Upper Triangular Matrix/Examples/m less than n

Example of Upper Triangular Matrix

An upper triangular matrix of order $m \times n$ such that $m < n$:

$\mathbf U = \begin{bmatrix}

a_{11} & a_{12} & a_{13} & \cdots & a_{1, m - 1} & a_{1m} & \cdots & a_{1, n - 1} & a_{1n} \\

    0 & a_{22} & a_{23} & \cdots &     a_{2, m - 1} &       a_{2m} & \cdots &     a_{2, n - 1} &      a_{2n} \\
    0 &      0 & a_{33} & \cdots &     a_{3, m - 1} &       a_{3m} & \cdots &     a_{3, n - 1} &      a_{3n} \\

\vdots & \vdots & \vdots & \ddots & \vdots & \vdots & \ddots & \vdots & \vdots \\

    0 &      0 &      0 & \cdots & a_{m - 1, m - 1} & a_{m - 1, m} & \cdots & a_{m - 1, n - 1} & a_{m - 1, n} \\
    0 &      0 &      0 & \cdots &                0 &       a_{mm} & \cdots &     a_{m, n - 1} &       a_{mn} \\

\end{bmatrix}$