%% 
%%  Example 01-03-7 
%%  Copyright (C) 2017 Herbert Voss
%% 
%% ==== 
% Show page(s) 1
%% 
%% 
\documentclass[]{screxa}
\pagestyle{empty}
\setlength\textwidth{328.62788pt}
\setlength\parindent{0pt}
%StartShownPreambleCommands
\usepackage{amsmath}
\makeatletter
%Roman counter
\newcounter{roem} \renewcommand\theroem{\roman{roem}}
% save the original counter
\newcommand\c@org@eq{}  \let\c@org@eq\c@equation
\newcommand\org@theeq{} \let\org@theeq\theequation
%\setroem sets roman counting
\newcommand\setroem{\let\c@equation\c@roem \let\theequation\theroem}
%\setarab the arabic counting
\newcommand\setarab{\let\c@equation\c@org@eq \let\theequation\org@theeq}
\makeatother
%StopShownPreambleCommands
\begin{document}
\begin{align}
f(x) &= \int\sin x\,\mathrm{d}x\label{eq:arab1}\\  g(x) &= \int\frac{1}{x}\,\mathrm{d}x
\end{align}
%
\setroem
\begin{align}
F(x) &=-\cos x          \\   G(x) &=\ln x\label{eq:rom1}
\end{align}
%
\setarab
\begin{align}
f^{\prime} (x) &= \sin x\\  g^{\prime} (x) &= \frac{1}{x}\label{eq:arab2}
\end{align}
There can be references to these equations in the usual way, like eq.\ref{eq:arab1},
\ref{eq:arab2} and for the roman one eq.\ref{eq:rom1}.
\end{document}
