Math & Science ⇒ Subequations within Align/Gather environment

[davidnsibs]

Hello,

I'm trying to have the situation as below:

my first equation ... (1)
my second equation .. (2)
my third equation ... (3a)
my fourth equation .. (3b)
my fifth equation ... (4)

and would like these all in the same align environment so as to not require the need to manually remove whitespace.

Obviously one 'solution' is
\begin{align}
first equation\\
second equation
\end{align}
\begin{subequations}
\begin{align}
third equation\\
fourth equation
\end{align}
\end{subequations}
\begin{align}
fifth equation
\end{align}

but as mentioned, this is not desirable as the whitespace would need to be played around with. Is there a known way to include subequations inside align tags?

Many thanks

[frabjous]

I'd probably define some commands of my own, perhaps something like this?

Code: Select all

\documentclass{article}
\usepackage{amsmath}
\newcounter{subeq}
\renewcommand{\thesubeq}{\theequation\alph{subeq}}
\newcommand{\newsubeqblock}{\setcounter{subeq}{0}\refstepcounter{equation}}
\newcommand{\mysubeq}{\refstepcounter{subeq}\tag{\thesubeq}}

\begin{document}
\begin{align}
1+1&=2\\
2+2&=4\\
\newsubeqblock
\mysubeq 3+3&=6 \\
\mysubeq 3+3&=4+2  \\
4+4&= 8
\end{align}
\end{document}

subeq.png (2.88 KiB) Viewed 8660 times

[davidnsibs]

That is fantastic, thank you!

[koala102938]

Yes, this is very good! Thank you, frabjous!

How can you label a complete subeqblock? Something like the following (that doesn't work):

\begin{document}
\begin{align}
1+1&=2\\
2+2&=4\\
\newsubeqblock\label{eq:block}
\mysubeq 3+3&=6 \\
\mysubeq 3+3&=4+2 \\
4+4&= 8
\end{align}
\end{document}

This is reference to a complete subeqblock \eqref{eq:block}