Compute Principal Diagonal Sum of a Javascript Matrix (Node)

Question

I’m trying to calculate the main diagonal of an array in Js, someone could help ?

function calcularDiagonal(matriz) {
  let soma = 0;
  for(let i = 0; i < matriz.length; i++) {
    for(let j = 0; j < matriz.length; j++) {
      if( matriz[i] == matriz[j]) {
        soma += matriz[i];
      }
    }
  }
  return soma;
}

const matriz = [[1,2,3,4,4,4,5,5,5]];

console.log(calcularDiagonal(matriz));

I did so but is returning a wrong result, which is :

01,2,3,4,4,4,5,5,5

But it should give the result 10, if anyone can see what’s wrong, thank you.

Answer 1

It seems that lack concept, then: Square matrix is a special type of matrix that has the same number of rows and the same number of columns, and every square matrix has two diagonals: Main Diagonal and Secondary Diagonal, example:

and its main diagonal is: a11 = 12, a22 = 6, a33 = 0 e a44 = 15.

Computationally an example of code:

const matriz = [
  [12,-8,15,6],
  [1,6,20,-9],
  [0,-4,0,-8],
  [-1,6,0,15]
];

function calculo(matriz) {
  const count = matriz.length;
  let result = 0;
  for(let i = 0; i < count; i++) {
    result += matriz[i][i];
  }
  return result;
}

console.log(calculo(matriz));

<table border="1" width="100%">
  <tr>
    <td>12</td>
    <td>-8</td>
    <td>15</td>
    <td>6</td>
  </tr>
  <tr>
    <td>1</td>
    <td>6</td>
    <td>20</td>
    <td>-9</td>
  </tr>
  <tr>
    <td>0</td>
    <td>-4</td>
    <td>0</td>
    <td>-8</td>
  </tr>
  <tr>
    <td>-1</td>
    <td>6</td>
    <td>0</td>
    <td>15</td>
  </tr>
</table>

Its main diagonal are the numbers 12, 6, 0, 15 respectively the positions 1,1 - 2,2 - 3,3 and 4,4 is sum is 33 as demonstrated in the code this sum only happens in quadratic matrix, that is, the same number of rows is equal to the same number of columns and vice versa (3x3, 4x4, etc);