breqn override dgroup number

Question

Is there a way to override the base number in breqn's dgroup environment? Take the following example:

\documentclass{article}
\usepackage{breqn}

\begin{document}

\begin{dgroup}[number={2}]
  \begin{dmath}
    a=b
  \end{dmath}
  \begin{dmath}
    c=d
  \end{dmath}
\end{dgroup}

\end{document}

this produces something like

a=b   (0a)
c=d   (0b)

Instead, I'd like

a=b   (2a)
c=d   (2b)

I know I can achieve the same effect with

\begin{dgroup}
  \begin{dmath}[number={2a}]
    a=b
  \end{dmath}
  \begin{dmath}[number={2a}]
    c=d
  \end{dmath}
\end{dgroup}

But I'd rather not have to do that.

Answer 1

I'm not sure if this is the best solution (and doesn't override a dgroup parameter as implied in the question), but you can set the equation counter directly. For instance,

\setcounter{equation}{1}
\begin{dgroup}
  \begin{dmath}
    a=b
  \end{dmath}
  \begin{dmath}
    c=d
  \end{dmath}
\end{dgroup}

produces the desired result. Presumably, dgroup uses and increments the equation counter which is why this yields the numbering (2a) and (2b).