Page Layout ⇒ Arithmetical operations in space definitions

[theo moore]

Hi, I define certain spaces in my document like so,

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\newcommand{\leftsize}{0.75\textwidth}
\newcommand{\cellsize}{0.15\textwidth}

I'd like to form a new value which is like,

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\newcommand{\prodsize}{\cellsize*\leftsize}

(Or perhaps I may want to subtract one from the other). Unfortunately, this does not seem to work, i.e. I have to manually code in,

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\newcommand{\prodsize}{0.1125\textwidth}

Is there a better solution?

[gmedina]

Hi,

to do simple arithmetical operations on the arguments of commands, you could use the calc package.

[theo moore]

The calc package doesn't seem to like the command

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\newcommand{\prodsize}{\leftsize*\cellsize}

Any idea why? It does okay with things like,

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\newcommand{\prodsize}{\leftsize*\real{0.5}}

but not when I use two variables.

[gmedina]

Can you please post your definitions for \leftsize and \cellsize?

[theo moore]

Can you please post your definitions for \leftsize and \cellsize?

They're in the first post.

[gmedina]

Sorry about that.

Anyway, the problem comes from both \leftsize and \cellsize having a unit (pt, in this case). One possible solution is to use the \strip@pt LaTeX macro to get rid of the unit and then perform the multiplication:

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\documentclass{article}
\usepackage{calc}

\newlength\leftsize
\addtolength\leftsize{0.75\textwidth}
\newlength\cellsize
\addtolength\cellsize{0.15\textwidth}
\newlength\prodsize

\makeatletter
  \newcommand\mylen{\strip@pt\cellsize}
\makeatother

\addtolength\prodsize{\leftsize*\real{\mylen}}

\begin{document}

\the\leftsize

\the\cellsize

\the\prodsize

\end{document}

[Stefan Kottwitz]

Hi Theo,

• I would not multiply macros, I recommend to use TeX lengths instead, because you are dealing with length values.
• What do you expect as result of 0.75\textwidth*0.15\textwidth? That's not a length, it's an area.

Try this example:

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\documentclass[a4paper,10pt]{article}
\usepackage{calc}
\newlength{\leftsize}
\setlength{\leftsize}{0.75\textwidth}
\newlength{\cellsize}
\setlength{\cellsize}{0.15\textwidth}
\newlength{\addsize}
\setlength{\addsize}{\leftsize+\cellsize}
\newlength{\prodsize}
\newcommand*\factor{0.5}
\setlength{\prodsize}{\factor\cellsize}

\begin{document}
\rule{\leftsize}{1ex}

\rule{\cellsize}{1ex}

\rule{\addsize}{1ex}

\rule{\prodsize}{1ex}
\end{document}

Stefan