均方差，应该是 mmm 吧，怎能是 nnn 呢？应该把 σ=1n∑i=1n(xˉ−xi)2,xˉ=1n∑i=1nxi\sigma=\sqrt{\frac{1}{n}\sum\limits_{i=1}^{n}(\bar{x}-x_i)^2},\bar{x}=\frac{1}{n}\sum\limits_{i=1}^{n}x_iσ=n1i=1∑n(xˉ−xi)2,xˉ=n1i=1∑nxi，改成σ=1m∑i=1m(xˉ−xi)2,xˉ=1m∑i=1mxi\sigma=\sqrt{\frac{1}{m}\sum\limits_{i=1}^{m}(\bar{x}-x_i)^2},\bar{x}=\frac{1}{m}\sum\limits_{i=1}^{m}x_iσ=m1i=1∑m(xˉ−xi)2,xˉ=m1i=1∑mxi
