[Tex/LaTex] Cross reference to align

Question

What I want to do is to make a cross reference to program (P) and still be able to make cross references to each separate line in the alignment.

\begin{align}
  (P)\quad \min &cx\label{objective}\\
  s.t.: & Ax\geq b\label{firstConst}\\
        & Dx\geq d\label{secondConst}\\
        & x\in\{0,1\}\label{binary}
 \end{aling}

I known that I can use gather-aligned to make a reference to the program, but then I do not have the possibility to make references to separate lines. Any suggestions?

Answer 1

You could use subequations to number the individual contraints, and tag the whole program with P. At least that is something I've seen in some books:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\begin{equation}
  a = b
\end{equation}

\renewcommand{\theequation}{P}
\begin{subequations}\label{ip}
\renewcommand{\theequation}{\theparentequation.\arabic{equation}}
\begin{align}
  \min &\ cx\label{objective}\\
  \text{s.t.}\qquad Ax & \geq b\label{firstConst}\\
        Dx & \geq d\label{secondConst}\\
        x  & \in\{0,1\}\label{binary}
 \end{align}
\end{subequations}
\renewcommand{\theequation}{\arabic{equation}}
The binary program~\eqref{ip}, the objective~\eqref{objective}, the constraint~\eqref{firstConst}.

\begin{equation}
  c = d
\end{equation}
\end{document}