problem with align* and labels

Question

I have this code:

\begin{align*} \label{eq:svc2}
\stackrel{min}{\omega,b,\xi,\rho} \-\hspace{20pt} & \frac{1}{2}  \omega^T\omega - \nu \rho + \frac{1}{l} \sum_{i=1}^{l}{\xi_i} \\
\text{subject to} \-\hspace{20pt} & y_i(\omega^T\phi(x_i)+b) \geq \rho-\xi_i, \tag{eq:svc1}\\
& \xi_i \geq 0, i=1,...,l, \-\hspace{10pt} \rho \geq 0. \\
\end{align*}

I want to add a label for the entire equation, not one for each line.

How may I do it? I have tried \label nexto to \begin{align*} but a get an [warning: reference xxx on page xx undefined on input line xx] when referencing it using \ref

Answer 1

Perhaps you're thinking to aligned:

\documentclass{article}
\usepackage{amsmath}
\begin{document}


\begin{equation}\label{eq:svc2}
\begin{aligned}
\min_{\omega,b,\xi,\rho} \qquad &
  \frac{1}{2}  \omega^T\omega - \nu \rho + \frac{1}{l} \sum_{i=1}^{l}\xi_i \\
\textup{subject to} \qquad &
  y_i(\omega^T\phi(x_i)+b) \geq \rho-\xi_i,\\
  & \xi_i \geq 0, i=1,\dots,l, \quad \rho \geq 0.
\end{aligned}
\end{equation}

\end{document}

Note that \- makes no sense in math mode; also \min should be used and not \stackrel. For ... use \dots.