Diagonal Matrix

In linear algebra, a diagonal matrix is a matrix in which the entries outside the main diagonal are all zero; the term usually refers to square matrices. Elements of the main diagonal can either be zero or nonzero. An example of a 2×2 diagonal matrix is [ 3 0 0 2 ] {\displaystyle \left[{\begin{smallmatrix}3&0\\0&2\end{smallmatrix}}\right]} , while an example of a 3×3 diagonal matrix is [ 6 0 0 0 0 0 0 0 0 ] {\displaystyle \left[{\begin{smallmatrix}6&0&0\\0&0&0\\0&0&0\end{smallmatrix}}\right]} . An identity matrix of any size, or any multiple of it (a scalar matrix), is a diagonal matrix.