Program to print Lower triangular and Upper triangular matrix of an array

Prerequisite – Multidimensional Arrays in C / C++

Given a two dimensional array, Write a program to print lower triangular matrix and upper triangular matrix.

  • Lower triangular matrix is a matrix which contain elements below principle diagonal including principle diagonal elements and rest of the elements are 0.
  • Upper triangular matrix is a matrix which contain elements above principle diagonal including principle diagonal elements and rest of the elements are 0.

Examples:

Input : matrix[3][3] = {1 2 3
                       4 5 6
                       7 8 9}
Output :
Lower : 1 0 0        Upper : 1 2 3
        4 5 0                0 5 6
        7 8 9                0 0 9

Input : matrix[3][3] = {7 8 9
                        3 2 1
                        6 5 4}
Output :
Lower : 7 0 0       Upper : 7 8 9
        3 2 0               0 2 1
        6 5 4               0 0 4

Steps:

  1. For lower triangular matrix, we check the index position i and j i.e row and column respectively. If column position is greater than row position we simply make that position 0.
  2. For upper triangular matrix, we check the index position i and j i.e row and column respectively. If column position is smaller than row position we simply make that position 0.

C++

// CPP program to print Lower 
// triangular and Upper triangular
// matrix of an array
#include<iostream>

using namespace std;

// Function to form lower triangular matrix
void lower(int matrix[3][3], int row, int col)
{
	int i, j;
	for (i=0; i<row; i++)
	{
		for (j=0; j<col; j++)
		{
			if (i<j)
			{
				matrix[i][j] = 0;
			}
			cout << matrix[i][j] << " ";
		}
		cout << endl;
	}
}

// Function to form upper triangular marix
void upper(int matrix[3][3], int row, int col)
{
	int i, j;
	
	for (i=0; i<row; i++)
	{
		for (j=0; j<col; j++)
		{
			if (i>j)
			{
				matrix[i][j] = 0;
			}
			cout << matrix[i][j] << " ";
		}
		cout << endl;
	}
}

// Driver function
int main()
{
	int matrix[3][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
	int row = 3, col = 3;
	
	cout << "Lower triangular matrix: \n";
	lower(matrix, row, col);
	
	cout << "Upper triangular matrix: \n";
	upper(matrix, row, col);
		
	return 0;
}

Java

// Java program to print Lower 
// triangular and Upper triangular
// matrix of an array

class Test
{
	// method to form lower triangular matrix
	static void lower(int matrix[][], int row, int col)
	{
	    int i, j;
	    for (i=0; i<row; i++)
	    {
	        for (j=0; j<col; j++)
	        {
	            if (i<j)
	            {
	                matrix[i][j] = 0;
	            }
	            System.out.print(matrix[i][j] + " ");
	        }
	        System.out.println();
	    }
	}
	 
	// Method to form upper triangular matrix
	static void upper(int matrix[][], int row, int col)
	{
	    int i, j;
	     
	    for (i=0; i<row; i++)
	    {
	        for (j=0; j<col; j++)
	        {
	            if (i>j)
	            {
	                matrix[i][j] = 0;
	            }
	            System.out.print(matrix[i][j] + " ");
	        }
	        System.out.println();
	    }
	}
	
	// Driver method
	public static void main(String args[])
	{
		int matrix[][] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
	    int row = 3, col = 3;
	     
	    System.out.println("Lower triangular matrix: ");
	    lower(matrix, row, col);
	     
	    System.out.println("Upper triangular matrix: ");
	    upper(matrix, row, col);
	}
}


Output:
Lower triangular matrix: 
1 0 0 
4 5 0 
7 8 9 
Upper triangular matrix: 
1 0 0 
0 5 0 
0 0 9 

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