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I have several large TikZ plots I want to externalize. Without externalization, everything works fine.

Document:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{external}
%\tikzexternalize
\begin{document}
  \input{plot}
\end{document}

Output:

$ pdflatex article
<output omitted>
(./plot.tex) [1{/var/lib/texmf/fonts/map/pdftex/updmap/pdftex.map}]
(./article.aux) )</usr/share/texlive/texmf-dist/fonts/type1/public/amsfonts/cm/
cmr10.pfb>
Output written on article.pdf (1 page, 357026 bytes).
Transcript written on article.log.

However, when I uncomment \tikzexternalize, pdflatex exists with an error.

$ pdflatex article
<output omitted>
(./plot.tex
Runaway text?
[x=1pt,y=1pt] \definecolor {fillColor}{RGB}{255,255,255} \path [use a\ETC.
! TeX capacity exceeded, sorry [main memory size=5000000].
<argument> ... circle ( 1.16); \par \path [dr\ETC.

l.21034 \end{tikzpicture}

!  ==> Fatal error occurred, no output PDF file produced!
Transcript written on article.log.

What is going on here? How can externalization increase space consumption? After all, the whole point of externalization is to improve efficiency and space consumption during compilation.

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  • Not a TikZ expert, but I'm pretty sure when you use \tikzexternalize you need to enable shell escaping (pdflatex -shell-escape article). If that doesn't work you will need to show us the plot.tex file or a stripped down version which fails with the same error. Commented May 16, 2019 at 1:12
  • @PhelypeOleinik -shell-escape is not the problem here, but: Activating externalization significantly increases space consumption. Please find plot.tex here. Commented May 16, 2019 at 1:24
  • Seems line you got the TeX code from a drawing tool like inkscape. Any reason you do not just compile the thing in a standalone class and just include the resulting graphics?
    – user121799
    Commented May 16, 2019 at 1:41
  • @marmot Reasons: no need to compile each plot manually, maintaining consistency in terms of font family etc. is simpler... Of course, it would be a possible workaround. However, I'm interested in understanding what the problem is here. It makes no sense to me that activating externalization significantly increases space consumption. After all, again, externalization is all about improving efficiency and space consumption. Commented May 16, 2019 at 2:01
  • OK, in this case you may be interested in section 6.1 Memory Limits of TEX of the pgfplots (!) manual. (BTW, I sometimes indeed write a "wrapper" standalone file that loads the same relevant styles and compile pdf's with those. I agree that this is more efforts if you use the plots, say, in regular notes and in beamer document, so +1.)
    – user121799
    Commented May 16, 2019 at 2:11

2 Answers 2

2

What you say is correct: the point of externalisation is to reduce resource usage. However every optimisation has some overhead. To externalise a picture TikZ reads the contents of the entire tikzpicture environment and passes that to an external run of the engine to produce the picture. The externalisation library passes around the contents of the picture in macros in order to set everything up to make the picture and this ends up creating more than one copy of the same thing.

When you compile the document the error message asks Runaway text? and tells you that you filled up TeX's memory.

Your plot.tex file is 1.1 MB, and TeX's main memory size is 5000000 “words of memory”, or 2.5 MB, so it takes a little over two copies of the contents of the file to run out of space.

The solution? Use TeX's macros and TikZ's styles to reduce the size of the input while maintaining the result of the code. For example, your file has 10269 (!) instances of

\path[draw=drawColor,line width= 0.4pt,line join=round,line cap=round]

If you do

\tikzset{mydots/.style={draw=drawColor,line width= 0.4pt}}
%,line join=round,line cap=round <-- These two don't do anything here anyway

and then replace all other occurrences of that option list by mydots you'll reduce the file size to 500 kB (which is enough to make it work).

You can go further and define a macro

\def\circ(#1,#2){\path[mydots](#1,#2)circle(1.16);}

and then replace all the

\path [mydots] ( something, another) circle (1.16);

by

\circ(something,another)

which will bring the file size down to 200 kB.

It can be further optimized using TikZ's magic, but I'll leave it as an exercise for the reader ;)

Here's the 200 kB file for you: https://pastebin.com/rJfe4ctx

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  • 2
    I morally agree with you, so +1, but not with the "details". How much sense do line join=round,line cap=round in \path[draw=drawColor,line width= 0.4pt,line join=round,line cap=round] ( 32.86, 41.56) circle ( 1.16); make? Rather than defining styles for these I would just kick out all unnecessary stuff, which will reduce the memory load and the computation time. ;-)
    – user121799
    Commented May 16, 2019 at 2:26
  • @marmot Oh, agreed. I didn't even look at the “does it make sense?” part, I just made it work. I dare say there is a way to chain all those circles in a single path instruction to avoid the overhead of starting and ending a path each time. However it was way past bedtime, so I left it as “exercise for the reader”. Thanks for the nudge, though :-) Commented May 16, 2019 at 10:14
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If the document is stable and you will make few modifications to tikzpicture, it is better to handle it in separate files and include them as an image (or with input).... ltximg script you can do the following:

$ ltximg --subenv --imgdir=mypics --prefix=tkz -o test-out test-in.tex

Now you will have a document with the tikzpicture environments converted into images (preserving the consistency of the fonts) and you will also have each tikzpictureenvironment in separate files (in case you need some extra modification). First check the documentation to see the options and conditions that the input file must meet.

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