[Tex/LaTex] Creating a new environment with referencing

cross-referencingenvironmentshyperref

I'm trying to create a referenceable "system" environment that basically displays an equation with a custom counter. Then I want to reference the environment with autoref, so as to have "System (S1)" as output when I reference it.

\newcounter{system}\setcounter{system}{0}

\newenvironment{system}{\refstepcounter{system}\begin{equation*}}{\hfill(S\arabic{system})
\end{equation*}}

\hyperref[system]{System~\ref{system}}
\def\systemautorefname{System}

\begin{system}
 \dot x=u(x),
\label{s1}
\end{system}

However, when I do

\autoref{s1}

I get an error saying that the reference s1 is undefined. What am I missing?

Best Answer

Some remarks:

The label has used the name s1, the references system. The label name must match, the example below uses s1.
The use equation* indicates that probably package amsmath is used.
With amsmath \tag can be used to print the equation number.
Redefining \p@system helps to get the parentheses around the number, when it is referenced.
I have put \label outside environment equation with the name as option to the environment system to avoid trouble with the redefinition of \label inside environments of amsmath.
The star form of \ref avoids the link inside a link in the line with \hyperref.

Example:

\documentclass{article}
\usepackage{amsmath}
\usepackage{hyperref}

\newcounter{system}
\renewcommand*{\thesystem}{S\arabic{system}}
\newcommand*{\systemautorefname}{System}
\makeatletter
\renewcommand*{\p@system}{%
  \expandafter\p@@system
}
\newcommand*{\p@@system}[1]{%
  (#1)%
}
\makeatother

\newenvironment{system}[1][]{%
  \refstepcounter{system}%
  \ifx\\#1\\%
  \else
    \label{#1}%
  \fi
  \begin{equation}%
}{%
  \tag{\thesystem}%
  \end{equation}%
}

\begin{document}

\hyperref[s1]{System~\ref*{s1}}, \autoref{s1}

\begin{system}[s1]
 \dot x=u(x),
\end{system}

\end{document}

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enter image description here

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\end{myproofs}

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Here I put the proof that $2+2=4$.
\end{myproofs}

\end{document}

Best Answer

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