\[\nabla_\mathbf{w}E(\mathbf{w})=\sum_{n=1}^N\{y(x_n,\mathbf{w})-t_n\}\phi(x_n)=0\]
\[\sum_{n=1}^N\phi^\text{T}(x_n)\mathbf{w}\phi(x_n)=\sum_{n=1}^Nt_n\phi(x_n)\]
\[\mathbf{w}\sum_{n=1}^N\phi(x_n)\phi^\text{T}(x_n) = \sum_{n=1}^Nt_n\phi(x_n)\]
原文：https://www.cnblogs.com/astoninfer/p/9253370.html