如何解决括号[]太小的问题

Question

\begin{equation}\label{eq:14}
\begin{split}
\Pi&=\Pi_{2n}+\Pi_{2l}+\Pi_{2h}\\&= \bigg[
    \begin{split}
      &q_{2 n} \left(-\alpha  A_0 \beta  k \left(1-s_{2 h}\right)-(1-\alpha ) A_0 k \left(1-s_{2 l}\right)-c_n-c_{\text{nature}}-k q_{2 n}+\delta _m\right)\\&+\alpha  A_0 \beta  \left(1-s_{2 h}\right) \left(-(1-\alpha ) A_0 k \lambda _h \left(1-s_{2 l}\right)-\alpha  A_0 \beta  k \lambda _h \left(1-s_{2 h}\right)-c_h-k \lambda _h q_{2 n}+\lambda _h \delta _m-s_{2 h}\right)\\&+(1-\alpha ) A_0 \left(1-s_{2 l}\right) \left(-\alpha A_0 \beta  k \left(1-s_{2 h}\right) \lambda _l-(1-\alpha ) A_0 k \lambda _l \left(1-s_{2 l}\right)-c_l-k \lambda _l q_{2 n}+\lambda _l \delta _m-s_{2 l}\right)
    \end{split}
   \bigg]
\end{split}
\end{equation}

如下所示，“[]”太小了……

Answer 1

您可以像使用一样生成任意大小的分隔符\left，但在这里我可能会采用另一种方式，根本不使用括号

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\begin{multline}\label{eq:zz}%dont use numbers
\Pi=\Pi_{2n}+\Pi_{2l}+\Pi_{2h}\\
= \begin{aligned}[t]
     &q_{2 n} (-\alpha  A_0 \beta  k (1-s_{2 h})-(1-\alpha ) A_0 k (1-s_{2 l})\\
&\qquad{}-c_n-c_{\mathrm{nature}}-k q_{2 n}+\delta _m)\\
&\qquad{}+\alpha  A_0 \beta (1-s_{2 h}) (-(1-\alpha ) A_0 k \lambda _h (1-s_{2 l})\\
&\qquad{} -\alpha  A_0 \beta  k \lambda _h (1-s_{2 h})-c_h-k \lambda _h q_{2 n}+\lambda _h \delta _m-s_{2 h})\\
&\qquad{}+(1-\alpha ) A_0 (1-s_{2 l}) (-\alpha A_0 \beta  k (1-s_{2 h}) \lambda _l\\
&\qquad{}-(1-\alpha ) A_0 k \lambda _l (1-s_{2 l})-c_l-k \lambda _l q_{2 n}+\lambda _l \delta _m-s_{2 l})
\end{aligned}
\end{multline}

\end{document}

请注意，如果您确实使用固定大小，则始终使用\biggl(和而\biggr)不是\bigg(和\bigg)以确保正确的 mathopen 和 mathclose 间距。

Answer 2

我提出了一种变体布局，结合了flalign和：alignedalignedat

\documentclass{article}

\usepackage{mathtools}

\begin{document}

\begin{flalign}\label{eq:zz}%dont use numbers
 & \begin{alignedat}{2}
\Pi & =\mathrlap{\Pi_{2n}+\Pi_{2l}+\Pi_{2h}}\\
 & = q_{2 n} \bigl(\mkern-4mu&& -\alpha A_0 \beta k (1-s_{2 h})-\mathrlap{(1-\alpha ) A_0 k (1-s_{2 l})-c_n-c_{\mathrm{nature}}-k q_{2 n}+\delta _m\bigr)}\\
 & & \mathrlap{\begin{aligned}[t] {} +\alpha A_0 \beta (1-s_{2 h}) \bigl(-(1-\alpha ) A_0 k \lambda _h (1 -s_{2 l}) -\alpha A_0 \beta k \lambda _h (1-s_{2 h})\\
{}-c_h-k \lambda _h q_{2 n}+\lambda _h \delta _m-s_{2 h}\bigr)
\end{aligned}}\\
& & \mathrlap{\begin{aligned}[t] {} +(1-\alpha ) A_0 (1-s_{2 l})\bigl (-\alpha A_0 \beta k (1-s_{2 h}) \lambda _l-(1-\alpha ) A_0 k \lambda _l (1-s_{2 l})\\
 {}-c_l-k \lambda _l q_{2 n}+\lambda _l \delta _m -s_{2 l}\bigr)%
 \end{aligned}}\\
\end{alignedat} & &
\end{flalign}

\end{document}