How to obtain same height of vwcol columns?

Question

I'm trying to use the vwcol package to put two sets of equations side-by-side. However, the equations in the right column are slightly higher than those on the left.

How can I set the height of both columns to be the same? Additionally, the equation numbers are Eqn. 7-12 - rather than 1-6 for some reason.

I also realise my question title isn't the best but I couldn't think of a more concise way of describing my issue. If anyone has a better suggestion, it would be greatly appreciated.

\documentclass[a4paper,11pt]{extarticle}
\usepackage[margin=0.80in]{geometry}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{vwcol}

\begin{document}

\begin{vwcol}[widths={0.3,0.7}, rule=0pt]
\begin{eqnarray}
\sigma_c &=& E_c \varepsilon_c 
\\
\sigma_{h\phi^+} &=& E_h \varepsilon_{h\phi^+} 
\\
\sigma_{h\phi^-} &=& E_h \varepsilon_{h\phi^-} 
\end{eqnarray}

\begin{eqnarray}
\varepsilon_c &=& \varepsilon_x 
\\
\varepsilon_{h\phi^+} &=& \varepsilon_y cos^2{\phi} + \varepsilon_x sin^2(\phi) + \gamma_{xy}sin(\phi)cos(\phi) 
\\
\varepsilon_{h\phi^-} &=& \varepsilon_y cos^2{\phi} + \varepsilon_x sin^2(\phi) - \gamma_{xy}sin(\phi)cos(\phi)
\end{eqnarray}
\end{vwcol} 

\end{document}

Answer 1

I don't know how to do it with vwcol, but it's easier with a couple of minipages.

\documentclass[a4paper,11pt]{extarticle}
\usepackage[margin=0.80in,showframe]{geometry}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{vwcol}

\begin{document}

\begin{center}
\setlength{\abovedisplayskip}{0pt}
\setlength{\belowdisplayskip}{0pt}
\begin{minipage}{.3\textwidth}
\begin{align}
\sigma_c &= E_c \varepsilon_c 
\\
\sigma_{h\phi^+} &= E_h \varepsilon_{h\phi^+} 
\\
\sigma_{h\phi^-} &= E_h \varepsilon_{h\phi^-} 
\end{align}
\end{minipage}% <--- Don't forget
\begin{minipage}{.7\textwidth}
\begin{align}
\varepsilon_c &= \varepsilon_x 
\\
\varepsilon_{h\phi^+} &= \varepsilon_y \cos^2\phi + \varepsilon_x \sin^2\phi + \gamma_{xy}\sin\phi\cos\phi 
\\
\varepsilon_{h\phi^-} &= \varepsilon_y \cos^2\phi + \varepsilon_x \sin^2\phi - \gamma_{xy}\sin\phi\cos\phi
\end{align}
\end{minipage}
\end{center}

\end{document}

The frame is due to the showframe option, used just for the example.

Never use eqnarray: the correct environment is align.

I changed, for consistency, all (\phi) into \phi.