矩阵乘向量求导推导
起因
我想玩RNN,但不知道如何对矩阵乘向量进行求导.
经过
推了一会,我会了.
设 A b = c Ab=c Ab=c
展开写 [ a 11 a 12 ⋯ a 1 n a 21 a 22 ⋯ a 2 n ⋮ ⋮ ⋱ ⋮ a n 1 a n 2 ⋯ a n n ] [ b 1 b 2 ⋮ b n ] = [ c 1 c 2 ⋮ c n ] \begin{bmatrix} a_{11}&a_{12}&\cdots&a_{1n}\\ a_{21}&a_{22}&\cdots&a_{2n}\\ \vdots&\vdots&\ddots&\vdots\\ a_{n1}&a_{n2}&\cdots&a_{nn} \end{bmatrix}\begin{bmatrix} b_1\\b_2\\\vdots\\b_n\end{bmatrix}=\begin{bmatrix} c_1\\c_2\\\vdots\\c_n\end{bmatrix} ⎣⎢⎢⎢⎡a11a21⋮an1a12a22⋮an2⋯⋯⋱⋯a1na2n⋮ann⎦