Add Superscripts and Subscripts for Arrows in LaTeX Equation Environment

Oct. 05, 2023

In LaTeX, amsmath [1] and extarrows (extensible arrows) [2] macro package provide a set of control sequences to realize adding text over or under the arrows [3, p254]:

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\documentclass{article}
\usepackage{amsmath}
\usepackage{extarrows}

\begin{document}
	\begin{equation*}
		\begin{aligned}
			&A\xleftarrow[a+b+c+d+e]{xyz}Z\qquad & A\xrightarrow[a+b+c+d+e]{xyz}Z\\
			&A\xlongleftarrow[a+b+c+d+e]{xyz}Z\qquad & A\xlongrightarrow[a+b+c+d+e]{xyz}Z\\
			&A\xLongleftarrow[a+b+c+d+e]{xyz}Z\qquad & A\xLongrightarrow[a+b+c+d+e]{xyz}Z\\
			&A\xleftrightarrow[a+b+c+d+e]{xyz}Z\qquad & A\xLeftrightarrow[a+b+c+d+e]{xyz}Z\\
			&A\xlongleftrightarrow[a+b+c+d+e]{xyz}Z\qquad & A\xLongleftrightarrow[a+b+c+d+e]{xyz}Z\\
			&A\xlongequal[a+b+c+d+e]{xyz}Z
		\end{aligned}
	\end{equation*}
\end{document}

image-20231005160240672

\xleftarrow and \xrightarrow produce arrows that extend automatically to accommodate unusually wide subscripts or superscripts. [1, p15]

Note that:

(1) The control sequences \xleftarrow and \xrightarrow are from amsmath package, whereas the others are from extarrows package. Therefore, some control sequences are not available in the equation environment of .md files:

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\begin{aligned}
    &A\xleftarrow[a+b+c+d+e]{xyz}Z & A\xrightarrow[a+b+c+d+e]{xyz}Z\\
    &A\xlongleftarrow[a+b+c+d+e]{xyz}Z & A\xlongrightarrow[a+b+c+d+e]{xyz}Z\\
    &A\xLongleftarrow[a+b+c+d+e]{xyz}Z & A\xLongrightarrow[a+b+c+d+e]{xyz}Z\\
    &A\xleftrightarrow[a+b+c+d+e]{xyz}Z & A\xLeftrightarrow[a+b+c+d+e]{xyz}Z\\
    &A\xlongleftrightarrow[a+b+c+d+e]{xyz}Z & A\xLongleftrightarrow[a+b+c+d+e]{xyz}Z\\
    &A\xlongequal[a+b+c+d+e]{xyz}Z
\end{aligned}

image-20231005160738413

(2) The control sequences which are included with long or Long word will create long arrows compared with that without it, when the text content over or under arrow is short. For example:

image-20231005160405496

image-20231005162534355


On the other hand, the goal could be realized by \ce control sequence [3, p227]:

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\begin{split}
    &\ce{2H2 + O2 ->[\text{combustion}] 2H2O}\\
    &\ce{2H2O + O2 <-[\text{decomposition}] 2H2O2}\\
\end{split}
\[\begin{split} &\ce{2H2 + O2 ->[\text{combustion}] 2H2O}\\ &\ce{2H2O + O2 <-[\text{decomposition}] 2H2O2}\\ \end{split}\]

However, \ce is from mhchem macro package [5], which is for typesetting professional chemical formulas or equations, so the grammar of \ce is kind of different compared that used in traditional equation environment. \ce could be directly used in the equation environment of .md files.


P.S. At the beginning, I mistakenly think that the control sequences like \overleftarrow and \underleftarrow [3, p228], which are also from amsmath package, could realize the goal.

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\begin{split}
    &\overleftarrow{text}\\
    &\overrightarrow{text}\\
    &\overleftrightarrow{text}\\
    &\underleftarrow{text}\\
    &\underrightarrow{text}\\
    &\underleftrightarrow{text}\\
\end{split}
\[\begin{split} &\overleftarrow{text}\\ &\overrightarrow{text}\\ &\overleftrightarrow{text}\\ &\underleftarrow{text}\\ &\underrightarrow{text}\\ &\underleftrightarrow{text}\\ \end{split}\]

But actually, they are just for adding arrows over or under the text content, whose role are like \overline and underline.

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a\overleftarrow{text}b,\quad a\underleftarrow{text}b
\[a\overleftarrow{text}b,\quad a\underleftarrow{text}b\]


References

[1] amsldoc.pdf.

[2] CTAN: /tex-archive/macros/latex/contrib/extarrows.

[3] 刘海洋编著. LaTeX入门. 北京: 电子工业出版社, 2013.6.

[4] Composing and Decomposing Matter.

[5] CTAN: Package mhchem.