Definition:Triangular Matrix/Upper Triangular Matrix

Definition
An upper triangular matrix is a square matrix in which all the elements below the diagonal are zero.

That is, all the non-zero elements are in the upper triangle:


 * $\mathbf U = \begin{bmatrix}

a_{11} & a_{12} & a_{13} & \cdots & a_{1,n-1} & a_{1n} \\ 0 & a_{22} & a_{23} & \cdots & a_{2,n-1} & a_{2n} \\ 0 & 0 & a_{33} & \cdots & a_{3,n-1} & a_{3n} \\ \vdots & \vdots & \vdots & \ddots & \vdots & \vdots \\ 0 & 0 & 0 & \cdots & a_{n-1,n-1} & a_{n-1,n} \\ 0 & 0 & 0 & \cdots & 0 & a_{nn} \\ \end{bmatrix}$

That is, $\mathbf U$ is upper triangular iff:
 * $\forall a_{ij} \in \mathbf U: i > j \implies a_{ij} = 0$