# JavaScript: Sum of the main diagonal elements of a square matrix

## JavaScript Math: Exercise-85 with Solution

Write a JavaScript program to compute the sum of the main diagonal elements of a square matrix.

In mathematics, a matrix (plural matrices) is a rectangular array or table of numbers, symbols, or expressions, arranged in rows and columns, which is used to represent a mathematical object or a property of such an object.

An m × n matrix: the m rows are horizontal and the n columns are vertical

In mathematics, a square matrix is a matrix with the same number of rows and columns. An n-by-n matrix is known as a square matrix of order n. Any two square matrices of the same order can be added and multiplied.

Example:

**Test Data:**

([ [1, 2, 3], [4, 5, 6], [7, 8, 9] ]) -> 15

( [ [-1, -2], [-4, -5] ]) -> -6

**Sample Solution:**

**JavaScript Code:**

```
/**
* Function to find the sum of the main diagonal elements of a square matrix.
* @param {number[][]} nums - The input square matrix.
* @returns {number} - The sum of the main diagonal elements.
*/
function test(nums) {
// Use reduce to sum the elements along the main diagonal of the matrix
return nums.reduce((x, y, i) => x + y[i], 0);
}
// Test cases
// Assign value to nums
nums = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
];
// Print the sum of the main diagonal elements of the said square matrix
console.log("Sum of the main diagonal elements of the said square matrix: " + test(nums));
// Repeat the above steps for a different value of nums
nums = [
[-1, -2],
[-4, -5]
];
console.log("Sum of the main diagonal elements of the said square matrix: " + test(nums));
```

Output:

Sum of the main diagonal elements of the said square matrix: 15 Sum of the main diagonal elements of the said square matrix: -6

**Flowchart: **

**Live Demo: **

See the Pen javascript-math-exercise-85 by w3resource (@w3resource) on CodePen.

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