General ⇒ Definition of a Macro involving Counters

[leo simon]

Hi,

I've defined the macro \linkedLabels below to give me linked equation numbers

What I've done works ok, but there are two problems with it
1) I'd like to define \newcounter inside the macro, rather than separately in the preamble, but it appears that newcounter has to be in the preamble
2) It's silly to have arguments #2 and #3 be separate since obviously #3 is determined by #2. However, the command \tag{\the#2$\empty_\text{#4}$} doesn't work. Nor does \tag{\value{#2} etc}

So to summarize, my questions are:
1) is there away to define counters in the body of the document
2) is there a way in a macro to reference the value of a counter whose name is passed to the macro as an argument?

Thanks very much for any help!!

The code below includes the macro and illustrates the way I want to use it.

Code: Select all

\documentclass{amsart}%
\usepackage{ifthen}
\def\linkedLabels#1#2#3#4{\ifthenelse{#1=1}
    {\addtocounter{equation}{1}
     \setcounter{#2}{\theequation}}{}
     \label{eq:#2-#4}
     \tag{#3$\empty_\text{#4}$}}
\newcounter{tmpCounter}
\begin{document}
\begin{align}
a = b
\end{align}
\begin{align}
\linkedLabels{1}{tmpCounter}{\thetmpCounter}{sym}
a = b
\end{align}
\begin{align}
a = b
\end{align}
\begin{align}
\linkedLabels{2}{tmpCounter}{\thetmpCounter}{sb}
a = b
\end{align}
Referring to equations \eqref{eq:tmpCounter-sym} and \eqref{eq:tmpCounter-sb}, we find
\end{document}

[kaiserkarl13]

Perhaps I'm not answering your question, but does this do what you desire?

Code: Select all

\documentclass{amsart}%
\begin{document}
\begin{align}
  a = b
\end{align}
\refstepcounter{equation}%
\label{eq:tmpCounter}%
\begin{align}
  a = b \tag{\ref{eq:tmpCounter}$_\text{sym}$}
  \label{eq:tmpCounter-sym}
\end{align}
\begin{align}
  a = b
\end{align}
\begin{align}
  \stepcounter{equation}
  a = b \tag{\ref{eq:tmpCounter}$_\text{sb}$}
  \label{eq:tmpCounter-sb}
\end{align}
Referring to equations \eqref{eq:tmpCounter-sym} and \eqref{eq:tmpCounter-sb}, we find
\end{document}

[cgnieder]

I'm not sure I understand exactly what you want the command to do. I assume the following:

1. a switch which lets the command either use the next equation number or the one when the command was last used
2. make a label with a custom name
3. add a subscript to the equation number

Maybe you can clarify that?

If my assumption is right I would probably do something like this:

Code: Select all

\documentclass{amsart}

\makeatletter
\newif\if@nextequation
\@nextequationfalse

\newcounter{mylabel}

\newcommand*\mylabel{%
  \@ifstar
   {\@nextequationfalse\my@label@i}
   {\@nextequationtrue\my@label@i}}

\newcommand*\my@label@i[2]{%
  \label{eq:#1-#2}%
  \if@nextequation
   \stepcounter{equation}%
   \setcounter{mylabel}{\value{equation}}%
  \fi
  \tag{\arabic{mylabel}$_\text{#2}$}}
\makeatother

\begin{document}
\begin{align}
 a = b
\end{align}
\begin{align}
 a = b \mylabel{name}{sym}
\end{align}
\begin{align}
 a = b
\end{align}
\begin{align}
 a = b \mylabel*{name}{sb}
\end{align}
\begin{align}
a = b
\end{align}
Referring to equations \eqref{eq:name-sym} and \eqref{eq:name-sb}, we find
\end{document}

To answer your questions:

1. counters can be defined in the document body without problems

   Code: Select all

   \documentclass{article}
   \begin{document}
   \newcounter{example}
   \setcounter{example}{3}
   \theexample
   \end{document}

2. yes, there is:

   Code: Select all

   \documentclass{article}
   \newcounter{example}
   \setcounter{example}{3}
   \makeatletter
   \newcommand\showcounter[1]{%
     the counter \texttt{#1} has the value \@nameuse{the#1}}
   \makeatother
   \newcommand\ShowCounter[1]{%
     the counter \texttt{#1} has the value \arabic{#1}}
   \begin{document}
   \showcounter{example}; \ShowCounter{example}
   
   \setcounter{example}{7}
   \showcounter{example}; \ShowCounter{example}
   \end{document}

Regards

[leo simon]

Thanks to both of you for suggestions.
- \refstepcounter will be very useful, I've always wanted to be able to define a label outside of an environment. It would be nice if there were a command that did nothing but redefine the default counter used by \label. I.e., does exactly what \refstepcounter does but doesn't increment the argument of refstepcounter

- \@nameuse{the#2} solves the bigger of my problems!

- It turns out that what I need to do is to define a counter inside of a macro, as in

Code: Select all

\def\tmpCounter#1#2{
       \newcounter{#1}
       \setcounter{#1}{#2}
        etc

But this doesn't seem to work

[cgnieder]

Although it's generally not a good idea to define a new counter inside a command it is possible.

And one could define a \refcounter which doesn't increment the counter but makes it available for \label.

Code: Select all

\documentclass{article}
\makeatletter
\newcommand*\refcounter[1]{%
  \protected@edef\@currentlabel{\csname p@#1\endcsname\csname the#1\endcsname}}
\makeatother
\begin{document}
\makeatletter
\newcommand*\tmpCounter[2]{%
  \@ifundefined{c@#1}
    {\newcounter{#1}%
     \setcounter{#1}{#2}}
    {\setcounter{#1}{#2}}}
\makeatother

\tmpCounter{test}{3}
\thetest % 3

\tmpCounter{test}{5}
\thetest % 5

\refcounter{test}\label{show_me}
\ref{show_me} % 5
\end{document}