number several equations with only one number

Question

How can I number several equations in a align environment using only one number?

For example

\\begin{align}
w^T x_i + b \\geqslant 1-\\xi_i \\text{ if }         


        

Answer 1

How about something like:

\documentclass{article}

\usepackage{amssymb,amsmath}

\begin{document}

\begin{equation}\label{A_Label}
  \begin{split}
    w^T x_i + b \geqslant 1-\xi_i \text{ if } y_i &= 1, \\
    w^T x_i + b \leqslant -1+\xi_i \text{ if } y_i &= -1
  \end{split}
\end{equation}

\end{document}

which produces: