[Tex/LaTex] Numbering an array as one single equation LaTeX

arraysnumbering

I've looked around at various sites and tried switching between array/eqnarray but don't seem to be able to get the effect I would like. I want to simply give an array I have one single equation number. I would also like to know just to make sure, how to give each equation a number within an array.

The equation I have is the following:

$$
\begin{array}{lr}
N_{x,sk} = k_{sk}\left(\frac{t_{sk}}{b_{sk}}\right)^{2}\bar{Et} \;\;
N_{x,st} = k_{st}\left(\frac{t_{st}}{b_{st}}\right)^{2}\bar{Et}
\end{array}
$$

Could someone please help provide examples where I would have these equations showing one equation number and then also an example with two separate ones please?

Best Answer

Using the eqnarray environment instead of array, you can add \nonumber to any lines you don't want numbered. If you don't do this, every line will be numbered.

\begin{eqnarray}
N_{x,sk} &=& k_{sk}\left(\frac{t_{sk}}{b_{sk}}\right)^{2}\bar{Et} \nonumber \\
N_{x,st} &=& k_{st}\left(\frac{t_{st}}{b_{st}}\right)^{2}\bar{Et}
\end{eqnarray}

(Just remove the \nonumber from the above to get the second example.)

Related Solutions

[Tex/LaTex] array environment with tags/labels

A solution that uses alignat:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{alignat}{2}
&T &&= x + y \\
&T_{\text{total}} &&= y
\end{alignat}
\end{document}

[Tex/LaTex] Number equations within array

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

enter image description here

\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}
\begin{equation}
  \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.
\end{equation}

\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:

enter image description here

\documentclass{article}
\usepackage{empheq}% http://ctan.org/pkg/empheq (autoloads amsmath)
\renewcommand{\theequation}{\thesection.\arabic{equation}}
\newcommand{\pderiv}[2]{\frac{\partial #1}{\partial #2}}
\begin{document}

\section{Some stuff}

\setcounter{equation}{27}
\begin{equation}
  \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.
\end{equation}

\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}

Best Answer

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