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Java Program to Check Whether a Given Matrix is Lower Triangular Matrix or Not
• Last Updated : 07 Jan, 2021

In the lower triangular matrix, the elements that are present above the diagonal should be 0. Given a matrix and the task is to check the matrix is in lower triangular form or not. A matrix must be a square matrix. A square matrix is called lower triangular if all the entries above the main diagonal are zero.

Example –

```Input:
1    0    0
1    2    0
1    2    3

Output: Matrix is lower triangular matrix

Input:
1    2    2
2    1    1
2    2    2

Output: Matrix is not a lower triangular matrix```

Approach:

1. Check if the given matrix is square or not.
2. If yes, then traverse the upper triangle part matrix.
3. Check if all the entries above the main diagonal are zero.
4. If yes, then print Matrix is a lower triangular matrix.

Below is the implementation of the above approach:

## Java

 `// Java Program to check for``// a lower triangular matrix.`` ` `import` `java.util.Scanner;`` ` `public` `class` `LowerTriangularMatrix {``    ``public` `static` `boolean``    ``isLowerTriangularMatrix(``int``[][] matrix)``    ``{``        ``for` `(``int` `i = ``0``; i < matrix[``0``].length; i++) {``            ``for` `(``int` `j = i + ``1``; j < matrix[``0``].length; j++) {``                ``if` `(matrix[i][j] != ``0``)``                    ``return` `false``;``            ``}``        ``}``        ``return` `true``;``    ``}``    ``public` `static` `void` `main(String args[])``    ``{``        ``int` `rows = ``3``, columns = ``3``;`` ` `        ``// returns true if number of rows and columns are``        ``// equal else false``        ``if` `(rows == columns) {``            ``// initializing the matrix``            ``int` `Matrix[][]``                ``= { { ``1``, ``0``, ``0` `}, { ``2``, ``3``, ``0` `}, { ``5``, ``6``, ``7` `} };`` ` `            ``// Display the values of matrix``            ``System.out.println(``"Matrix is : "``);``            ``for` `(``int` `i = ``0``; i < rows; i++) {``                ``for` `(``int` `j = ``0``; j < columns; j++) {``                    ``System.out.print(Matrix[i][j] + ``"\t"``);``                ``}``                ``System.out.println();``            ``}`` ` `            ``// Function call``            ``boolean` `result``                ``= isLowerTriangularMatrix(Matrix);`` ` `            ``// returns true if matrix is lower triangular``            ``// matrix else false``            ``if` `(result == ``true``) {``                ``System.out.println(``                    ``"Matrix is lower triangular matrix"``);``            ``}``            ``else` `{``                ``System.out.println(``                    ``"Matrix is not lower triangular matrix"``);``            ``}``        ``}``        ``else` `{``            ``System.out.println(``                ``"Number of rows and number of columns should be equal"``);``        ``}``    ``}``}`
Output
```Matrix is :
1    0    0
2    3    0
5    6    7
Matrix is lower triangular matrix
```

Time Complexity: O(N2), where N is the length of the row in a square matrix.

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