generated at
偏差積和

S_{xy}=\Sigma^n_{i=1}(x_i-\overline{x})(y_i-\overline{y})=\Sigma x_iy_i-\frac{(\Sigma x_i)(\Sigma y_i)}{n}.
y=xのときは、偏差平方和と呼ぶ

x_{i}-\overline{x}.