如何使用 eqnarray 创建一个包含多个方程的框？

Question

我曾尝试只为一个方程式制作一个框，但我不知道如何在不改变方程式位置的情况下为多个方程式制作一个框。这是我的代码，

\begin{eqnarray}
C_n(t) = \delta_{n,i}&-&\frac{i}{\hbar}\int_{-\infty}^{t} d\tau \bra{\psi_n}H_1(\tau)\ket{\psi_i}\exp(i\omega_{ni}t) \nonumber\\
&+& {\Big(-\frac{i}{\hbar}\Big)}^2\int_{-\infty}^{t} d\tau \int_{-\infty}^{\tau} d\tau' \sum_{m} \Big[V_{nm}(\tau')V_{mi}(\tau)\Big]\nonumber\\
&+& {\Big(-\frac{i}{\hbar}\Big)}^3\int_{-\infty}^{t} d\tau \int_{-\infty}^{\tau} d\tau'\int_{-\infty}^{\tau'} d\tau'' \sum_{m,k} \Big[V_{nm}(\tau'')V_{mi}(\tau')V_{ki}(\tau)\Big]\nonumber\\
&+& \dots \nonumber
\end{eqnarray}

Answer 1

您可以使用\boxed和aligned设施amsmath来获得您描述的结果：

\documentclass{article}
\usepackage{amsmath}
\usepackage{braket}
\begin{document}
\thispagestyle{empty}
\[
\boxed{
  \begin{aligned}
  C_n(t) = \delta_{n,i}&-\frac{i}{\hbar}\int_{-\infty}^{t} d\tau \bra{\psi_n}H_1(\tau)\ket{\psi_i}\exp(i\omega_{ni}t) \nonumber\\
    &+ {\Big(-\frac{i}{\hbar}\Big)}^2\int_{-\infty}^{t} d\tau \int_{-\infty}^{\tau} d\tau' \sum_{m} \Big[V_{nm}(\tau')V_{mi}(\tau)\Big]\nonumber\\
    &+ {\Big(-\frac{i}{\hbar}\Big)}^3\int_{-\infty}^{t} d\tau \int_{-\infty}^{\tau} d\tau'\int_{-\infty}^{\tau'} d\tau'' \sum_{m,k} \Big[V_{nm}(\tau'')V_{mi}(\tau')V_{ki}(\tau)\Big]\\
    &+ \dots 
  \end{aligned}
}
\]
\end{document}