K-means
組內變異
$$\begin{aligned} \operatorname{W}(C_k)&:=\frac{1}{|C_k|}\sum_{i,i'\in{C_k}}\operatorname{D_{Euclidean}^2}(x_i,x_{i'}) \\ &=\frac{1}{n_{c_k}}\sum_{i,i'\in{C_k}}\sum_{j=1}^p(x_{i,j}-x_{i',j})^2 \\ &=2\times\sum_{i}^N\sum_{j=1}^p(x_{i,j}-\...
