均值方差增量计算μ = ∑ i = 1 n x i n \mu = \frac{\sum_{i=1}^{n} x_i}{n} μ=n∑i=1nxi σ 2 = ∑ i = 1 n ( x i − μ ) 2 n = ∑ i = 1 n x i 2 − 2 ∑ i = 1 n x i μ + n μ 2 n = ∑ i = 1 n x i 2 − n μ 2 n = ∑ i = 1 n x i 2 n − μ 2 \begin{array}{ll} \sigma^2 &= \frac{\sum_{i=1}^{n}(x_i