Trace

The trace of a matrix is simply the sum of all value in the diagonal of the matric. Mathematically, it is represented as:

$$tr(A) = \sum_{i}^n a_{i,i}$$

Example:

$$ A = \begin{pmatrix} 2 & 1 \\ 4 & 3 \\ 3 & 2 \end{pmatrix}$$

then:

$$ tr(A) = 2 + 3 = 5 $$

Implementation in Numpy

import numpy as np

A = np.array([2,1,4,3,3,2]).reshape(3,2)
A

array([[2, 1], [4, 3], [3, 2]])

np.trace(A)

5