Arithmetic in arguments to the geometry package

Question

I'd like to use the geometry package to auto-crop the output of my LaTeX (so that it looks bigger on-screen as I'm editing). I have found a way to remove the margins completely and brutally:

\geometry{paperwidth=\textwidth,  paperheight = \textheight, margin=0cm}

However, I'd like to be somewhat more gentle. I tried the following, but it does not work:

\geometry{paperwidth=\textwidth + 1cm,  paperheight = \textheight+1cm, margin=1cm}

The reason is that arithmetic does not work inside these arguments. (LaTeX doesn't seem smart enough to do the addition).

What is the correct way to achieve this effect?

Answer 1

It works if you load the calc package.

\documentclass{article}

\usepackage{calc}

\usepackage{geometry}

\geometry{paperwidth=\textwidth+1cm,paperheight=\textheight+1cm, margin=1cm}

\usepackage{lipsum}

\begin{document}

\lipsum[1]

\end{document}

Answer 2

\dimexpr allows for expression-like addition/subtraction of dimensions:

\usepackage{geometry}% http://ctan.org/pkg/geometry
\geometry{
  paperwidth=\dimexpr\textwidth + 1cm\relax,
  paperheight=\dimexpr\textheight+1cm\relax, 
  margin=1cm}

calc automates this process through a redefinition of the length/dimension-related macro (\setlength, \addtolength, etc.).

Answer 3

\dimexpr...\relax is not flexible enough because you cannot do division by a floating point number. \dimexpr\textwidth/3.141592654\relax, for example, is not possible!

That is why I prefer using the fp package because it can do any calculation.

\documentclass{article}
\usepackage[nomessages]{fp}

\FPeval{Width}{round(pow(0.5,2)*10*sin(pi/2):3)}% $10\sqrt(2)$ in 3 digits
%     after decimal point
\FPeval{Height}{round(pow(0.5,3)*10+cos(pi/2):3)}% $10\sqrt(3)$ in 3 digits
%    after decimal point

\usepackage
[
    paperwidth=\Width cm,
    paperheight=\Height cm,
]
{geometry}

\usepackage{lipsum}

\begin{document}

\lipsum[1]

\end{document}