How can I use a downward arrow in a formulae as the below example:
There are some examples in other formats same as using $\underbrace{x}_{y}$ in equations but I could not find a desired style of an equation.
Using downward arrow in an equation
equations
Related Solutions
Use \tag for getting the main number:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{subequations}\label{first:main}
First some separate equations
\begin{equation}
1=1 \tag{\ref{first:main}}
\end{equation}
and another
\begin{equation}
1>0 \label{first:a}
\end{equation}
and another
\begin{equation}
1<2 \label{first:b}
\end{equation}
\end{subequations}
\begin{subequations}\label{second:main}
But it works also with \texttt{align} and the other alignment
environments
\begin{align}
1 &= 1 \tag{\ref{second:main}}\\
1 &> 0 \label{second:a}\\
1 &< 2 \label{second:b}
\end{align}
and you can reference all of them, as seen below.
\end{subequations}
Here are some references: \eqref{first:main}, \eqref{first:a}
and \eqref{second:b}.
\end{document}
There are a couple of flaws in your document.
- You use
\xdef{\unexpanded...}. This is essentially\gdef, which totally suffices here. - Your use of
\unexpandedis wrong.\unexpandedexpects a balanced token list delimited by explicit{,}. If you want to protect a single token from expansion in\edef, use\noexpand. Enrico wrote a nice answer about that. - You use
eqnarray. Never useeqnarray. \tagdoes not work ineqnarray.
Here is a fixed version.
\documentclass{article}
\usepackage{amsmath}
\newcommand{\restatableeq}[3]{\label{#3}#2\gdef#1{#2\tag{\ref{#3}}}}
\begin{document}
\begin{align}
\restatableeq{\eqone}{This & is & eqation 1}{eq1}\\
Another & simple & equation
\end{align}
\begin{align}
One & more & equation\\
\restatableeq{\eqtwo}{This & is & eqation 2}{eq2}
\end{align}
Here, we use (\ref{eq1}) and (\ref{eq2}) again:
\begin{align*}
\eqone\\
\eqtwo
\end{align*}
\end{document}
Best Answer
This could be done in a variety of ways as in the answers to this question, or you could use an
alignenvironment, using theBcharacter. The\downarrowneeds a small shift to the left as shown:If you want to adjust the spacing around the arrow, you can add negative space after the appropriate lines: