[Tex/LaTex] How to control the font size in complex fractions?

fractions

I am writing an equation and for part of that, I have the following fraction:

\begin{eqnarray}
\frac{u_{fe}\frac{\frac{u_{i,j,k}^n+u_{i,j,k}^{*}}{2}+    
\frac{u_{i+1,j,k}^n+u_{i+1,j,k}^{*}}{2}}{2}-
u_{fw}\frac{\frac{u_{i,j,k}^n+u_{i,j,k}^{*}}{2}+
\frac{u_{i-1,j,k}^n+u_{i-1,j,k}^{*}}{2}}{2}}
{dx_i + dx_{i+1}}
\end{eqnarray}

enter image description here

My problem is that the size of u in u_{fe} and u_{i,j,k} is different. I have also tried equation, gather and split but the problem is still there.
`
Any suggestion is appreciated.

Best Answer

Here is a suggestion: stop the madness. All those fractions bars are confusing and make the expression diffcult to read. Don't inflict that on your readers. If you had complicated denominators, I would understand, but here it's preferable, in my opinion, to keep "one level of fraction", by putting most 1/2 factors in front of the expressions they multiply. See below.

enter image description here

\documentclass{article}

\usepackage{amsmath}

\begin{document}
\begin{multline}
    \frac{1}{dx_i + dx_{i+1}}
    \left(  
        \frac{u_{fe}}{2}
        \left(
            \frac{u_{i,j,k}^n+u_{i,j,k}^{*}}{2} +
            \frac{u_{i+1,j,k}^n+u_{i+1,j,k}^{*}}{2}
        \right)
        +
    \right. \\
    \left.
        \frac{u_{fw}}{2}
        \left(
            \frac{u_{i,j,k}^n+u_{i,j,k}^{*}}{2} +
            \frac{u_{i-1,j,k}^n+u_{i-1,j,k}^{*}}{2}
        \right)
    \right)
\end{multline}
\end{document}
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