Array equation numbering misplaced

Question

I have a couple of equations from Autometrics which I want numbered but for some reason, the equation numbering always goes on the line below the equation. I would want the numbering to be somewhere in the middle of the equation or next to the last line of the equation. Below is the code for one of the equations. Thanks

\documentclass[12pt, varwidth, border=10pt]{article}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage[onehalfspacing]{setspace}
\usepackage{geometry}
\usepackage[final]{graphicx}

\begin{document}

\begin{equation}
  \begin{array}{lcl}
  r_{p,t} & = &
  \begin{array}[t]{r} 
  0.0043
  \\ ^{(0.003)}
  \end{array}
  \ -\!\begin{array}[t]{r}
  0.0068
 \\ ^{(0.0019)}
 \end{array}
 D_{1}
 \ -\!\begin{array}[t]{r}
 0.0053
 \\ ^{(0.0023)}
 \end{array}
 D_{2}
 \ -\!\begin{array}[t]{r}
 0.0036
 \\ ^{(0.0021)}
 \end{array}
  D_{3}
  \ -\!\begin{array}[t]{r}
  0.00026
  \\ ^{(0.0020)}
  \end{array}
  D_{4}
  \ +\!\begin{array}[t]{r}
  0.31
  \\ ^{(0.066)}
  \end{array}
   R_{Mt}
  \\ & &
  \ +\!\begin{array}[t]{r}
 0.026
 \\ ^{(0.0016)}
 \end{array}
 \text{S}_{\text{13-Dec}}
 \ -\!\begin{array}[t]{r}
  0.026
  \\ ^{(0.0030)}
  \end{array}
  \text{S}_{\text{16-Dec}}
  \end{array} 
  \end{equation} 

\end{document}

Answer 1

I can suggest a few improvements, one of which is to use \begin{array}[t]{@{}r@{}}. The other is to reduce the distance between the number and the accuracy; finally split is a lot easier.

A macro for easing input is also recommended.

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage[onehalfspacing]{setspace}
\usepackage{geometry}

\newcommand{\numprec}[2]{%
  \begingroup\renewcommand{\arraystretch}{0.5}%
  \begin{array}[t]{@{}r@{}} #1 \\ \scriptstyle (#2) \end{array}%
  \endgroup
}

\begin{document}

\begin{equation}
\begin{split}
  r_{p,t} &=
  \numprec{0.0043}{0.003}
 -\numprec{0.0068}{0.0019} \, D_{1}
 -\numprec{0.0053}{0.0023} \, D_{2}
 -\numprec{0.0036}{0.0021} \, D_{3}
 -\numprec{0.00026}{0.0020} \, D_{4}
 +\numprec{0.31}{0.066} \, R_{Mt}
\\
 &\qquad
 +\numprec{0.026}{0.0016} \, \mathrm{S}_{\text{13-Dec}}
 -\numprec{0.026}{0.0030} \, \mathrm{S}_{\text{16-Dec}}
\end{split}
\end{equation} 

\end{document}

In case the first row doesn't fit, you can move the last summand to the next line.

If you remove the \qquad, you get

Answer 2

If you remove the padding from the arrays with @{} you can use normal spacing around =, -, + and then I'd use an AMS multi line display rather than an outer array.

\documentclass{article}

\usepackage{amsmath}
\begin{document}

\begin{multline}
  r_{p,t}  = 
  \begin{array}[t]{@{}r@{}} 
  0.0043
  \\ ^{(0.003)}
  \end{array}
  -\begin{array}[t]{@{}r@{}}
  0.0068
 \\ ^{(0.0019)}
 \end{array}
 D_{1}
 -\begin{array}[t]{@{}r@{}}
 0.0053
 \\ ^{(0.0023)}
 \end{array}
 D_{2}
 -\begin{array}[t]{@{}r@{}}
 0.0036
 \\ ^{(0.0021)}
 \end{array}
  D_{3}
  -\begin{array}[t]{@{}r@{}}
  0.00026
  \\ ^{(0.0020)}
  \end{array}
  D_{4}
  +\begin{array}[t]{@{}r@{}}
  0.31
  \\ ^{(0.066)}
  \end{array}
   R_{Mt}
\\
  +\begin{array}[t]{@{}r@{}}
 0.026
 \\ ^{(0.0016)}
 \end{array}
 \text{S}_{\text{13-Dec}}
 -\begin{array}[t]{@{}r@{}}
  0.026
  \\ ^{(0.0030)}
  \end{array}
  \text{S}_{\text{16-Dec}}
  \end{multline}
\end{document}