How to add the main diagonal of a python matrix?

Asked

Viewed 2,443 times

1

I am developing an algorithm and I want to know if there is a command to add the main diagonal of an array in Python

python

  • Not in Python, but it’s a trivial operation to implement. Why not try it yourself and post here if you can’t?

  • thanks, I’ve got it

2 answers

4

In Python there is no proper function for this, but implementing it is quite trivial.

A square matrix n x n can be represented as:

| (1, 1)   (1, 2)   (1, 3)   ...   (1, n) |
| (2, 1)   (2, 2)   (2, 3)   ...   (2, n) |
| (3, 1)   (3, 2)   (3, 3)   ...   (3, n) |
|  ...      ...      ...     ...    ...   |
| (n, 1)   (n, 2)   (n, 3)   ...   (n, n) |

Where the main diagonal is composed of: (1, 1), (2, 2), (3, 3), ..., (n, n); that is, all values in position (i, j) where i = j.

So, as the index in Python starts at 0, you need to go from 0 to n-1, n being the size of the matrix.

def soma_diagonal_principal(matriz):
    n = len(matriz)
    assert n == len(matriz[0]), 'Matriz precisa ser quadrada'
    return sum(matriz[i][i] for i in range(n))

The assert in the function will ensure that the matrix is square.

The Numpy library has the function numpy.trace that returns the diagonal sum.

  • thank you.......

3

n= 4

m= [[2,6,4,3],[2,4,6,4],[5,1,0,4],[4,5,4,6]]

sum_diagonal = sum(m[i][i]for i in range(n))

print(sum_diagonal)

Browser other questions tagged python

You are not signed in. Login or sign up in order to post.