[Tex/LaTex] Proper way to use \ensuremath to define a macro useable in and out of math mode

macrosmath-mode

Based on this solution related to defining a macro I came up with this macro to help me define a macro that I can use either in or outside of math mode.

The example as is functions as I want. However, this solution requires me to NOT put $$ around the second parameter to to the \DefineNamedFunction macro. I would like to be able to include the $$, or not include it.

One solution is to modify \DefineNamedFunction to strip out the $$ if it is included in the macro call using the xstring pacakge, but this to me feels like a hack, and am thinking that there is probably a cleaner TeX way to do this.

So to summarize: How do I change \DefineNamedFunction such that I can use both the commented and uncommented calls to this macro, and still be able to use the definition inside and outside of math mode?

\documentclass{article}

\usepackage{amsmath}
\usepackage{xcolor}

\newcommand{\DefineNamedFunction}[2]{% {FunctionName}{FunctionExpression}
    \expandafter\providecommand\expandafter{\csname#1\endcsname}{\textcolor{red}{\ensuremath{#2}}}%
}

\begin{document}

\DefineNamedFunction{FunctionF}{y = 2 \sin x}
%\DefineNamedFunction{FunctionF}{$y = 2 \sin x$}

I can use FunctionF inside math mode as $\FunctionF$,
but can also use this outside of math mode as \FunctionF.

\end{document}

Best Answer

Probably

\ensuremath{\textcolor{red}{#2}}

is what you need, since \textcolor can be used in text and in math. The complete definition is

\newcommand{\DefineNamedFunction}[2]{% {FunctionName}{FunctionExpression}
    \expandafter\providecommand\csname#1\endcsname
      {\ensuremath{\textcolor{red}{#2}}}%
}
...
\DefineNamedFunction{FunctionF}{y=2\sin x}
$\FunctionF$ and \FunctionF

Sample

I've also deleted the braces that require another \expandafter, but that's not the problem.

Of course, you can't call

\DefinedNamedFunction{FunctionFF}{$y=x$}

and I wouldn't know why you'd want it. But in any case there's a simple solution

\newcommand{\DefineNamedFunction}[2]{%
  \expandafter\providecommand\csname#1\endcsname
    {\ensuremath{\begingroup\color{red}\DNFnorm#2\endgroup}}}
\makeatletter
\def\DNFnorm{\@ifnextchar$\DNFnormi{}}
\def\DNFnormi$#1${#1}
\makeatother

The input is "normalized" by removing the $ tokens before and after, if present.

With \begingroup\color{red}...\endgroup the spaces in the subformula participate to the stretching and shrinking of the spaces in the line.

Related Solutions

[Tex/LaTex] Macro for \left( and \right)

without using amsmath:

\documentclass{article}
\begingroup
  \catcode`(\active \xdef({\left\string(}  % ( is defined as \left(
  \catcode`)\active \xdef){\right\string)} % ) is defined as \right)
\endgroup
\mathcode`(="8000 \mathcode`)="8000        % active in mathmode

\begin{document}
\[ 
   (\frac{(3-\frac{1}{x})^2}{(\frac4x-1)x}) 
\]    
\end{document}

enter image description here

and if you are using package amsmath

\documentclass{article}
\usepackage{amsmath}
\makeatletter
\def\resetMathstrut@{%
  \setbox\z@\hbox{%
    \mathchardef\@tempa\mathcode`\[\relax
    \def\@tempb##1"##2##3{\the\textfont"##3\char"}%
    \expandafter\@tempb\meaning\@tempa \relax
  }%
  \ht\Mathstrutbox@\ht\z@ \dp\Mathstrutbox@\dp\z@}
\makeatother
\begingroup
  \catcode`(\active \xdef({\left\string(}
  \catcode`)\active \xdef){\right\string)}
\endgroup
\mathcode`(="8000 \mathcode`)="8000
\begin{document}

\begin{align}
 f(x) &= (\frac{(3-\frac{1}{x})^2}{(\frac4x-1)x}-1)x^2 
\end{align}

\end{document}

enter image description here

[Tex/LaTex] When not to use \ensuremath for math macro

Two objections come to mind:

If you don't know you will be entering math mode, then you may write something "semantically" correct that breaks.

For example:

\documentclass{article}
\newcommand\mathmacro[1][A]{\ensuremath{{#1}_1}}
\begin{document}
 \mathmacro[$x^2$] % The dollar signs *leave* math mode
\end{document}

What's going on here is that \mathmacro[$x^2$] expands to

\ensuremath{{$x^2$}_1}

which expands to (effectively)

\ifmmode
 {$x^2$}_1
\else
 ${$x^2$}_1$
\fi

and you can see that if you write it outside of math mode, the second branch is taken, so the first dollar sign brings you into math mode and the one at the front of $x^2$ takes you out of it, with the reverse operation happening afterwards. This gives an error.

Of course, you aren't supposed to do that, since \mathmacro is actually a "math macro usable in text mode", so you should think of the thing between the brackets of its argument as being in math mode. Alas, this confuses both the author and the text editor's syntax highlighting, since it is a nonstandard assumption.

Edit: I would define this macro as:

\newcommand\mathmacro[1][A]{{#1}_1}

and use it as:

$x^2$ sub one: $\mathmacro[x^2]$.

This way, the parts that are math are clearly math.

In the unlikely event that you or some package sets \everymath, you will be very surprised when your apparently text-mode macros start to look different.

On the subject of semantics, though, the issue is clear: \ensuremath breaks the separation between math and text, which are two very different things. TeX even has the distinction built in: different fonts, different spacing rules, different parsing rules. You can probably construct a lot more counterexamples by exploiting these.

What I mean by this is that in the following situation:

\documentclass{article}
\newcommand\mathmacro[1][A]{\ensuremath{{#1}_1}}
\begin{document}
 A sub one: \mathmacro

 \bfseries A sub one: \mathmacro
\end{document}

you may be surprised that the bold text does not extend to the contents of the apparently text-mode \mathmacro.

What I'm saying is not so much that \ensuremath actually breaks anything as that it violates your expectations to the point that it makes things harder rather than easier.

Best Answer

Related Solutions

[Tex/LaTex] Macro for \left( and \right)

[Tex/LaTex] When not to use \ensuremath for math macro

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