Editing Block matrix (section)

====Upper block triangular====
A matrix <math>A</math> is '''upper block triangular''' (or '''block upper triangular'''<ref name=":7">{{Cite book |last=Stewart |first=Gilbert W. |title=Matrix algorithms. 2: Eigensystems |date=2001 |publisher=Soc. for Industrial and Applied Mathematics |isbn=978-0-89871-503-3 |location=Philadelphia, Pa |pages=5}}</ref>) if

:<math>A = \begin{bmatrix}
A_{11} & A_{12} & \cdots & A_{1k} \\
0 & A_{22} & \cdots & A_{2k} \\
\vdots & \vdots & \ddots & \vdots \\
0 & 0 & \cdots & A_{kk}
\end{bmatrix}</math>,

where <math>A_{ij} \in \mathbb{F}^{n_i \times n_j}</math> for all <math>i, j = 1, \ldots, k</math>.<ref name=":5">{{Cite book |last=Bernstein |first=Dennis S. |title=Matrix mathematics: theory, facts, and formulas |publisher=Princeton University Press |year=2009 |isbn=978-0-691-14039-1 |edition=2 |location=Princeton, NJ |pages=168,298 |language=en}}</ref><ref name=":7" />