I am preparing a collection of the most useful formulas for an exam and I would like to have a brief explanation for each one of them.

Since this is supposed to be a quick reference I'd prefer to pack all the formulas together with no text or whatsoever and then link them to their explanation that I could put in another page. What could I do to achieve this?

Manually cross-linking with \autoref kind of beats the purpose, it would take me too long and would be hard to maintain since there's an awful lot of equations to write.

## Edit: What I currently have

As suggested in the comments, I'll add a section that I currently have.

\section{Pulsed Radar}
\subsection{Characteristics}
\begin{align}
f_r &= \frac{1}{T}
&\text{Pulse Repetition Frequency (PRF)} \label{basic:PRF_vs_PRI} \\
&&\text{and Pulse Repetition Interval (PRI)} \nonumber
\\
\tau &= \frac{1}{B}
&\text{Bandwidth}
\label{basic:BW}
\\
d_t &= \frac{\tau}{T}
&\text{Duty cycle}
\end{align}

\subsection{Range}
\begin{align}
R &= \frac{c}{2t}
&\text{Range}
\\
R_\text{max} &= \frac{c}{2T}
&\text{Max. unambiguous range} \\
&&\text{(see \autoref{basic:PRF_vs_PRI})} \nonumber
\\
R_\text{min} &= \delta R = \frac{c}{2\tau}
&\text{Minimum range or range resolution} \\
&&\text{(see \autoref{basic:BW})} \nonumber
\\
M &= \frac{R_\text{max} - R_\text{min}}{\delta R}
&\text{Number of space bins (} R_\text{min} = \delta R \text{)}
\end{align}


Which gives me this:

As you can see, I currently have the comments right next to the equations, but I want to move them to their own section, so that I can make them just a bit more expressive.

What I have in mind is something like a \footnote, where I write the note and it gets automatically numbered, linked and moved at the bottom of the page - I don't want to manually label every single comment and put a link to it next to the relative equation. The only actual difference from a footnote is that I don't want the text at the bottom of the page - but at the end of the document - and I want it formatted normally.

## Edit 2: why I want it

I want to explain why I have the idea of separating equations from comments: this would allow me to write the formulas in more columns, so that everything is more compact!

• Welcome ! LaTeX reference system works for very large documents such as thesis or book, so I feel pretty confident that the amount of formulas you count on using will be much in the standards. What easier way would you fancy ? May 31 '20 at 12:51
• It would help if you gave a specific example of, say, 3 or 4 formulas and their associated brief explanations that you intend to see linked (hyperlinked?) automatically to each other. Please also provide an idea of what you would consider to be an acceptable or useful way to list the equations.
– Mico
May 31 '20 at 13:07
• I edited the post so I included what I have to give a better idea of what I mean. So, also answering to @BambOo, I'm not worried about latex not being able to handle the number of equations. But since the document only has equations and comments - and each equation has its comment - I was wandering if there was a better way of handling this instead of manually adding a label and then an autoref every other line. May 31 '20 at 14:00
• An "endnotes" approach might satisfy your requirements. Text is entered near its referent, and output separately at the end. There are several good packages; search for "endnotes" and "enotez" on CTAN. Unfortunately, I don't know how any of these fare when embedded in a display math structure. May 31 '20 at 18:59

(updated the answer to switch to multicolumn mode automatically if no explanations are to be shown)

My proposed solution is admittedly not a direct answer to your query. Instead, I suggest taking an indirect approach -- specifically, creating two separate but parallel documents: One with just the formulas, the other with the formulas and their (brief or wordy) explanations. Because all explanations reside inside \tbox ("textual parbox") macros, switching back and forth between the two manifestations is as easy as changing \ifshowtbox from false to true (or vice versa) and recompiling the document.

First, here's how the document would look if \ifshowtbox is set to true, i.e., if the explanations contained in the \tbox directives are supposed to be shown:

And here's how the document would look if \ifshowtbox is set to false. Observe that the columns are much narrower now since we've also switched to 3-column mode.

\documentclass{article}
\usepackage[letterpaper,margin=1in]{geometry} % set page parameters suitably
\usepackage{multicol} % for 'multicols' env.
\usepackage[mathindent]{amsmath} % for 'align' env.
\allowdisplaybreaks

%% create a new conditional: '\showtbox'
\newif\ifshowtbox\showtboxfalse % or "\showtboxtrue"
\ifshowtbox
\newcommand\tbox[1]{\parbox[t]{0.5\textwidth}{\raggedright #1}}
\else
\newcommand\tbox[1]{}
\setlength\mathindent{10pt} % default: 25pt
\fi

\begin{document}
\stepcounter{section} % just for this example

\ifshowtbox\else\begin{multicols*}{3}\fi

\subsection{Characteristics}
\begin{align}
f_r &= \frac{1}{T}
&&\tbox{Pulse Repetition Frequency (PRF) and Pulse Repetition Interval (PRI)}
\label{basic:PRF_vs_PRI}
\\
\tau &= \frac{1}{B}
&&\tbox{Bandwidth}
\label{basic:BW}
\\[1ex]
d_t &= \frac{\tau}{T}
&&\tbox{Duty cycle}
\end{align}

\subsection{Range}
\begin{align}
R &= \frac{c}{2t}
&&\tbox{Range}
\\[1ex]
R_{\max} &= \frac{c}{2T}
&&\tbox{Max.\ unambiguous range; cf. \cref{basic:PRF_vs_PRI}}
\\
R_{\min} &= \delta R = \frac{c}{2\tau}
&&\tbox{Min.\ range or range resolution; cf.  \cref{basic:BW}}
\\
M &= \frac{R_{\max} - R_{\min}}{\delta R}
&&\tbox{Number of space bins ($R_{\min} = \delta R$)}
\end{align}

\ifshowtbox\else\end{multicols*}\fi

\end{document}

• Well yes this is definitely a better solution than what I had! Especially for the simplicity of switching and the fact that I don’t have to break lines manually. I still hope to find a way to separate stuff, especially because I’d like to write equations in more columns if I can, so that everything is more compact! May 31 '20 at 18:28
• @Shishka - Glad you didn''t reject the basic idea of the proposed solution. About switching to multicolumn mode when no explanations are displayed: I'll update my answer to show that it's a piece of cake to switch to, say, 3-column mode automatically if \showtbox is false.
– Mico
May 31 '20 at 18:50

After Barbara's comment:

An "endnotes" approach might satisfy your requirements. Text is entered near its referent, and output separately at the end. There are several good packages; search for "endnotes" and "enotez" on CTAN. Unfortunately, I don't know how any of these fare when embedded in a display math structure. – barbara beeton

I checked the package enotez, which is fairly simple to use and does what I needed. So I edited my document like this:

\section{Pulsed Radar}
\subsection{Characteristics}
\begin{multicols}{2} \noindent
$$f_r = \frac{1}{T} \ \endnote{Pulse Repetition Interval (PRF) versus Pulse Repetition Interval (PRI)}$$
$$\tau = \frac{1}{B} \ \endnote{Bandwidth}$$
\end{multicols}

\subsection{Range}
\begin{multicols}{4} \noindent
$$R = \frac{c}{2t} \ \endnote{Range}$$
$$R_\text{max} = \frac{c}{2T} \ \endnote{Max. unambiguous range}$$
$$R_\text{min} = \delta R = \frac{c}{2 \tau} \ \endnote{Min. range or range resolution}$$
$$\theta_B = R \frac{\lambda}{d} \ \endnote{Azimuth resolution; d is the length of the antenna}$$
$$M = \frac{R_\text{max} - R_\text{min}}{\delta R} \ \endnote{Number of space bins}$$
\end{multicols}

\subsection{Power}
\begin{multicols}{2} \noindent
$$d_t = \frac{\tau}{T} \ \endnote{Duty Cycle}$$
$$P_\text{avg} = P_t \cdot d_t \ \endnote{Average power}$$
\end{multicols}
\printendnotes[itemize]


Which gives me this:

It's probably not the best solution because I had to give up the \align environment since, for some reason, all the notes were printed twice. I also gave up references (at least, for now) because defining an equation environment for each equation is too much.

But still, this is fair enough for a quick reference of formulas and comments. Thank you all for your suggestions!