[Tex/LaTex] Suggestions for splitting a large fractional equation

aligncolumnsequationsfractions

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?

Best Answer

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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