align multiple equations without amsmath package

Question

I have to use iopart document class. One of major problems which I came across is aligning multiple equations. For example, for reach

\begin{align}
  a & = b \label{eq1} \\
    c & = d \label{eq2}
\end{align}

we must use either amsmath package or other ones. Unfortunately, iopart does not coincide with it. In this situation how can I align my equations that have gotten me to stack?

Answer 1

You can use \usepackage{IEEEtrantools} to align multiple equations without to use amsmath package.

\documentclass[a4paper,12pt]{article}
\usepackage{IEEEtrantools}
\begin{document}
\begin{IEEEeqnarray}{lCr}
 a & = b \label{eq1} \\
c & = d \label{eq2}
\end{IEEEeqnarray}
\end{document}

Answer 2

You can use the package witharrows which provides an environment DispWithArrows which has by default exactly the same behaviour as the environment align of amsmath.

\documentclass{iopart}
\usepackage{witharrows}
\begin{document}
\begin{DispWithArrows}
  a & = b \label{eq1} \\
    c & = d \label{eq2}
\end{DispWithArrows}
\end{document}

With DispWithArrows, you have the ability to add arrows on the right for explanations (hence the name):

\documentclass{iopart}
\usepackage{witharrows}
\begin{document}
\begin{DispWithArrows}
  a & = b \Arrow{explanation} \label{eq1} \\
    c & = d \label{eq2}
\end{DispWithArrows}
\end{document}

Answer 3

With mathenv (good old) package which significantly improve eqnarray environment (package is based on mdwtab's table handling macros).

\documentclass[a4paper,12pt]{article}
\usepackage{mathenv}

\begin{document}
    \begin{eqnarray}[rl]
a   & = b \label{eq1} \\
c   & = d \label{eq2}
    \end{eqnarray}
\end{document}