# Java Program to Display Lower Triangular Matrix

• Last Updated : 12 Jun, 2021

Lower Triangular Matrix is a square matrix in which all the elements above the principal diagonal are 0. If the matrix is not a square matrix, it can never be called the lower triangular matrix.

Examples

```Input 1: mat[][] = { {2, 1, 4},
{1, 2, 3},
{3, 6, 2}}

Output :  mat[][]= {{2, 0, 0},
{1, 2, 0},
{3, 6, 2}}

Explaination :    All the element below the principal diagonal needs to be 0.

Input 2 :  mat[][]=    {{4, 6},
{2, 8}}

Output :   mat[][]=     {{4, 0},
{2, 8}}

Input 3 :  mat[][] = { {2, 1, 4, 6},
{1, 2, 3, 7},
{3, 6, 2, 8} }

Output :   Matrix should be a Square Matrix```

Approach:

• If the matrix has equal rows and columns, continue the program else exit the program.
• Run the loop over the whole matrix, and for the rows, whose column number is greater than row number, make the element at that position equal to 0.

Below is the implementation of the above approach:

## Java

 `// Java program for displaying lower triangular matrix``import` `java.io.*;` `class` `GFG {``    ``static` `void` `lowerTriangularMatrix(``int` `matrix[][])``    ``{``        ``int` `row = matrix.length;``        ``int` `col = matrix[``0``].length;` `        ``// if number of rows and columns are not equal,``        ``// then return back``        ``if` `(row != col) {``            ``System.out.println(``                ``"Matrix should be a Square Matrix"``);``            ``return``;``        ``}``        ``else` `{``            ``// looping over the whole matrix``            ``for` `(``int` `i = ``0``; i < row; i++) {``                ``for` `(``int` `j = ``0``; j < col; j++) {` `                    ``// for the rows,whose column number is``                    ``// greater then row number,mark the``                    ``// element as 0``                    ``if` `(i < j) {``                        ``matrix[i][j] = ``0``;``                    ``}``                ``}``            ``}` `            ``System.out.println(``                ``"Lower Triangular Matrix is given by :-"``);``            ``// printing the lower triangular matrix``            ``for` `(``int` `i = ``0``; i < row; i++) {``                ``for` `(``int` `j = ``0``; j < col; j++) {``                    ``System.out.print(matrix[i][j] + ``" "``);``                ``}``                ``System.out.println();``            ``}``        ``}``    ``}``    ``public` `static` `void` `main(String[] args)``    ``{``        ``// driver code``        ``int` `mat[][]``            ``= { { ``2``, ``1``, ``4` `}, { ``1``, ``2``, ``3` `}, { ``3``, ``6``, ``2` `} };``        ``// calling the function``        ``lowerTriangularMatrix(mat);``    ``}``}`

Output:

```Lower Triangular Matrix is given by :-
2 0 0
1 2 0
3 6 2 ```
• Space Complexity: Matrix can be changed in-place. i.e no extra matrix space required.  0(N^2)
• Time Complexity: 0(N^2)

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