Formula Font Size in An Array or Equation?

Question

    \begin{equation} 
    \left\{
    \begin{array}{l} 
    {\bar{\varphi }_{1} =\frac{d_{1} }{d_{1} +d_{n} } \varphi _{n} } \\ 
    {\bar{\varphi }_{i} =\frac{d_{i} }{d_{i} +d_{i-1} } \varphi _{i-1} ,\qquad i=2,...,n-1} \\ 
    {\bar{\varphi }_{n} =\frac{d_{n} }{d_{n} +d_{n-1} } \varphi _{n-1}  } \end{array}
    \right.  
    \end{equation} 

The above Latex code shows the formula as follows:

It looks really ugle because letters in fractions are very small but the right part i=2,...,n-1 is large. Especially, n-1 looks just too long. Is there any way to beautify this or is is it the normal way of showing this formula?

Answer 1

Consider using dcases from mathtools:

\documentclass{article}

\usepackage{mathtools}

\begin{document}

\begin{equation}
  \begin{dcases}
    \bar{\varphi}_1 = \frac{ d_1 }{ d_1 + d_n }     \varphi_n                        \\ 
    \bar{\varphi}_i = \frac{ d_i }{ d_i + d_{i-1} } \varphi_{i-1}, & i = 2,\dots,n-1 \\ 
    \bar{\varphi}_n = \frac{ d_n }{ d_n + d_{n-1} } \varphi_{n-1}
  \end{dcases}
\end{equation}

\end{document}

dcases places all the content within the construction is \displaystyle, resulting in the typical larger-format \frac display (similar to \dfrac from amsmath).

Answer 2

Below code helps you to improve the quality:

 \begin{equation} 
\begin{cases}
    \bar{\varphi }_{1} &=\dfrac{d_{1} }{d_{1} +d_{n} } \varphi _{n} \\[6pt]
    \bar{\varphi }_{i} &=\dfrac{d_{i} }{d_{i} +d_{i-1} } \varphi _{i-1} ,\qquad i=2,...,n-1 \\[6pt] 
    \bar{\varphi }_{n} &=\frac{d_{n} }{d_{n} +d_{n-1} } \varphi _{n-1}  
    \end{cases}
    \end{equation}