Diagonal matrix

A diagonal matrix is a square matrix all of whose nonzero entries are along the main diagonal. Examples include the identity matrix, the zero matrix, and the matrix: <math> \left(\begin{matrix} 1 &0 &0\\ 0 &2 &0\\ 0 &0 &3\end{matrix}\right) </math>

The eigenvalues of a diagonal are the non-zero elements.

This is a special case of a Triangular matrix.