Python Program to check if matrix is lower triangular

Given a square matrix and the task is to check the matrix is in lower triangular form or not. A square matrix is called lower triangular if all the entries above the main diagonal are zero. 

Examples:

Input : mat[4][4] = {{1, 0, 0, 0},
                     {1, 4, 0, 0},
                     {4, 6, 2, 0},
                     {0, 4, 7, 6}};
Output : Matrix is in lower triangular form.

Input : mat[4][4] = {{1, 0, 0, 0},
                     {4, 3, 0, 1},
                     {7, 9, 2, 0},
                     {8, 5, 3, 6}};
Output : Matrix is not in lower triangular form.

Python Program to check if matrix is lower triangular

Python3

# Python3 Program to check
# lower triangular matrix.

# Function to check matrix
# is in lower triangular
def islowertriangular(M):
    for i in range(0, len(M)):
        for j in range(i + 1, len(M)):
            if(M[i][j] != 0):
                    return False
    return True

# Driver function.
M = [[1,0,0,0],
     [1,4,0,0],
     [4,6,2,0],
     [0,4,7,6]]

if islowertriangular(M):
    print ("Yes")
else:
    print ("No")

# This code is contributed by Anurag Rawat

Output: 

Yes

Time Complexity: O(n²), where n represents the number of rows and columns of the given matrix.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

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