The subequations environment provided by AMS-LaTeX changes the numbering style of the equations inside it to (4.9a) (4.9b) (4.9c) etc. if the preceding numbered equation was (4.8).
Example[]
\begin{subequations}\label{lorenz}
\begin{align}
\dot x &= \sigma(y-x) \label{l1} \\
\dot y &= x(\rho-z) - y \label{l2} \\
\dot z &= xy - \beta z \label{l3}
\end{align}
\end{subequations}
Other numbering schemes[]
Using standard LaTeX commands for counters, you can redefine \theequation to use Roman numerals:
\renewcommand{\theequation}{\theparentequation \roman{equation}}
Preamble[]
To use subequations, import the amsmath package with \usepackage{amsmath} in your preamble.
See also[]
- \eqref (for making cross-references to equations)