A square matrix in which all the elements outside the main diagonal are zero.
The elements of the diagonal are the elements whose indices are equal : \(a_{1,1},\space a_{2,2},\space a_{3,3},\space …\).
Examples
\(\begin{pmatrix}2 & 0 & 0\\0 & –5 & 0\\0 &0 & –7\end{pmatrix}\) , \(\begin{pmatrix}2 & 0 & 0\\0 & 0 & 0\\0 &0 & –7\end{pmatrix}\) , \(\begin{pmatrix}2 & 0\\0 & –5\end{pmatrix}\)