The diagonal of a matrix refers to the elements that fall on a line drawn from the top left to the bottom right corner of the matrix. Diagonal elements of a matrix Aij consists of elements of that matrix where i = j. Here i and j are row and column indices respectively. This set of elements is also known as the main diagonal or principal diagonal elements.
Similarly, the elements that fall on a line drawn from the top right to the bottom left corner of a matrix are called antidiagonal or secondary diagonal elements.
For example, the main diagonal of matrix A contains elements 1, 5 and 9 and antidiagonal contains elements 3, 5 and 7.
Here is a C program to find the sum of diagonal elements of a matrix.
#include <stdio.h>
#define MAX 10
int main() {
int row, col;
int a[MAX][MAX];
int sum = 0;
// Read the matrix
printf("Enter number of rows and columns of the matrix: ");
scanf("%d%d", &row, &col);
printf("Enter elements of the matrix:\n");
for (int i = 0; i < row; i++)
for (int j = 0; j < col; j++)
scanf("%d", &a[i][j]);
// Calculate diagonal sum
for (int i = 0; i < row; i++)
for (int j = 0; j < col; j++)
if(i == j)
sum += a[i][j];
// Print result
printf("Sum of diagonal elements of the matrix is %d", sum);
return 0;
}
Output:
Enter number of rows and columns of the matrix: 3 3 Enter elements of the matrix: 1 5 6 3 4 2 2 1 5 Sum of diagonal elements of the matrix is 10
Sum of secondary diagonal elements
Here is a C program to find the sum of secondary diagonal or antidiagonal elements of an array.
#include <stdio.h>
#define MAX 10
int main() {
int row, col;
int a[MAX][MAX];
int sum = 0;
// Read the matrix
printf("Enter number of rows and columns of the matrix: ");
scanf("%d%d", &row, &col);
printf("Enter elements of the matrix:\n");
for (int i = 0; i < row; i++)
for (int j = 0; j < col; j++)
scanf("%d", &a[i][j]);
//Initialize the result matrix to 0
for (int i = 0; i < row; i++)
for (int j = 0; j < col; j++)
if(j == (col - (i + 1)))
sum += a[i][j];
// Print result matrix
printf("Sum of anti-diagonal elements of the matrix is %d", sum);
return 0;
}
Output:
Enter number of rows and columns of the matrix: 3 3 Enter elements of the matrix: 1 5 6 3 4 2 2 1 5 Sum of anti-diagonal elements of the matrix is 12
Feel free to post any questions you may have in the comments.
