fleqn 长公式的奇怪行为

Question

我有一个文档，其中包含几个不同长度的公式，我需要将它们左对齐。为了实现这一点，我使用了fleqn中的选项\documentclass。它对大多数公式都按预期工作，但最长的公式没有缩进，就好像它们不是分开写在一行上的一样：

我怎样才能修复这个问题而不破坏更多行的公式？

---

平均能量损失

\documentclass[fleqn]{article}

\usepackage{indentfirst}
\usepackage{amsmath}

\begin{document}
\subsection*{Lorem ipsum sit amet}
Short formula: aligned as wanted (the quick brown fox jumps over the lazy dog and the quick brown fox jumps over the lazy dog)
\[\begin{split}
    V_{x}           & = \frac{V_{0} - \sum_{m}^{n}Sp + \sum_{m}^{n}Pr} {q^{(n-m)}} = \\
                    & = 10000
\end{split}\]

Longer formula: aligned as wanted (the quick brown fox jumps over the lazy dog and the quick brown fox jumps over the lazy dog)
\[\begin{split}
    \sum_{x}^{y}Sp & = \bigg(1000\frac{q^a-1}{r}q^{b}
                        + 2000\frac{q^{c}-1}{r}q^d\bigg)
                        + \bigg(3000\frac{q^e-1}{r}q
                        + 4000\bigg) = \\
                    & = 5000
\end{split}\]

Even longer formula: oddly aligned (the quick brown fox jumps over the lazy dog and the quick brown fox jumps over the lazy dog)
\[\begin{split}
    \sum_{x}^{y}Pr & = \bigg(100000\frac{q^a-1}{r}q^{b}
                        + 200000\frac{q^{c}-1}{r}q^d\bigg)
                        + \bigg(300000\frac{q^e-1}{r}q
                        + 400000\bigg) = \\
                    & = 500000
\end{split}\]

\end{document}

Answer 1

没有奇怪的行为。公式不符合该线，LaTeX 会尽力适应它。

分割过长的线。

注意。使用\biggland \biggr，而不是未加修饰的\bigg。另外，通常不会重复等号（但您的印刷传统可能会要求这样做；请尽量避免这样做，因为没有必要）。

\documentclass[fleqn]{article}

\usepackage{indentfirst}
\usepackage{amsmath}

\begin{document}
\subsection*{Lorem ipsum sit amet}
Short formula: aligned as wanted (the quick brown fox jumps over the 
lazy dog and the quick brown fox jumps over the lazy dog)
\[\begin{split}
    V_{x}           & = \frac{V_{0} - \sum_{m}^{n}Sp + \sum_{m}^{n}Pr} {q^{(n-m)}} \\
                    & = 10000
\end{split}\]

Longer formula: aligned as wanted (the quick brown fox jumps over the 
lazy dog and the quick brown fox jumps over the lazy dog)
\[\begin{split}
    \sum_{x}^{y}Sp & = \biggl(1000\frac{q^a-1}{r}q^{b}
                        + 2000\frac{q^{c}-1}{r}q^d\biggr)
                        + \biggl(3000\frac{q^e-1}{r}q
                        + 4000\biggr)\\
                    & = 5000
\end{split}\]

Even longer formula: oddly aligned (the quick brown fox jumps over the 
lazy dog and the quick brown fox jumps over the lazy dog)
\[\begin{split}
    \sum_{x}^{y}Pr & = \biggl(100000\frac{q^a-1}{r}q^{b}
                        + 200000\frac{q^{c}-1}{r}q^d\biggr) \\
                  &\qquad+ \biggl(300000\frac{q^e-1}{r}q
                        + 400000\biggr) \\
                    & = 500000
\end{split}\]

\end{document}