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计算（经偏差校正的样本）方差。
//package com.nowjava;/*from n o w j a v a . c o m*/ public class Main { public static void main(String[] argv) throws Exception { double[] v = new double[] { 34.45, 35.45, 36.67, 37.78, 37.0000, 37.1234, 67.2344, 68.34534, 69.87700 }; System.out.println(variance(v)); } /** * Computes the (bias-corrected sample) variance. */ public static double variance(double[] v) { if (v.length > 1) { final double m = mean(v);//N o w J a v a . c o m 提 供 double ans = 0.0; for (int i = 0; i < v.length; i++) ans += (v[i] - m) * (v[i] - m); return ans / (v.length - 1); } else throw new IllegalArgumentException( "Array length must be of 2 or greater."); } /** * Computes the (bias-corrected sample) variance. */ public static double variance(int[] v) { if (v.length > 1) { final double m = mean(v); double ans = 0.0; for (int i = 0; i < v.length; i++) ans += (v[i] - m) * (v[i] - m); return ans / (v.length - 1); } else throw new IllegalArgumentException( "Array length must be of 2 or greater."); } /** * Computes the mean. */ public static double mean(double[] v) { if (v.length == 0) throw new IllegalArgumentException( "Nothing to compute! The array must have at least one element."); return (mass(v) / (double) v.length); } /** * Computes the mean. */ public static double mean(int[] v) { if (v.length == 0) throw new IllegalArgumentException( "Nothing to compute! The array must have at least one element."); return (mass(v) / (double) v.length); } /** * Returns the sum of the elements of the array. */ public static double mass(double[] v) {