4

I use the subequations and align environments as follows:

 \begin{subequations}
 \begin{align}
   \sum_{a \in \delta^+_G(v)} f^k_a -  \sum_{a \in \delta^-_G(v)} f^k_a  &= d^k_v, & \forall v \in V, k \in K \\ 
    \sum_{k \in K} f^k_a  &\le \sum_{m \in M}c^m x^m_a, & \forall a \in A   & \quad \texttt{Directed}\\
    \max \left\{\sum_{k \in K} \{f^k_{e+},f^k_{e-}\}  \right\}&\le \sum_{m \in M}c^m x^m_a, & \forall e \in E   & \quad \texttt{Bidirected}\\
    \sum_{k \in K} (f^k_{e+}+f^k_{e-})&\le \sum_{m \in M}c^m x^m_e, & \forall e \in E   & \quad \texttt{Undirected}
 \end{align}
 \end{subequations}

which shows the equations numbered as
1.a
1.b
1.c
1.d

However, I'd like the numbering to be displayed as
1
2.a
2.b
2.c

1
  • 1
    Welcome to TSE. Please post a Minimal Working Example, instead of a code snippet. Oct 24 at 10:28
5

I would like to suggest that you (a) embed all four statements in a gather environment and (b) embed the three inequalities in combined subequations and alignat environments. I would also recommend using \smashoperator directives in order to typeset the summation expressions in the first row more compactly.

enter image description here

\documentclass{article}
\usepackage{mathtools} % for \smashoperator macro

\begin{document}
\begin{gather}
   \smashoperator{\sum_{a \in \delta^+_G(v)}} f^k_a -  
   \smashoperator{\sum_{a \in \delta^-_G(v)}} f^k_a  = 
   d^k_v, \quad \forall v \in V,\ k \in K
\\[\jot]
\begin{subequations}
\begin{alignat}{3}
  \sum_{k \in K} f^k_a  
  &\le \sum_{m \in M}c^m x^m_a, 
  &\qquad& \forall a \in A   
  & \quad& \texttt{Directed} \\
  \max \biggl\{\sum_{k \in K} \{f^k_{e+},f^k_{e-}\}  \biggr\}
  &\le \sum_{m \in M}c^m x^m_a, 
  && \forall e \in E   
  && \texttt{Bidirected} \\
  \sum_{k \in K} (f^k_{e+}+f^k_{e-})
  &\le \sum_{m \in M}c^m x^m_e, 
  && \forall e \in E   
  &&  \texttt{Undirected}
\end{alignat}
\end{subequations}
\end{gather}
\end{document}
1
  • 2
    + Very good suggestion to use smash for the summation symbol. Personally I would use \tag for sub equations. Nice and simple. Oct 24 at 12:43
4

Mico just posted his answer as I was writing this, and you should consider that, but to directly answer the question with align I'd probably not use subequations and simply tag the later equations so

enter image description here

\documentclass{article}

\usepackage{amsmath}

\begin{document}

 \begin{align}
   \sum_{a \in \delta^+_G(v)} f^k_a -  \sum_{a \in \delta^-_G(v)} f^k_a  &= d^k_v, & \forall v \in V, k \in K \\ 
    \sum_{k \in K} f^k_a  &\le \sum_{m \in M}c^m x^m_a, & \forall a \in A   & \quad \texttt{Directed} \refstepcounter{equation}\tag{\theequation a}\\
    \max \left\{\sum_{k \in K} \{f^k_{e+},f^k_{e-}\}  \right\}&\le \sum_{m \in M}c^m x^m_a, & \forall e \in E   & \quad \texttt{Bidirected} \tag{\theequation b}\\
    \sum_{k \in K} (f^k_{e+}+f^k_{e-})&\le \sum_{m \in M}c^m x^m_e, & \forall e \in E   & \quad \texttt{Undirected}  \tag{\theequation c}
 \end{align}
\end{document}
1
4

You can define a new specialsubequations environment in which the first item is treated specially with the help of \specialequation.

\documentclass{article}
\usepackage{amsmath}
%\usepackage{hyperref} % not mandatory

\usepackage{lipsum} % for mock text, don't load it in your document

\makeatletter
\newcounter{specialsubequations}
\newenvironment{specialsubequations}
 {%
  \stepcounter{specialsubequations}%
  \stepcounter{equation}%
  \let\@currentlabel\theequation
  \label{@@@fake\thespecialsubequations @@@}%
  \subequations
 }
 {\endsubequations}
\@ifpackageloaded{hyperref}{%
  \newcommand{\specialequation}{\tag{\ref*{@@@fake\thespecialsubequations @@@}}}%
}{%
  \newcommand{\specialequation}{\tag{\ref{@@@fake\thespecialsubequations @@@}}}%
}
\makeatother

\begin{document}

\lipsum[1][1-3]
\begin{specialsubequations}
\begin{align}
  \sum_{a \in \delta^+_G(v)} f^k_a -  \sum_{a \in \delta^-_G(v)} f^k_a
  &= d^k_v, & \forall v \in V, k \in K \specialequation\label{1}
  \\ 
  \sum_{k \in K} f^k_a  &\le \sum_{m \in M}c^m x^m_a, 
  & \forall a \in A   & \quad \texttt{Directed}
  \\
  \max \left\{\sum_{k \in K} \{f^k_{e+},f^k_{e-}\}  \right\}
  &\le \sum_{m \in M}c^m x^m_a, & \forall e \in E   & \quad \texttt{Bidirected}
  \\
  \sum_{k \in K} (f^k_{e+}+f^k_{e-})&\le \sum_{m \in M}c^m x^m_e,
  & \forall e \in E   & \quad \texttt{Undirected}
\end{align}
\end{specialsubequations}
\lipsum[2][1-3]

\end{document}

You can add a \label to the special equation; links will work when hyperref is loaded.

enter image description here

However I'd recommend not changing the number.

\documentclass{article}
\usepackage{amsmath}
%\usepackage{hyperref} % not mandatory; use `\ref*` if hyperref is loaded

\usepackage{lipsum} % for mock text

\begin{document}

\lipsum[1][1-3]
\begin{subequations}\label{main}
\begin{align}
  \sum_{a \in \delta^+_G(v)} f^k_a -  \sum_{a \in \delta^-_G(v)} f^k_a
  &= d^k_v, & \forall v \in V, k \in K \tag{\ref{main}}
  \\ 
  \sum_{k \in K} f^k_a  &\le \sum_{m \in M}c^m x^m_a, 
  & \forall a \in A   & \quad \texttt{Directed}
  \\
  \max \left\{\sum_{k \in K} \{f^k_{e+},f^k_{e-}\}  \right\}
  &\le \sum_{m \in M}c^m x^m_a, & \forall e \in E   & \quad \texttt{Bidirected}
  \\
  \sum_{k \in K} (f^k_{e+}+f^k_{e-})&\le \sum_{m \in M}c^m x^m_e,
  & \forall e \in E   & \quad \texttt{Undirected}
\end{align}
\end{subequations}
\lipsum[2][1-3]

\end{document}

enter image description here

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