# 程序检查矩阵是否为下三角 > 原文： [https://www.geeksforgeeks.org/program-check-matrix-lower-triangular/](https://www.geeksforgeeks.org/program-check-matrix-lower-triangular/) 给定一个正方形矩阵，任务是检查矩阵是否为下三角形式。 如果主对角线上的所有条目均为零，则将方阵称为下三角。  示例： ``` 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. ``` ## C++ ```cpp // Program to check lower // triangular matrix. #include <bits/stdc++.h> #define N 4 using namespace std; // Function to check matrix is in  // lower triangular form or not. bool isLowerTriangularMatrix(int mat[N][N]) {     for (int i = 0; i < N; i++)         for (int j = i + 1; j < N; j++)             if (mat[i][j] != 0)                 return false;     return true; } // Driver function. int main() {     int mat[N][N] = { { 1, 0, 0, 0 },                       { 1, 4, 0, 0 },                       { 4, 6, 2, 0 },                       { 0, 4, 7, 6 } };     // Function call     if (isLowerTriangularMatrix(mat))         cout << "Yes";     else         cout << "No";     return 0; } ``` ## Java ```java // Java Program to check for  // a lower triangular matrix. import java.io.*; class Lower_triangular {     int N = 4;     // Function to check matrix is      // in lower triangular form or not.     boolean isLowerTriangularMatrix(int mat[][])     {         for (int i = 0; i < N; i++)             for (int j = i + 1; j < N; j++)                 if (mat[i][j] != 0)                     return false;         return true;     }     // Driver function.     public static void main(String args[])     {         Lower_triangular ob = new Lower_triangular();         int mat[][] = { { 1, 0, 0, 0 },                         { 1, 4, 0, 0 },                         { 4, 6, 2, 0 },                         { 0, 4, 7, 6 } };         // Function call         if (ob.isLowerTriangularMatrix(mat))             System.out.println("Yes");         else             System.out.println("No");     } } // This code is contributed by Anshika Goyal. ``` ## Python3 ```py # 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 ``` ## C# ```cs // C# program to check for // a lower triangular matrix. using System; class Lower_triangular  {     int N = 4;     // Function to check matrix is     // in lower triangular form or not.     bool isLowerTriangularMatrix(int[, ] mat)     {         for (int i = 0; i < N; i++)             for (int j = i + 1; j < N; j++)                 if (mat[i, j] != 0)                     return false;         return true;     }     // Driver function.     public static void Main()     {         Lower_triangular ob = new Lower_triangular();         int[, ] mat = { { 1, 0, 0, 0 },                         { 1, 4, 0, 0 },                         { 4, 6, 2, 0 },                         { 0, 4, 7, 6 } };         // Function call         if (ob.isLowerTriangularMatrix(mat))             Console.WriteLine("Yes");         else             Console.WriteLine("No");     } } // This code is contributed by vt_m. ``` ## PHP ```php <?php // PHP Program to check lower // triangular matrix. $N = 4; // Function to check matrix is in  // lower triangular form or not. function isLowerTriangularMatrix($mat) {     global $N;     for ($i = 0; $i < $N; $i++)         for ($j = $i + 1; $j < $N; $j++)             if ($mat[$i][$j] != 0)                 return false;     return true; } // Driver Code $mat = array(array( 1, 0, 0, 0 ),              array( 1, 4, 0, 0 ),              array( 4, 6, 2, 0 ),              array( 0, 4, 7, 6 ));  // Function call if (isLowerTriangularMatrix($mat))     echo("Yes"); else     echo("No"); // This code is contributed by Ajit. ?> ``` Output: ``` Yes ``` * * * * * *