# Two column equation block with vertical separator

I have seen various examples in text books and web pages (like here) of two column equation blocks, where the left column has some equation(s) and the right column has some explanation on variable meanings and/or other things. I wish to split an equation like below into two columns with a vertical separator in between without involving minipage, Tikz, and other fancy stuff like that. Seems like something that should be in common demand. But I cannot find an example of it. Any help would be greatly appreciated.

\begin{flalign}
z &= \frac{R\left(S_2 − S_1\right)}{2\left(S_1 + S_2\right)} + \frac{R}{2}\\
text{\scriptsize{where}}
&\text{\scriptsize{ $R$ is the camera range,}} \nonumber\\
&\text{\scriptsize{$S_1$ is the amount of the light pulse received, and}} \nonumber\\
&\text{\scriptsize{$S_2$ is the amount of the light pulse blocked \cite{medina1992three} \nonumber.
}}
\end{flalign}


I am using the scrbook documentclass.

You can use a | delimiter and an array

% arara: pdflatex

\documentclass{scrbook}
\usepackage{blindtext}
\usepackage{mathtools}
\usepackage{array}

\begin{document}
\blindtext
\begin{equation}
z = \frac{R(S_2 − S_1)}{2(S_1 + S_2)} + \frac{R}{2} \quad \left|\quad\begin{array}{r@{\ }>$l<$}
R   & is the amount of the light pulse received, and\\
S_1 & is the amount of the light pulse received, and\\
S_2 & is the amount of the light pulse blocked [MED92]\\
\end{array}\right.
\end{equation}
\begin{equation}
z = \frac{R(S_2 − S_1)}{2(S_1 + S_2)} + \frac{R}{2} \quad \left|\quad\begin{array}{>$l<$}
$R$ is the amount of the light pulse received, and\\
$S_1$ is the amount of the light pulse received, and\\
$S_2$ is the amount of the light pulse blocked [MED92]\\
\end{array}\right.
\end{equation}
\blindtext
\end{document} • Thanks for the input! Actually, I wanted to have the text side-by-side with the equation, and the visible vertical line between the equation and the text, not between the 'where' and the rest of the text :) – Subhamoy S. Nov 3 '14 at 15:27
• That indeed does it! Thank you very much! I wish there were a less hackish way, but this works too! – Subhamoy S. Nov 3 '14 at 15:40
• @SubhamoySengupta Then you will like my completely revised answer. I got your question wrong in the first case. – LaRiFaRi Nov 3 '14 at 15:50
• May I request one small modification? What would happen if there are 2 subequations? – Subhamoy S. Nov 3 '14 at 19:55