# [Tex/LaTex] using subequations

amsmathequationserrors

I have an equation consisting of two parts and would like to use subequation for that.
Here's the code:

\usepackage{amsmath}

\begin{subequations}
$$\operatorname{min}_{a,b,c} \frac{1}{2}\mathbf{w}^{T}\mathbf{w} + C \sum_{i=1}^{l}\xi_{i}$$
$$y_{i}\left(\mathbf{w}^{T}\phi(x_{i})+b\right)$$

\end{subequations}


I'm getting an error:

final.tex:118:Missing $inserted. final.tex:118:Display math should end with$\$.


Can anybody help with that?

Paragraph breaks (which are produced by empty lines, too) don't quite work in math mode. Once you remove the empty line, the code compiles fine:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\begin{subequations}
$$\operatorname{min}_{a,b,c} \frac{1}{2}\mathbf{w}^{T}\mathbf{w} + C \sum_{i=1}^{l}\xi_{i}$$
$$y_{i}\left(\mathbf{w}^{T}\phi(x_{i})+b\right)$$
\end{subequations}

\end{document}