Java Program to find Sum of Diagonal Elements of a Matrix

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In the previous article, we have discussed Java Program to Find Sum of Matrix Elements

In this article we are going to see how we can write a program to calculate the sum of diagonal elements of a matrix in JAVA language.

Java Program to find Sum of Diagonal Elements of a Matrix

A 3*3 Matrix is having 3 rows and 3 columns where this 3*3 represents the dimension of the matrix. Means there are 3*3 i.e. total 9 elements in a 3*3 Matrix.

Let’s understand it in more simpler way.

                   | A00   A01   A02 |
Matrix A =  | A10   A11   A12 |
                   | A20   A21   A22 | 3*3
  • Matrix A represents a 3*3 matrix.
  • ‘A‘ represents the matrix element
  • ‘Aij‘ represents the matrix element at it’s matrix position/index.
  • ‘i‘ represents the row index
  • ‘j‘ represents the column index
  • Means A00=Aij  where i=0 and j=0,  A01=aij where i=0 and j=1 and like this.
  • Here we have started row value from 0 and column value from 0.

Let’s see different ways to find sum of diagonal elements of a 3*3 matrix.

Method-1: Java Program to find Sum of Diagonal Elements of a Matrix By Static Initialization of Array Elements

Approach:

  • Initialize an array of size 3×3 with values.
  • Show the array to the user.
  • Similarly use two for loops to iterate the rows and columns, then calculate the main diagonal sum.
  • Repeat the above step to calculate the counter diagonal sum.
  • Print the output.

Program:

import java.util.Scanner;

public class matrix
{
    public static void main(String args[])
    {
        //Scanner class to take input
        Scanner scan = new Scanner(System.in);

        // Initializing the 3X3 matrix i.e. 2D array
        int arr[][] = {{1,2,3},{4,5,6},{7,8,9}}, mainSum = 0, counterSum = 0;
        int row, col;
        
        System.out.print("Matrix : ");
        // Loop to print the elements
        for(row=0;row<3;row++)
        {
            // Used for formatting
            System.out.print("\n");
            for(col=0;col<3;col++)
            {
                System.out.print(arr[row][col]+" ");
            }
        }
        System.out.print("\n");
        // Loop to take the sum of main diagonal elements
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
            {
                if(row==col)
                    mainSum+=arr[row][col];
                // if(row+col==2)
            }
        System.out.println("The sum of main diagonal elements is : "+mainSum);

        // Loop to take the sum of counter diagonal elements
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
            {
                if(row+col==2)
                    counterSum+=arr[row][col];
            }
        System.out.println("The sum of counter diagonal elements is : "+counterSum);
    }
}


Output:

Matrix is : 
1 2 3 
4 5 6 
7 8 9 
The sum of main diagonal elements is : 15
The sum of counter diagonal elements is : 15

Method-2: Java Program to find Sum of Diagonal Elements of a Matrix By Dynamic Initialization of Array Elements

Approach:

  • Initialize an array of size 3×3.
  • Ask the user for input.
  • Use two for loops to iterate the rows and columns to input the array elements.
  • Show the array to the user.
  • Similarly use two for loops to iterate the rows and columns, then calculate the main diagonal sum.
  • Repeat the above step to calculate the counter diagonal sum.
  • Print the result.

Program:

import java.util.Scanner;

public class matrix
{
    public static void main(String args[])
    {
        //Scanner class to take input
        Scanner scan = new Scanner(System.in);

                // Initializing the 3X3 matrix i.e. 2D array
        int arr[][] = new int[3][3];

        System.out.println("Enter the 3x3 matrix elements :");
        int row, col, mainSum = 0, counterSum = 0;
        // Loop to take user input
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
                arr[row][col] = scan.nextInt();

        
        System.out.print("Matrix is : ");
        // Loop to print the elements
        for(row=0;row<3;row++)
        {
            // Used for formatting
            System.out.print("\n");
            for(col=0;col<3;col++)
            {
                System.out.print(arr[row][col]+" ");
            }
        }
        System.out.print("\n");
        // Loop to take the sum of main diagonal elements
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
            {
                if(row==col)
                    mainSum+=arr[row][col];
                // if(row+col==2)
            }
        System.out.println("The sum of main diagonal elements is : "+mainSum);

        // Loop to take the sum of counter diagonal elements
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
            {
                if(row+col==2)
                    counterSum+=arr[row][col];
            }
        System.out.println("The sum of counter diagonal elements is : "+counterSum);
    }
}


Output:

Enter the 3x3 matrix elements : 1 2 3 4 5 6 7 8 9
Matrix is : 
1 2 3 
4 5 6 
7 8 9 
The sum of main diagonal elements is : 15
The sum of counter diagonal elements is : 15

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