# vertical and horizontal equations

I want to write an equation like this (pic related).

What a good way to achieve it in LaTeX?

edit: I'm referring to the vertical math relation and alignment, not to how to get the norms, the boldsymbols or the coloneqq/eqqcolon.

## 1 Answer

Here's a solution that employs the mathtools, bm, and graphicx packages, with an embedded array environment to house the vertical subcomponent.

\documentclass{article}
\usepackage{mathtools} % for '\coloneqq' and '\DeclarePairedDelimiter' macros
\usepackage{bm}        % for '\bm' macro
\usepackage{graphicx}  % for ' \rotatebox' macro

\DeclarePairedDelimiter{\norm}{\lVert}{\rVert}
\newcommand{\rotcoloneqq}{\rotatebox[origin=c]{90}{$\coloneqq$}}

\begin{document}
$k_0 \coloneqq \norm{\bm{k}_0} = \begin{array}[t]{@{}c@{}} \norm{\bm{k}} \\ \rotcoloneqq \\ k \end{array} =\frac{2\pi}{\lambda}$

\end{document}
• I prefer this answer, over @campa's because it can be generalized to arbitrarily many trees of equations without much effort. However, thank you both. – ɪdɪət strəʊlə Aug 22 '17 at 15:04