# Tabbing alignment and over-length sentence auto line break

【Question】When using "tabbing" under math mode with cases, how can I achieved the following at the same time:

(1) alignment in cases by "tabbing"

(2) over length element such as a long sentence in "tabbing" will automatically line break instead of going out of the page?

【Problematic CODE】

 \documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{tabularx}
\begin{document}

\begin{tabbing}
$\begin{cases} \= \text{trade}, \= p(\text{trade})=\dfrac{y}{v}, \= \text{when there is a long sentence in tabbing, it will break automatic instead of going out of the page}\\ \> \text{no trade}, \> p(\text{no trade})=1-\dfrac{y}{v} \end{cases}$
\end{tabbing}

\end{document}

• You can not nest display environments like cases across tabbing cells!" after you get ! Extra }, or forgotten \$. then any output that you may get from tex is entirely accidental and unplanned. Oct 11, 2015 at 20:28
• So manual indentation is the only way to achieve alignment in cases? Forget about cases, can tabbing achieve auto line break in math mode (text mode)? Oct 11, 2015 at 20:34
• Why do you want to use tabbing ? In over 25 years of latex use I have never seen occasion to use it. Oct 11, 2015 at 20:35
• Thought tabbing can achieve a more freely alignment. The spaces between cells in the first row tend to be affected easily by the elements put in the second row. Say if the element is a bit longer in the second row, it will increase the entire space between columns and the original spaces between adjacent cells in the first row will increase. Oct 11, 2015 at 20:43
• Howard just like tabular, it doesn't ever increase space between cells, it just enlarges all cells in a column to match the largest. It's almost always easier to use tabular. Oct 11, 2015 at 20:54

With tabbing you can't have automatic break of lines: you always have to specify a paragraph width for this (explicitly or computed).

Since this appears much like a math display, I suggest using cases alone:

\documentclass[12pt]{article}
\usepackage{amsmath}

\usepackage{lipsum} % for mock text

\begin{document}

\lipsum*[2]
$\begin{cases} \text{trade}, & p(\text{trade})=\dfrac{y}{v},\ % \parbox[t]{.6\displaywidth}{ when there is a long sentence in tabbing, it will break automatically instead of going out of the page } \\ \\[-1ex] \text{no trade}, & p(\text{no trade})=1-\dfrac{y}{v} \end{cases}$
\lipsum[3]

\end{document}


The empty line with a slight compensation is the simplest thing to move the two real lines far apart from each other.

The width 0.8\displaywidth is “eye computed”.

 \documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{array}
\begin{document}

\noindent X\dotfill X
$\left\{ \begin{tabular}{@{}l>l<>{\raggedright\arraybackslash}p{5cm}@{}} trade,& p(\text{trade})=\dfrac{y}{v},& \= when there is a long sentence in tabbing, it will break automatic instead of going out of the page\\ no trade,&p(\text{no trade})=1-\dfrac{y}{v} \end{tabular}\right.$

\end{document}