[Tex/LaTex] Detect whether running on pdfTeX or Knuth’s TeX for conditional include

macrospdftexplain-tex

Does anyone know a way to detect whether one is running in pdfTeX or Knuth's TeX? I want to be able to conditionally include extra features when a document is being built using pdfTex, but also support original TeX as a fallback.

Something like

\ifdefined\pdfpagewidth
\pdfpagewidth 8.5 true in
\pdfpageheight 11 true in
\fi

would get the job done — however the above relies on the e-TeX extensions and doesn't build on Knuth TeX.

Thanks

Best Answer

Something like this?

Since \csname foo\endcsname expands to \relax if \foo is not defined, it's possible use \ifx.... to compare the command sequence to be equal to \relax. This does not need e-TeX at all.

\newif\ifknuthtex
\expandafter\ifx\csname pdfpagewidth\endcsname\relax
\knuthtextrue
\else
\pdfpagewidth 8.5 true in
\pdfpageheight 11 true in
\fi

This is \ifknuthtex Knuth's \TeX\else pdfTeX\fi
\bye

Compiling with tex gives the image below.

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See documentation of pdfTeX (pdftex-a.pdf). You can use e.g. \pdfmapfile in you document. Or to quote the documentation:

If you want to use a base map file name other than pdftex.map, or change its processing options through a pdfTeX format, you can do this by appending the \pdfmapfile command to the \everyjob{} token list for the -ini run, e. g.: \everyjob\expandafter{\the\everyjob\pdfmapfile{+myspecial.map}} \dump This would always read the file myspecial.map after the default pdftex.map file.

[Tex/LaTex] auto-detect conditional probabilities in macro

This can differentiate the argument as you requested.

\documentclass{article}
\def\P(#1){\Phelper#1|\relax\Pchoice(#1)}
\def\Phelper#1|#2\relax{\ifx\relax#2\relax\def\Pchoice{\Pone}\else\def\Pchoice{\Ptwo}\fi}
\def\Pone(#1){\Pr\left( #1 \right)}
\def\Ptwo(#1|#2){\Pr\left( #1 \mid #2 \right)}
\def\Pr{\mathbf{Pr}}
\begin{document}
$\P(A)$ or $\P(A|B)$
\end{document}

enter image description here

If your arguments are always short, then a simpler \def\P(#1){\Pr(#1)} may be sufficient for your need. But since you are using \left(...\right), it might be the case that you want to handle tall arguments. In that case, I would replace \mid with \,\middle|\, so that you could achieve the following, which works in both text style and display style:

\documentclass{article}
\def\P(#1){\Phelper#1|\relax\Pchoice(#1)}
\def\Phelper#1|#2\relax{\ifx\relax#2\relax\def\Pchoice{\Pone}\else\def\Pchoice{\Ptwo}\fi}
\def\Pone(#1){\Pr\left( #1 \right)}
\def\Ptwo(#1|#2){\Pr\left( #1 \,\middle|\, #2 \right)}
\def\Pr{\mathbf{Pr}}
\begin{document}
\centering$\P(A)$ or $\P(A|B)$

\[\P(\displaystyle\frac{x}{2}>1 | x>0) = 0.5\]
\end{document}

enter image description here

Best Answer

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