# Multi-page equation with only a single equation number

I understand that environments such as equation would not allow page break while align will.

But I want an equation box that only comes with one equation number and it spans over multiple pages. How do I do that?

• \allowdisplaybreaks in preamble combined with eg multline or gather+ aligned environments. – JPi Oct 29 '15 at 7:05

A solution with a new environment, where you just specify the line where you want the equation number:

\documentclass{article}

\usepackage[a6paper,textheight=4cm]{geometry} % just for the example
\usepackage{amsmath}
\allowdisplaybreaks

\makeatletter
\newcounter{longaligned}
\newenvironment{longaligned}[1][]
{%
\stepcounter{longaligned}%
\refstepcounter{equation}%
\label{longaligned@\thelongaligned}%
#1%
\start@align\@ne\st@rredtrue\m@ne % start align*
}
{\endalign}
\newcommand{\longalignedtag}{\tag{\ref{longaligned@\thelongaligned}}}
\makeatother

\begin{document}

\begin{longaligned}
a &=b \\
c &= a+b \\
d &= h+u+j+k \\
r +e &= t + e+ r + r\\
a &=b \\
c &= a+b \\
d &= h+u+j+k \\
r +e &= t + e+ r + r\longalignedtag\\
a &=b \\
c &= a+b \\
d &= h+u+j+k \\
r +e &= t + e+ r + r
\end{longaligned}

\end{document}


It's easy to manually adjust the position of one command, than using several \notag commands; the disadvantage is that this requires two steps for synchronization, but it shouldn't be a real problem.

A different solution based on the same idea:

\documentclass{article}

\usepackage[a6paper,textheight=4cm]{geometry} % just for the example
\usepackage{amsmath}
\allowdisplaybreaks

\makeatletter
\newcounter{longaligned}
\newenvironment{longaligned}
{%
\stepcounter{longaligned}%
\refstepcounter{equation}%
\label{longaligned@\thelongaligned}%
#1%
\par\textbf{Equation block \eqref{longaligned@\thelongaligned}}
\start@align\@ne\st@rredtrue\m@ne % start align*
}
{\endalign}
\makeatother

\begin{document}

\begin{longaligned}
a &=b \\
c &= a+b \\
d &= h+u+j+k \\
r +e &= t + e+ r + r\\
a &=b \\
c &= a+b \\
d &= h+u+j+k \\
r +e &= t + e+ r + r\\
a &=b \\
c &= a+b \\
d &= h+u+j+k \\
r +e &= t + e+ r + r
\end{longaligned}

\end{document}


If you prefer, you can easily add “End of equation block” at the bottom.

In both cases, calling the environment as

\begin{longaligned}[\label{xyz}]


will allow to use \eqref{xyz} for referring to the block.

You can use lot of \notag s:

\documentclass{article}
\usepackage{amsmath}
\setlength{\textheight}{4cm}  %% just for this example
\allowdisplaybreaks
\begin{document}
\begin{align}
a &=b \notag\\
c &= a+b \notag\\
d &= h+u+j+k \notag\\
r +e &= t + e+ r + r\notag\\
a &=b \notag\\
c &= a+b \notag\\
d &= h+u+j+k \notag\\
r +e &= t + e+ r + r\\
a &=b \notag\\
c &= a+b \notag\\
d &= h+u+j+k \notag\\
r +e &= t + e+ r + r\notag
\end{align}
\end{document}


But this is not a good idea to have many equations spanning more than one page with one equation number. Have some mercy on the readers.

• It's for derivations that spans for more than a page. It wouldn't be appropriate to assign multiple equation numbers. And I am writing a report, where I am instructed to give a number to each and whatever equation block. – Argyll Oct 29 '15 at 8:16
• Btw, if align is the solution, why not use align* and apply a single label? – Argyll Oct 29 '15 at 8:17
• @Argyll: You can use anything appropriate. Mine was a blind shot as I had no idea of the nature of the equation/s. With align*, you have to step up the equation counter yourself. – user11232 Oct 29 '15 at 8:18
• Or just use align* and a suitably crafted \tag. Exercise for the reader. ;-) – egreg Oct 29 '15 at 8:46