# Numbering two sets of equations

There are many question and answers already on the subject, but I have not found any suitable one for my request, so I hope you can help me.

I have two quite big systems of equations, one is the log-linearization of the other. I would like numbering of the form:

\section{First section}
... (1a)
... (2a)
... (3a)
\section{Second section}
... (1b)
... (2b)
... (3b)


where the ellipses stand for equations. As one equation exactly relates to the other, I find this a much better structure in my thesis than simply writing equations (1) to (6). Also, I am not too fixated on the exact notation, so if someone has a better way of doing this, I am eager to here it.

Here is a MWE:

\documentclass[a4paper,12pt]{report}
\usepackage{amsmath,amsfonts,amssymb}
\usepackage{textcomp,mathrsfs,xcolor,float,fancyhdr}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc} \pagenumbering{arabic}

\begin{document}
\chapter{Equilibrium}

\section{Deflated Equilibrium}
$$a=b$$
\begin{align}
b=c \\
c=d
\end{align}
\section{Log-Lin Equilibrium}
$$a=b$$
\begin{align}
b=c \\
c=d
\end{align}

\end{document}}

• \renewcommand{\theequation}{\arabic{equation}\alph{section}} for example? But does allow for 26 sections only, I don't know if this will be enough then ;-) – user31729 Feb 5 '17 at 9:53
• Sadly, it is not. :-) Also, subequations connects equations (1) to (3) and (4) to (6). I am looking for a way to connect (1) and (4), (2) and (5), and (3) and (6) – Chris tie Feb 5 '17 at 9:58
• We need more information on this, a compilable document. I am thinking about an idea with coupled counters but this is only a raw idea – user31729 Feb 5 '17 at 10:01
• I added a MWE, hope that helps! – Chris tie Feb 5 '17 at 10:10
• Are you using equation only? No align environment with more than one line such that those are numbered as well? And how do you settle the connection between, say 1a and 1b-- is this just the order of equations? – user31729 Feb 5 '17 at 10:14

Providing the instructions

\numberwithin{equation}{section}
\renewcommand\theequation{\arabic{equation}\alph{section}}


should let you achieve your formatting objective. That said, you may want to think about what your readers are supposed to learn when they encounter equations numbered, say, "(1a)" in chapters 1, 2, and 3...

\documentclass[a4paper,12pt]{report}
\usepackage{amsmath} % for \numberwithin macro and 'align' env.
\numberwithin{equation}{section} % tie equation counter to section counter
\renewcommand\theequation{\arabic{equation}\alph{section}}

\begin{document}
\refstepcounter{chapter} % just for this example

\section{Deflated Equilibrium}
$$a=b$$
\begin{align}
b=c \\
c=d
\end{align}

\section{Log-Lin Equilibrium}
$$a=b$$
\begin{align}
b=c \\
c=d
\end{align}

\end{document}

• You've stolen my proposition :-( – user31729 Feb 5 '17 at 10:45
• No! I was playing drama ;-) – user31729 Feb 5 '17 at 10:56
• @ChristianHupfer - :-) – Mico Feb 5 '17 at 11:03
• Thank you both for valuable help!! The only adjustment I had to made is to add \arabic{chapter}. to the \theequation command, such that the numbering is consistent with other chapters. – Chris tie Feb 5 '17 at 11:11
• @Mico: Well, 5 upvotes ;-) I would not have been awarded with this, although I had a similar idea. – user31729 Feb 5 '17 at 22:07