# How can I break a long equation?

Upon compiling, one of my equations extends out of my column width in my final output. Options I tried--

1. breqn package asks for expl3.sty file which the compiler is unable to locate, (would have been the easiest way in the {dmath} environment
2. // in the equation,
3. {split}, {multiline} environment of amsmath but none of the 3 approaches seem to work.

PS: I use latest version of TexnicCenter (+MikTeX 2.9) and the equation is in the {equation} environment right now.

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MikTeX should automatically install expl3. If not, you can always add it via its package manager. –  Caramdir Aug 6 '11 at 17:09
TeXnicCenter (TXC) has difficulties with automatic package installation. See MiKTeX 2.9 Issues for the details and a possible remedy. –  Thorsten Donig Aug 6 '11 at 17:12
I find it odd that // did not work. Are you perhaps using  for this equation in which case you can't use //? –  Peter Grill Aug 6 '11 at 17:26
maybe it is because the correct syntax is \\ ? –  percusse Aug 13 '11 at 19:21

none of the 3 approaches seem to work

That is a bad sentence. Do you get any errors?

Here is an example of the documentation of amsmath with split

\documentclass{article}
\usepackage{amsmath}
\begin{document}

$$\label{e:barwq} \begin{split} H_c&=\frac{1}{2n} \sum^n_{l=0}(-1)^{l}(n-{l})^{p-2} \sum_{l _1+\dots+ l _p=l}\prod^p_{i=1} \binom{n_i}{l _i}\\ &\quad\cdot[(n-l )-(n_i-l _i)]^{n_i-l _i}\cdot \Bigl[(n-l )^2-\sum^p_{j=1}(n_i-l _i)^2\Bigr]. \end{split}$$

\end{document}

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Thanks everyone,have been struggling with it for almost 2 days now, but no success yet. Here are the results of your kind suggestions:@caramdir The pckge mgr shws an eror whle installing expl3 "Unknown archive file size", @Thorsten I am afraid I do not see how to change "MikTex Options",@Peter Yup, // doesn't work, could you pls explain what do you mean by...[ ] for this equation...?@Werner The problem/error I face when I use split is that no pdf output is created. Also for some mysterious reason my error output window has disappeared and can't get it via tools>wind>cmpl reslt. Cheers –  Abhimanyu Arora Aug 6 '11 at 23:18
@Thorsten posted a comment about "Unknown archive file size" of the expl3 package update using MiKTeX Package Manager suggesting that you Syncronize your repository. See/try his answer at the bottom of the link provided. –  Werner Aug 6 '11 at 23:51
@Abhimanyu: Did you include the amsmath package (for split, etc.)? –  Caramdir Aug 7 '11 at 2:55
Is there any way to put the reference number at the bottom of the equation? –  Mohammad Aliannejadi Oct 4 '13 at 9:52
@MOLi: Yes. Therefore you don't need the environment split. You can work with align and \notag: tex.stackexchange.com/questions/26425/… –  Marco Daniel Oct 4 '13 at 9:56

This at least compiles and produces output. Removed the extra closing brace in \usepackage{breqn}} and the extra \ in \end{\equation}, and commented out the \begin{comment}, \end{comment} blocks. Plus I think you had some extra blank lines that I removed, and I think the quad was intended to be \quad. Hope this gets you going...

\documentclass{article}%
\usepackage{amsmath}%
\usepackage{amsfonts}%
\usepackage{amssymb}%
\usepackage{graphicx}
\usepackage{verbatim}
\usepackage{breqn}
%-------------------------------------------

\begin{document}
%this equation 1 is ok
$$g\left[Pr(happy_{im}=1)\right]=\alpha_{0i}+\alpha_{1}.\left|living\_shock_{im}\right|+\epsilon_{im} \label{Original}$$
%this equation 2 is ok
$$g\left[Pr(happy_{im}=1)\right]=\alpha_{0i}+\alpha_{1}.\left|living\_shock_{im}\right|+\beta.{year}+\epsilon_{im} \label{yearlytrend}$$

%to split3
%have commented it out as no pdf output is produced otherwise
%\begin{comment}
$$\begin{split} g\left[Pr(happy_{im}=1)\right]=\alpha_{0i}+\alpha_{1}. \left|living\_shock_{im}\right|+\\ \quad+\beta.{year}+\gamma.region. \left|living\_shock_{im}\right|+\delta{region}+\epsilon_{im} \label{region} \end{split}$$
%\end{comment}

%again no output produced when {dmath} environment of breqn used; commented out
%\begin{comment}
%to split4
\begin{dmath}
g\left[Pr(happy_{im}=1)\right]=\alpha_{0i}+\alpha_{1}.\left|
living\_shock_{im}\right|+\beta.{year}+//+\gamma.demo_{iy}.\left|
living\_shock_{im}\right|+\delta_{iy}.demo_{iy}+\epsilon_{im}
\label{demo}
\end{dmath}
%\end{comment}

%to split5
$$\begin{split} g\left[Pr(happy_{im}=1)\right]=\alpha_{0i}+\alpha_{1}.\left|living\_shock_{im}\right|+\beta.{year}+\gamma_{1}.demo_{iy}.\\ \left|living\_shock_{im}\right|+\gamma_{2}.urbanpop\%_{iy}.\left|living\_shock_{im} \right|+\delta_{1}.demo_{iy}+\delta_{2}.urbanpop\%_{iy}+\delta_{3}.population+\epsilon_{im} \label{size} \end{split}$$

\end{document}
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