# Number equations within array

I want to number sub-items of an array I have in order to refer to the right equation and not to the set of equations (SEE the pictures attached):

Figure that should call 1.35a, 1.35b, 135.c, 1.36a, 1.36b and 1.36c (and should have also sublabels):

.

Picture that should have sublabels:

I found two similar posts (like Subequations and Sub-numbering equations within array) but they don't apply and I couldn't implement in my example. I tried to replace my "equation" entries for subequations and label each line but it didn't work. What should I try?

An example of the array I have so far is (the example is for 1.34):

$$\left\{ \def\arraystretch{1.8} \begin{array}{l} \frac{\partial r}{\partial l} = \frac{-2r\cos\theta}{R_E\sin^3\theta} \left( \frac{r^2\sin^3\theta}{R_E(1+3\cos^2\theta)}\right) = \frac{-2r^3\cos\theta}{R_E(1+3\cos^2\theta)} \\ \frac{\partial r}{\partial q} = \frac{R^2_E\sin\theta}{r^2} \left( \frac{r^2\sin^3\theta}{R_E(1+3\cos^2\theta)}\right) = \frac{R_E\sin^4\theta}{(1+3\cos^2\theta)} \\ \frac{\partial r}{\partial \xi} = 0 \end{array} \right. \label{sc_parar}$$

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The following uses the idea from Sub-numbering equations within array and the cases package:

\documentclass{article}
\usepackage{cases}% http://ctan.org/pkg/cases
\renewcommand{\theequation}{\thesection.\arabic{equation}}
\renewcommand{\thesubequation}{\themainequation\alph{equation}}
\newcommand{\pderiv}[2]{\frac{\partial #1}{\partial #2}}
\begin{document}

\section{Some stuff}

\setcounter{equation}{27}
$$\left\{\begin{array}{@{}r@{}l@{}} \displaystyle\pderiv{x}{\zeta} & {}= \mbox{(\ref{A}) and (\ref{X})} \\ \displaystyle\pderiv{y}{\zeta} & {}= \mbox{(\ref{B}) and (\ref{Y})} \\ \displaystyle\pderiv{z}{\zeta} & {}= \mbox{(\ref{C}) and (\ref{Z})} \end{array}\right.$$

\setcounter{equation}{33}

\begin{subnumcases}{}
\pderiv{r}{l}     = A \label{A} \\
\pderiv{r}{q}     = B \label{B} \\
\pderiv{r}{\zeta} = C \label{C}
\end{subnumcases}

And then some text.
\begin{subnumcases}{}
\pderiv{\theta}{l}     = X \label{X} \\
\pderiv{\theta}{q}     = Y \label{Y} \\
\pderiv{\theta}{\zeta} = Z \label{Z}
\end{subnumcases}

\end{document}


Here is a duplicate implementation using empheq:

\documentclass{article}
\renewcommand{\theequation}{\thesection.\arabic{equation}}
\newcommand{\pderiv}[2]{\frac{\partial #1}{\partial #2}}
\begin{document}

\section{Some stuff}

\setcounter{equation}{27}
$$\left\{\begin{array}{@{}r@{}l@{}} \displaystyle\pderiv{x}{\zeta} & {}= \mbox{(\ref{A}) and (\ref{X})} \\ \displaystyle\pderiv{y}{\zeta} & {}= \mbox{(\ref{B}) and (\ref{Y})} \\ \displaystyle\pderiv{z}{\zeta} & {}= \mbox{(\ref{C}) and (\ref{Z})} \end{array}\right.$$

\setcounter{equation}{33}

\begin{subequations}
\begin{empheq}[left=\empheqlbrace]{align}
\pderiv{r}{l}     &= A \label{A} \\
\pderiv{r}{q}     &= B \label{B} \\
\pderiv{r}{\zeta} &= C \label{C}
\end{empheq}
\end{subequations}

And then some text.
\begin{subequations}
\begin{empheq}[left=\empheqlbrace]{align}
\pderiv{\theta}{l}     &= X \label{X} \\
\pderiv{\theta}{q}     &= Y \label{Y} \\
\pderiv{\theta}{\zeta} &= Z \label{Z}
\end{empheq}
\end{subequations}

\end{document}

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Is this what you're trying to do?

\begin{subequations}\label{group}
\begin{align}
\frac{\partial r}{\partial l} = \frac{-2r\cos\theta}{R_E\sin^3\theta} \left( \frac{r^2\sin^3\theta}{R_E(1+3\cos^2\theta)}\right) = \frac{-2r^3\cos\theta}{R_E(1+3\cos^2\theta)}\label{first} \\
\frac{\partial r}{\partial q} =  \frac{R^2_E\sin\theta}{r^2} \left( \frac{r^2\sin^3\theta}{R_E(1+3\cos^2\theta)}\right) = \frac{R_E\sin^4\theta}{(1+3\cos^2\theta)}\label{second} \\
\frac{\partial r}{\partial \xi} = 0 \label{third}
\end{align}
\end{subequations}


You can then refer to the entire group using something like \eqref{group} or one of the subequations using \eqref{first}. There is a good example in the Short Math Guide to LaTeX.

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yes, I'm trying to mantain the braquet in the entire group and even a label to refer later... but I need also a label for each equation in the array – Claudia Nov 17 '13 at 20:48