How to make the cases bracket in an equation more elegant?

Question

I am writing an equation containing cases using the following codes:

\begin{equation}
\Delta A = 
\begin{cases}
    \frac{\pi \left( 1-\mu \right) d_i^2}{42GW_c} & \text{if } a = 0\\
        0                                  & \text{if } a = 1
    \end{cases}                                                                                                 
\end{equation}

It worked fine but the output is not beautiful, I want to make the left brace smaller, could someone tell me how to deal with it?

Answer 1

Maybe the brace obtained with empheq will be more like you want?

\documentclass{article}
\usepackage{empheq}

\begin{document}

\begin{empheq}[left={\Delta A =\empheqlbrace}]{equation}
  \begin{aligned}
      &\frac{\pi \left( 1-\mu \right) d_i^2}{42GW_c} & & \text{if } a = 0\\[1ex]
      & 0 & & \text{if } a = 1
  \end{aligned}
\end{empheq}

\end{document} 

Answer 2

The output by the conventional cases looks good, but it is possible to do this with tikz and nicematrix to provide flexibility in adjusting the braces thickness to your taste.

\documentclass{amsart}
\usepackage{nicematrix}
\usepackage{tikz}

\usetikzlibrary{decorations.pathreplacing,calligraphy}

\tikzset{
    BraceMirrored/.style = {decorate,
        decoration={calligraphic brace, amplitude=2pt,
            pre =moveto, pre  length=1.1pt,
            post=moveto, post length=1.1pt,
            mirror,
            raise=#1},
        thick,
        pen colour=black},
        BraceMirrored/.default=0pt
}

\begin{document}

\begin{equation*}
    \everymath{\displaystyle}
        \Delta A = \mspace{11mu}
        \begin{NiceArray}{@{}l @{\quad}l}[cell-space-limits=1.1pt]
            \frac{\pi \left( 1-\mu \right) d_i^2}{42GW_c} & \text{if $a = 0$}
        \\
            0 & \text{if $a = 1$} 
            \CodeAfter
            {
                \begin{tikzpicture}
                    \draw[BraceMirrored={3.7pt}, thin] (1-1.north west) -- node[left=3.7pt] {} (2-1.south west); % change thickness by including `thin`, 'very thin', or 'ultra thin'
                \end{tikzpicture}
            }
        \end{NiceArray}
\end{equation*}

\end{document}

Answer 3

Is this what You need?

\documentclass{extreport}
\usepackage{amsmath}


\begin{document}

\begin{equation}
\Delta A = 
\begin{cases}
    \dfrac{\pi \left( 1-\mu \right) d_i^2}{42GW_c} & \text{if } a = 0\\
        0                                  & \text{if } a = 1
    \end{cases}                                        
\end{equation}


\end{document}

Answer 4

In the Elsevier's double column template, the cas-dc documentclass loads the stix package, which causes your problem. If you write \PassOptionsToPackage{nomath}{stix} into the first line of the source, this effect will be disappeared.