[Tex/LaTex] Doing maths with distance values in LaTeX source code

calculationsmacros

I have a sty file with the command

\newcommand{\foo}[1]{\noindent\kern#1}

but I'd actually like to have something like

\newcommand{\foo}[1]{\noindent\kern{#1 *0.5}}

meaning that I'd like to have half of the distance the user puts on command \foo to be passed to \kern. This obviously doesn't work.

Do you have any suggestions on how to do this?

(You may ask "why the hell would you want to do that??". Fair question. I'm using someone else's program which generates tex files and I don't have control over the values that come up on the command \foo. I just know that I'd like to have half of what that program chooses.)

Best Answer

Use the eTeX primitive \dimexpr to allow a factor like before dimension registers:

\newcommand{\foo}[1]{\noindent\kern .5\dimexpr#1\relax}

Note that \dimexpr swallows the \relax and also allows for some arithmetic inside. See the etex_manual for more details.

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[Tex/LaTex] How to define a new command based on \section with its optional argument

Quoting the UK TeX FAQ:

Optional arguments, in macros defined using \newcommand, don’t quite work like the optional argument to \section. The default value of \section’s optional argument is the value of the mandatory argument, but \newcommand requires that you ‘know’ the value of the default beforehand.

The requisite trick is to use a macro in the optional argument[...]

Using your MWE plus the first FAQ solution:

\documentclass{article}
\newcommand\mysec[2][\DefaultOpt]{%
  \def\DefaultOpt{#2}%
  \section[#1]{#2}%
}
\begin{document}
\tableofcontents
\mysec{Foo}
\mysec[Bla]{Bla bla bla}
\end{document}

enter image description here

[Tex/LaTex] Problem declaring newcommand with tikzpicture inside

You can use ampersand replacement; however, I'd not use the center environment, for better flexibility (and use \[...\] instead, around the command). You can also simplify the code using matrix of math nodes.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{matrix}

\newcommand{\SES}[3]{%
  \begin{tikzpicture}[every node/.style={midway},ampersand replacement=\&]
  \matrix [matrix of math nodes,column sep=2em, row sep=0em] at (0,0) {
  \node(A) {0} ;
  \& \node(B) {#1} ;
  \& \node(C) {#2} ;
  \& \node(D) {#3} ;
  \& \node(E) {0} ; \\};
  \draw[->] (A) -- (B)  node[anchor=south] {};
  \draw[->] (B) -- (C)  node[anchor=south] {};
  \draw[->] (C) -- (D)  node[anchor=south] {};
  \draw[->] (D) -- (E)  node[anchor=south] {};
  \end{tikzpicture}%
}

\begin{document}

\[
\SES{A}{B}{C}
\]

\end{document}

enter image description here

However, I'd recommend using tikz-cd.

\documentclass{article}
\usepackage{tikz-cd}

\newcommand{\SES}[3]{%
  \begin{tikzcd}[ampersand replacement=\&]
  0 \arrow[r] \& #1 \arrow[r] \& #2 \arrow[r] \& #3 \arrow[r] \& 0
  \end{tikzcd}%
}

\begin{document}

\[
\SES{A}{B}{C}
\]

\end{document}

enter image description here

With the simplified syntax of tikz-cd you'll probably give up to defining several types of commutative diagrams with macros.

Best Answer

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[Tex/LaTex] How to define a new command based on \section with its optional argument

[Tex/LaTex] Problem declaring newcommand with tikzpicture inside

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