第2章 线性代数

时间:2024-03-09 19:31:07
线性组合(linear combination)
A x = [ A 1 , 1 x 1 + A 1 , 2 x 2 + . . . A 1 , n x n A 2 , 1 x 1 + A 2 , 2 x 2 + . . . A 2 , n x n . . . A m , 1 x 1 + A m , 2 x 2 + . . . A m , n x n ] = x 1 [ A 1 , 1 A 2 , 1 . . . A m , 1 ] + x 2 [ A 1 , 2 A 2 , 2 . . . A m , 2 ] + . . . x n [ A 1 , n A 2 , n . . . A m , n ] = ∑ i = 1 n x i A : , i Ax = \begin{bmatrix} {A_{1,1}x_1 + A_{1, 2}x_2 + ... A_{1, n}x_n} \\ {A_{2,1}x_1 + A_{2, 2}x_2 + ... A_{2, n}x_n } \\ . \\ . \\ . \\ {A_{m,1}x_1 + A_{m, 2}x_2 + ... A_{m, n}x_n} \end{bmatrix} = x_1 \begin{bmatrix} A_{1,1} \\ A_{2,1}\\ . \\ . \\ . \\ A_{m,1} \end{bmatrix} + x_2 \begin{bmatrix} A_{1,2} \\ A_{2,2}\\ . \\ . \\ . \\ A_{m,2} \end{bmatrix} + ... x_n \begin{bmatrix} A_{1,n} \\ A_{2,n}\\ . \\ . \\ . \\ A_{m,n} \end{bmatrix} = \sum_{i=1}^{n} x_iA_{:, i} Ax= A1,1x1+A1,2x2+...A1,nxnA2,1x1+A2,2x2+...A2,nxn...Am,1x1+Am,2x2+...Am,nxn =x1 A1,1A2,1...Am,1 +x2 A1,2A2,2...Am,2 +...xn A1,nA2,n...Am,n =i=1nxiA:,i