Matrix has a special function called trace function. If is a square matrix then the sum of its main diagonal entry is called trace of matrix
and is denoted by
.
Let be a square matrix with size
, then
The trace of matrix is

Let is see few examples of traces of matrices.
Example #1
Let A be a square matrix of size
The trace of matrix is

Example #2
Let B be a square matrix of size
The trace of matrix is

If the matrix A is not a square matrix, then is not defined.