How to typeset aligned equations with a curly brace to the left and subnumbering

I want to typeset multiple equations that are

• aligned by the '=' sign
• are combined by a curly brace to the left
• have 'subnumbering'.

They should look like

{ a = b (1.1)a

{ c = d (1.1)b

{ e = f (1.1)c

where the '{'s represent one big curly brace to the left. I want to be able to refer to a specific subequation such as '(1.1)a', as well as to all of them by '(1.1)'.

I was able to construct equations with a curly brace, but they only have a common number, such as '(1.1)'. How to add the 'subnumbering'?

\documentclass{report}
\begin{document}
$$\left\{ \begin{array}{rcll} a & = & b \\ c & = & d \\ e & = & f \end{array} \right. \label{eq:test}$$
See equation \ref{eq:test}.
\end{document}


• please, provide mwe Aug 12, 2017 at 11:58
• for english-only speakers, "accolade" in this sense is a curly brace. Aug 12, 2017 at 12:34

\documentclass{report}
\usepackage{mathtools,cases}

\begin{document}
\begin{subequations}\label{eq:test}
\begin{numcases}{}
a = b &     \label{eq:1a}\\
c = d &     \label{eq:1b}\\
e = f &     \label{eq:1c}
\end{numcases}
See \eqref{eq:test} and more precisely \eqref{eq:1a}, \eqref{eq:1b} and \eqref{eq:1c}.
\end{subequations}
\end{document}


addendum. your second request can be easy fulfilled with empheq package or with following changes of above mwe:

\documentclass{report}
\usepackage{mathtools,cases}

\begin{document}
\begin{subequations}\label{eq:test}
\begin{numcases}{}
&\llap{aaa} = b       \label{eq:1a}\\
&\llap{c} = d      \label{eq:1b}\\
&\llap{e} = f       \label{eq:1c}
\end{numcases}
See \ref{eq:test} and more precisely \ref{eq:1a}, \ref{eq:1b} and \ref{eq:1c}.
\end{subequations}
\end{document}


• And you can add labels to each line of the numcases, as well as to a group of numcases? Aug 12, 2017 at 12:14
• @Karlo, see modified answer. Aug 12, 2017 at 14:15
• And how to align by '='? Aug 12, 2017 at 14:56
• with numcases is not so simply as with empheq, but see addendum to my answer. Aug 12, 2017 at 15:37

Another solution, with the empheq environment (needless to load amsmath: it loads mathtools, which loads it). It works with cleverref, and you can refer the equation as a whole, or the individual subsequations:

\documentclass{report}
\usepackage[utf8]{inputenc}
\usepackage{empheq}
\usepackage{cleveref}

\begin{document}

\begin{subequations}
\begin{empheq}[left=\empheqlbrace]{align}
a & = b[![enter image description here][1]][1] \\
c & = d\label{sseqb} \\
e & = f
\end{empheq}
\label{eq:test}
\end{subequations}
See \cref{eq:test} and more precisely \cref{sseqb}.

\end{document}


here is your answer but change the code slightly and put curly bracket in front of equations.

 \documentclass{article}
\usepackage{array}
\usepackage{amsmath}
\begin{document}

\begin{subequations}\label{first:main}

First some separate equations
$$a & = & b \label{first:1}$$

$$c & = & d \label{first:2}$$

$$e & = & f \label{first:3}$$
\end{subequations}

\end{document}