How to NOT render a part of a document

Question

I would like to use an environment that makes everything inside... invisible! I would like that during the .tex compilation to read everything but not render some parts of my LaTeX document.

The problem of \begin{comment} ... Is that the code inside is not "read". I know my problem is unusual, but in fact I want the code inside to be read (it will generate a file), but I don't want it to be rendered (it normally write lines and lines of codes I don't want)

The problem of \phantom is that it is still "rendered" as a blank rectangle. If I do that I have a huge blank space

(In fact, I want to use SageTex, which "mix" SageMath and LaTeX. There is a way to write a sage code directly in the .tex file. You have to compile with LaTeX the document. It will produce a .sage document, that I have to compile with sage this time. Finally, I have to compile with LaTeX so that the Sage calculations are "understood" by LaTeX. For example I can write a sage code "x = 2 + 2", and use $\sage{x}$, it will render 4. But my problem is that by doing that, it always render first verbatim "x = 2 + 2". And I don't want to see that. I want my calculations to be hidden, not rendered, such that, at viewing the .pdf we can't determine if sage was used or not)

Simple example :

\usepackage{sagetex}
\begin{document}
%\begin{comment}
\begin{sageblock}
U = 12
\end{sageblock}
%\end{comment}
U = $\sage{U}$
\end{document}

I want a simple render "U = 12" in a "LaTeX way". With this I have it two times. Once in a "sage code way", and once the well-rendered "LaTeX way"

The solution of StefanH :

\newcommand\donotshow[1]{\smash{\vphantom{#1}}}

Seems to work well, but I still have an error. I think it's because I don't want to use only \donotshow{something} but \donotshow{ an environment, with multiple lines}

Answer 1

Use the sagesilent environment instead of sageblock. According to the sagetex manual,

this environment is like sageblock, but it does not typeset any of the code; it just writes it to the .sage file. This is useful if you have to do some setup in Sage that is not interesting or relevant to the document you are writing.

Answer 2

The comment package provides an environment comment to remove parts of the code from the output:

\documentclass{article}
\usepackage{comment}

\begin{document}
This text will be output.
\begin{comment}
And that won't.
\end{comment}
\end{document}

which results in

This text will be output.

Answer 3

Maybe not the nicest solution, but you can use \vphantom to get a box of no horizontal space and the same vertical distance as the content, then removing it with \smash.

\documentclass{article}
\usepackage[nopar]{lipsum}
\newcommand\testA{\textbf{AAA}}
\newcommand\donotshow[1]{\smash{\vphantom{#1}}}
\begin{document}
\testA
\lipsum[1]
\textbf{[HERE]}
\donotshow{%
  Test of renewing commands
  \gdef\testA{\textbf{BBB}}
}%
\lipsum[2]
\testA
\end{document}

At the point of [HERE] some text is vanished together with a redefinition of \testA. I use \gdef since, to my knowledge, there is no global version of \renewcommand.

Answer 4

You can make small parts of text or math vanish by using \phantom (standard TeX). For larger parts you can make the text transparent, using \transparent{0} from the transparent package. The vanished parts are just invisible, but will still occupy space.

\documentclass{article}
\usepackage{transparent}
\newcommand\somestuff
  {Some sample text different from lipsum.
   \begin{equation}
     x = 1 + \phantom{2} + 3
   \end{equation}
   Some sample \phantom{text} different from lipsum.
  }
\begin{document}
\somestuff

{\transparent{0}%
\somestuff

}
\somestuff
\end{document}