#algebra 

The **trace** of a **square [[Matrix|matrix]]** $\LARGE A$ is the sum of elements on the main diagonal of $\LARGE A$

Denoted as $\LARGE tr(A)=\displaystyle \sum^n_{i=1}a_{ii}$

На русском языке - след матрицы.

Russian notation:
$\LARGE sp(M)$ ("trace" in German)