Question

矩阵乘法题列矩阵X=(x1……xn) 满足 x^Tx=1 设 H=E-2XX^T 则 H*H=?

Answer 1

H*H 是 H^2 吧.

H^2 = (E-2XX^T)(E-2XX^T)

= E -4XX^T + 4 X(X^TX)X^T

= E -4XX^T + 4 XX^T

= E.