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计算双数组的协方差。
//package com.nowjava; public class Main {//n o w j a v a . c o m - 时 代 Java 提 供 public static void main(String[] argv) throws Exception { double[] v1 = new double[] { 34.45, 35.45, 36.67, 37.78, 37.0000, 37.1234, 67.2344, 68.34534, 69.87700 }; double[] v2 = new double[] { 34.45, 35.45, 36.67, 37.78, 37.0000, 37.1234, 67.2344, 68.34534, 69.87700 }; System.out.println(covariance(v1, v2)); } /** * Computes the covariance. */ public static double covariance(double[] v1, double[] v2) { if (v1.length != v2.length) throw new IllegalArgumentException( "Arrays must have the same length : " + v1.length + ", " + v2.length); final double m1 = mean(v1); final double m2 = mean(v2); /** * 时 代 J a v a - nowjava.com 提 供 **/ double ans = 0.0; for (int i = 0; i < v1.length; i++) ans += (v1[i] - m1) * (v2[i] - m2); return ans / (v1.length - 1); } /** * Computes the covariance. */ public static double covariance(int[] v1, int[] v2) { if (v1.length != v2.length) throw new IllegalArgumentException( "Arrays must have the same length : " + v1.length + ", " + v2.length); final double m1 = mean(v1); final double m2 = mean(v2); double ans = 0.0; for (int i = 0; i < v1.length; i++) ans += (v1[i] - m1) * (v2[i] - m2); return ans / (v1.length - 1); } /** * 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 m