# [OS X TeX] Working right with subequations

Sam Cox samcox2 at mac.com
Tue Jan 2 13:47:07 EST 2007

On Jan 2, 2007, at 1:30 PM, Christian Burk wrote:

> Hallo,
>
> I would like to use the subequations feature of amsmath.
>
> I have an equation environment with \label{eq:1} and this equation
> is numbered with 0.1.
> Afterwards I have the subequations environment consisting of two
> equations with \label{eq:1A} and \label{eq:1B}, but these two
> equations are numbered 0.2a and 0.2b.
>
> How could I achieve that the equations with the label 1A and 1B get
> the number 0.1a and 0.1b?

There may be a better way but this works.  Use \addtocounter{equation}
{-1} after the equation and before the subequation.  Here it is:

\documentclass[a4paper,12pt,chapterprefix,abstracton]{scrreprt}
\usepackage{amsmath}

\begin{document}

$$\label{eq:1} \underline{M} \ \underline{\ddot{u}} + \underline{C} \ \underline{\dot {u}} + \underline{S} \ \underline{u} = \underline{f}$$
\begin{subequations}
\begin{align}
u &= \left(\begin{array}{c}u_1 \\ \vdots \\ u_k \\ \vdots \\ u_N
\end{array}\right) \label{eq:1A} \\
u &= \left(\begin{array}{c}u_2 \\ \vdots \\ u_k \\ \vdots \\ u_N
\end{array}\right) \label{eq:1B}
\end{align}
\end{subequations}

\end{document}

Sam