^T
  • (2) A t r ( A B A T C ) = C A B + C T A B T \nabla_Atr(ABA^TC)=CAB+C^TAB^T
  • (3) A A = A ( A 1 ) T \nabla_A|A|=|A|(A^{-1})^T
    Proof of (1)
    Let A = [ a 1 ,   , a n ] , B = [ b 1 b n ] A=[a_1,\cdots,a_n],B=\begin{bmatrix}b_1'\\\vdots\\b_n'\end{bmatrix}
    Then A t r ( A B ) = A t r ( i = 1 n a i b i ) = i = 1 n A t r ( a i b i ) \nabla_Atr(AB)=\nabla_Atr(\sum_{i=1}^{n}a_ib_i')=\sum_{i=1}^{n}\nabla_Atr(a_ib_i')
    A t r ( a i b i ) = A t r ( [ a 1 i a m i ] [ b i 1 ,   , b i m ] ) = A j = 1 m a j i b i j = [ 0 ,   , b i ,   , 0 ] \nabla_Atr(a_ib_i')=\nabla_Atr(\begin{bmatrix}a_{1i}\\\vdots\\a_{mi}\end{bmatrix}[b_{i1},\cdots,b_{im}])=\nabla_A\sum_{j=1}^ma_{ji}b_{ij}=[0,\cdots,b_i,\cdots,0]
    so A t r ( A B ) = i = 1 n A t r ( a i b i ) = [ b 1 ,   , b n ] = B T \nabla_Atr(AB)=\sum_{i=1}^n\nabla_Atr(a_ib_i')=[b_1,\cdots,b_n]=B^T
    Proof of 2
    这是在知乎上看到的证明https://www.zhihu.com/question/56412790

    Proof of (3)
    A = j A i j A i j |A|=\sum_jA_{ij}A_{ij}' , A i j A_{ij}' 是A的ij位置对应的代数余子式
    于是 A A i j = A i j \frac{\partial |A|}{\partial A_{ij}}=A_{ij}'
    所以 A A = A = ( A ) T = ( A A 1 ) T = A ( A 1 ) T \nabla_A|A|=A'=(A^*)^T=(|A|A^{-1})^T=|A|(A^{-1})^T
    第三个等号是因为 A A = A E n AA^*=|A|E_n

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转载自blog.csdn.net/a1109885671/article/details/81226176
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