In linear algebra, the main diagonal of a square matrix is the diagonal which runs from the top left corner to the bottom right corner. For example, the following matrix has 1s down its main diagonal:

$\backslash begin\{bmatrix\}$

1 & 0 & 0\\ 0 & 1 & 0\\ 0 & 0 & 1\end{bmatrix}

A square matrix like the above in which the entries outside the main diagonal are all zero is called a diagonal matrix. The sum of the entries on the main diagonal of a matrix is known as the trace of that matrix.

Linear algebra

Diagonal principal | Diagonale (Lineare Algebra) | Diagonal principal | Diagonale principale | Diagonale principale | אלכסון ראשי | Hoofddiagonaal | Przekątna główna macierzy