# Using split to break a long equation

I am trying to break a long equation over multiple lines. It is here as follows:

$$\begin{split} L(\textbf{q})=&\prod_{t=0}^{36}{q_{1}^{iB(t)sB(t+1)+iC(t)sC(t+1)}\\ &\quad\cdot q_{2}^{i(t)sA(t+1)+(iA(t)+iC(t))sB(t+1)+(iA(t)+iB(t))sC(t+1)}\\ &\quad\cdot(1-q_{2}^{i(t)})^{sA(t)-sA(t+1)}\\ &\quad\cdot(1-q_{1}^{iB(t)}q_{2}^{iA(t)+iC(t)})^{sB(t)-sB(t+1)}\\ &\quad\cdot(1-q_{1}^{iC(t)}q_{2}^{iA(t)+iB(t)})^{sC(t)-sC(t+1)}} \end{split}$$


But when I try and pdflatex the file, I get !Missing } inserted. And it doesn't run. I don't know why it's trying to put in extra brackets when they are not needed. And the file runs without the split environment (but I need to put it in since otherwise the equation flows off the page)

Any help??

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Remove first { in {q_{1}^{, first line and the last } in -sC(t+1)}} last line. – Harish Kumar Mar 29 '13 at 13:15
Welcome to TeX.SX. A tip: If you indent lines by 4 spaces, then they're marked as a code sample. You can also highlight the code and click the "code" button ({}) or hit Ctrl+K. – Claudio Fiandrino Mar 29 '13 at 13:29
You can make this much easier by replacing all the exponents with some simple notations and explain them separately. – g.kov Mar 29 '13 at 14:27
It's a common misconception to think that one has to write \prod_{i=1}^{n}{a_{i}}; while the braces for the limits are necessary, those around a_{i} aren't and actually shouldn't be used. – egreg Mar 29 '13 at 14:41
Also, just so you know, it's best to use \mathbf{q} to get a bold upright q in math. For instance, if this equation was inside a theorem whose text was set in italic, the \textbf{q} would render as a bold italic q; but a \mathbf{q} would still render as a bold upright q. – MSC Mar 29 '13 at 16:12

Here is a working version of your code. You don't need to wrap the product itself into {}. For real grouping I used curly braces.

Implementation

\documentclass{standalone}
\usepackage{amsmath}
\usepackage{bm}
\begin{document}
$$\begin{split} L(\bm{q}) &= \prod\limits_{t=0}^{36} \Bigl\{ q_{1}^{iB(t)sB(t+1)+iC(t)sC(t+1)} \\ &\quad \cdot q_{2}^{i(t)sA(t+1)+(iA(t)+iC(t))sB(t+1)+(iA(t)+iB(t))sC(t+1)} \\ &\quad \cdot (1-q_{2}^{i(t)})^{sA(t)-sA(t+1)} \\ &\quad \cdot (1-q_{1}^{iB(t)}q_{2}^{iA(t)+iC(t)})^{sB(t)-sB(t+1)} \\ &\quad \cdot (1-q_{1}^{iC(t)}q_{2}^{iA(t)+iB(t)})^{sC(t)-sC(t+1)} \Bigr\} \end{split}$$
\end{document}


Output

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I would align the subsequent factors under the first factor, not the \prod. – mafp May 22 '13 at 10:26
I like your suggestion, but according to the question, this is what OP wanted. – Henri Menke May 22 '13 at 16:24