I have numerous equations within an align environment which I want to have numbered as EqNa, EqNb, ..... I cut and pasted a solution I found for the equation environment and it does what I want numbering wise but it errors out and I cannot figure out why. Any suggestions greatly appreciated.

I assume fixing the error will result in the final equation being correctly numbered 5 also. Thanks

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

\newcounter{defcounter}
\setcounter{defcounter}{0}
\newenvironment{myequation}{%
\addtocounter{equation}{-1}
\refstepcounter{defcounter}
\renewcommand\theequation{D\thedefcounter}
\begin{equation}}
{\end{equation}}

\begin{equation}
y = a x + b
\end{equation}

\begin{myequation}
y = \alpha x + \beta
\end{myequation}
\newcounter{eqNumHold}\setcounter{eqNumHold}{0}
\newcounter{subEq}\setcounter{subEq}{0}

\newenvironment{myalign}{%
\setcounter{subEq}{0}
\refstepcounter{equation}
\setcounter{eqNumHold}{\value{equation}}
\refstepcounter{subEq}
\renewcommand\theequation{%
\theeqNumHold\alph{subEq}%
\addtocounter{equation}{-1}}
\begin{align}}
{\setcounter{equation}{\value{eqNumHold}}\end{align}}

\begin{align}
y_1 & = a_1 x + b_1 \\
y_2 & = a_2 x + b_2
\end{align}

\begin{myalign}
y_1 & = \alpha_1 x + \beta_1 \\
y_2 & = \alpha_2 + \beta_2
\end{myalign}

$$ E = mc^2 $$
\end{document}

Am Tue, 1 Jun 2021 07:53:11 -0700 (PDT) schrieb Dave94705:

> but it errors out and I cannot figure out why. Any
> suggestions greatly appreciated.

Use \align/\endalign

\newenvironment{myalign}{%
\setcounter{subEq}{0}
\refstepcounter{equation}
\setcounter{eqNumHold}{\value{equation}}
\refstepcounter{subEq}
\renewcommand\theequation{%
\theeqNumHold\alph{subEq}%
\addtocounter{equation}{-1}}
\align}
{\setcounter{equation}{\value{eqNumHold}}\endalign}

--
Ulrike Fischer
http://www.troubleshooting-tex.de/