我想使用二維數組找到方差和標准差。 我做了這個程序，但是 output 來的不正確

Question

我想使用 2D 數組找到方差和標准差我做了這個程序，但是 output 通信不正確。 請幫助我應該做什么/修改它以獲得所需的 output。

輸入

3 4

1 0 1 1 1 1 1 1 1 1 1 1

解決方案 output

0.07513148009038192

0.27410122234383033

預期 output

0.0764

0.2764

我的程序：

import java.util.*;
import java.text.DecimalFormat;

public class Source {
   public static void main(String[] args) {
       Scanner s = new Scanner(System.in);
       int n = s.nextInt();
       int m = s.nextInt();
       int[][] arr = new int[n][m];
       for (int i = 0; i < n; i++)
           for (int j = 0; j < m; j++)
               arr[i][j] = s.nextInt();
       varianceAndStandardDeviation(arr, n, m);
   }

   // Method for calculating variance
   static void varianceAndStandardDeviation(int arr[][], int n, int m) {
       // Write your code here
       double[][] diff = new double[n][m];
       double avg = 0f;
       double var = 0f;
       double std_dev = 0f;
       for (int i = 0; i < n; i++)
           for (int j = 0; j < m; j++)
           {
               avg = (avg + arr[i][j]);
               avg = avg/(n*m);
               diff[i][j] = (avg - arr[i][j]);
               var = ((diff[i][j] * diff[i][j])/((n*m)-1));
               std_dev = Math.pow(var, 0.5);
           }
           System.out.println(var);
           System.out.println(std_dev);
   }
}

Answer 1

https://www.geeksforgeeks.org/variance-standard-deviation-matrix/你有完整的教程。

Answer 2

進行 2 次傳遞：一次計算平均值，另一次計算方差：

import java.util.Scanner;

public class Source {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int n = s.nextInt();
        int m = s.nextInt();
        int[][] arr = new int[n][m];
        for (int i = 0; i < n; i++)
            for (int j = 0; j < m; j++)
                arr[i][j] = s.nextInt();
        varianceAndStandardDeviation(arr, n, m);
    }

    // Method for calculating variance
    static void varianceAndStandardDeviation(int arr[][], int n, int m) {
        double avg = 0;
        double variance = 0;
        for (int i = 0; i < n; i++)
            for (int j = 0; j < m; j++)
                avg += arr[i][j];
        avg /= n * m;
        for (int i = 0; i < n; i++)
            for (int j = 0; j < m; j++)
                variance += Math.pow((arr[i][j] - avg), 2);
        variance /= n * m;

        System.out.printf("%.4f%n", variance);
        System.out.printf("%.4f%n", Math.sqrt(variance));
    }
}