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I have seen a number of questions detailing specific means for how to break down a given equation, however I am more interested in the design at this point. That is, I'm not sure what part of this equation is suitable to be split. I have an equation that will not fit in a single column as is:

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}
\begin{equation}
  p_{ij,k} = \begin{cases}
    \frac{
      [\tau_{ij,1}]^{\lambda_k \alpha} \cdot [\tau_{ij,2}]^{(1-\lambda_k)\alpha} \cdot   [\eta_{ij,1}]^{\lambda_k \beta} \cdot [\eta_{ij,2}]^{(1-\lambda_k)\beta}
    }
    {
      \sum_{h \in N_i} [\tau_{ih,1}]^{\lambda_k \alpha} \cdot [\tau_{ih,2}]^{(1-\lambda_k)\alpha} \cdot [\eta_{ih,1}]^{\lambda_k \beta} \cdot [\eta_{ih,2}]^{(1-\lambda_k)\beta}
    } & \textrm{ if }j \in N_i \\
    0&\textrm{ otherwise} \\
  \end{cases}
\end{equation}
\end{document}​

The problem is that both the numerator and the denominator would need to be split, and I'm not sure of a way to do this that would still look appropriate. Any suggestions?

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3 Answers 3

up vote 5 down vote accepted

I might consider taking a slightly different approach, and use something like the following

enter image description here

This allows you to split f and g as you like

\documentclass{article}

\usepackage{mathtools}


\begin{document}

We have that
\[
p_{ij,k} = \begin{dcases}
\frac{f(\tau,\eta)}{g(\tau,\eta)}& \textrm{ if }j \in N_i\\
0&\textrm{ otherwise}\\
\end{dcases}
\]
where
\begin{align*}
f(\tau,\eta)&=[\tau_{ij,1}]^{\lambda_k \alpha} \cdot [\tau_{ij,2}]^{(1-\lambda_k)\alpha} 
            \cdot   [\eta_{ij,1}]^{\lambda_k \beta} \cdot [\eta_{ij,2}]^{(1-\lambda_k)\beta}\\
g(\tau,\eta)&=\sum_{h \in N_i} [\tau_{ih,1}]^{\lambda_k \alpha} \cdot [\tau_{ih,2}]^{(1-\lambda_k)\alpha} 
            \cdot [\eta_{ih,1}]^{\lambda_k \beta} \cdot [\eta_{ih,2}]^{(1-\lambda_k)\beta}
\end{align*}

\end{document}

Note that dcases is from the mathtools package. If the journal you're submitting doesn't have this, you could replace it with cases but the display won't be quite as good.

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I thought it might come to that. Very elegant. Thanks. –  Andrew Jan 31 '12 at 20:15

best I could come up with was:

\documentclass{amsart}

\begin{document}

\begin{equation}
p_{ij,k} = \begin{cases}
\dfrac{
\begin{split}
  [\tau_{ij,1}]^{\lambda_k \alpha} \cdot [\tau_{ij,2}]^{(1-\lambda_k)\alpha} \cdot \qquad\\  
[\eta_{ij,1}]^{\lambda_k \beta} \cdot [\eta_{ij,2}]^{(1-\lambda_k)\beta}
\end{split}
}{
\begin{split}
\sum_{h \in N_i} [\tau_{ih,1}]^{\lambda_k \alpha} \cdot [\tau_{ih,2}]^{(1-\lambda_k)\alpha} \cdot \qquad\\
[\eta_{ih,1}]^{\lambda_k \beta} \cdot [\eta_{ih,2}]^{(1-\lambda_k)\beta}
\end{split}
}& \textrm{ if }j \in N_i\\
0&\textrm{ otherwise}\\
\end{cases}
\end{equation}

\end{document}
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Greatly appreciate the effort, but I don't think a journal will accept it. –  Andrew Jan 31 '12 at 20:09
2  
Ah If it's a journal their copy editors will reformat it anyway so just send it as it is:-) Otherwise as suggested in the other answer introducing some local definitions to restructure the expression is probably the way to go. –  David Carlisle Jan 31 '12 at 20:13

use \sum\limits_{h \in N_i} for the sum. It needs less space. And use \text instead of \textrm

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2  
This seems more like a comment than an answer. Would you agree? –  Werner Jan 31 '12 at 20:15
    
no, I don't agree –  Herbert Jan 31 '12 at 20:24

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