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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