Java Program to Display Lower Triangular Matrix

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In the previous article, we have discussed Java Program to Check Whether Two Matrices are Equal or Not

In this article we are going to see how we can write a program to display the lower triangular matrix in JAVA language.

Java Program to Display Lower Triangular 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.

Lower triangular matrix is a square matrix in which Aij elements are 0 i.e Aij=0 for j>i means all elements above the main diagonal are zero.

                                           1  0  0
Lower Triangular Matrix=   7  4  0
                                           8  9  3

Let’s see different ways to Display Lower Triangular Matrix.

Method-1: Java Program to Display Lower Triangular Matrix By Static Initialization of Array Elements

Approach:

  • Declare two arrays of size 3×3, one with elements.
  • Use two for loops to iterate the rows and columns .
  • Inside the for loops for all col>row locations store a zero, else copy the elements from the main array to the resultant array.
  • Print the resultant array.

Program:

public class matrix{
    public static void main(String args[])
    {

        // Initializing the 3X3 matrix i.e. 2D array
        int arr[][] = {{9,2,2},{4,4,2},{7,2,6}}, res[][] = new int[3][3];
        int row, col ;
        
        System.out.print("The matrix elements are : ");
        printMatrix(arr);

        // Loops to store the lower triangular matrix 
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
            {   
                if(row<col)
                    res[row][col]=0;
                else
                    res[row][col]= arr[row][col];
            }   
        System.out.print("\n\nThe lower triangular matrix : ");
        printMatrix(res);
    }

    // Method to print the matrix
    static void printMatrix(int arr[][])
    {
        int row, col;
        // 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]+" ");
            }
        }
    }
}



Output:

The matrix elements are : 
9 2 2 
4 4 2 
7 2 6

The lower triangular matrix : 
9 0 0 
4 4 0 
7 2 6

Method-2: Java Program to Display Lower Triangular Matrix By Dynamic Initialization of Array Elements

Approach:

  • Initialize two arrays of size 3×3.
  • Ask the user for input of array elements and store them in the one array using two for loops.
  • Use two for loops to iterate the rows and columns .
  • Inside the for loops for all col>row locations store a zero, else copy the elements from the main array to the resultant array.
  • Print the resultant array.

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], res[][] = new int[3][3];
        int row, col ;
        
        // Taking matrix1 input
        System.out.println("\nEnter matrix elements : ");
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
                arr[row][col] = scan.nextInt();
        
        System.out.print("The matrix elements are : ");
        printMatrix(arr);

        // Loops to store the lower triangular matrix
        for(row=0;row<3;row++)
            for(col=0;col<3;col++)
            {   
                if(row<col)
                    res[row][col]=0;
                else
                    res[row][col]= arr[row][col];
            }   
        System.out.print("\n\nThe lower triangular matrix : ");
        printMatrix(res);
    }

    // Method to print the matrix
    static void printMatrix(int arr[][])
    {
        int row, col;
        // 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]+" ");
            }
        }
    }
}


Output:

Enter matrix elements : 1 2 3 1 2 1 3 4 5 6
The matrix elements are : 
1 2 3 
1 2 1 
3 4 5

The lower triangular matrix : 
1 0 0 
1 2 0 
3 4 5

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