Conflict with tikzexternalize

Question

I've created matrices with some diagonal lines and some tweaking on \vdots. (based on these posts: diagonal line within matrix and How to vertically center the \vdots in this node? )

The result is exactly what I want, but when I copy the code from my test/trial&error file to my main file I encounter a problem. After some searching I've located the issue: without the tikzexternal command everything works fine.

However, my main file is rather large so I cant really go without the tikzexternal command.

Can someone fix this for me? (and explain what the problem is?) Just uncomment the 3 tikzexternalize lines to reproduce the error.

(maybe relevant: with the tikzexternalize enabled I get different errors in each document, let me know if you need the actual error messages)

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}

%\usepgfplotslibrary{external} %use with --shell-escape
%\tikzexternalize[prefix=Tikzplots/]
%\pgfplotsset{compat=newest}

\makeatletter               %vdots without extra space on top
\DeclareRobustCommand{\rvdots}{%
    \vbox{
        \baselineskip4\p@\lineskiplimit\z@
        \kern-\p@
        \hbox{.}\hbox{.}\hbox{.}
}}
\makeatother


\newcommand\tikzmark[1]{%       %nodes in matrix for lines
    \tikz[overlay,remember picture,baseline] \node [anchor=base] (#1) {};}

\newcommand\MyLine[3][]{%       %draw lines between the nodes^
    \begin{tikzpicture}[overlay,remember picture]
    \draw[#1] (#2.north west) -- (#3.east);
    \end{tikzpicture}}



\begin{document}

\[
\begin{bmatrix}
Y[1]\\
\phantom{0}\\
\rvdots\\
\rvdots\\
\phantom{0}\\
Y[k]
\end{bmatrix}
=
\begin{bmatrix}
\phantom{0}\tikzmark{a} & \phantom{0}& \phantom{0}& \phantom{0}&\phantom{0}& \phantom{0} \\
\\
\\
\\
\\
& & & & & \tikzmark{b}\phantom{0}
\end{bmatrix}
\cdot
\begin{bmatrix}
X[1]\\
\phantom{0}\\
\rvdots\\
\rvdots\\
\phantom{0}\\
X[k]
\end{bmatrix}
\]



\[
\begin{bmatrix}
Y[1]\\
\phantom{0}\\
\rvdots\\
\rvdots\\
\phantom{0}\\
Y[k]
\end{bmatrix}
=
\begin{bmatrix}
\phantom{0}\tikzmark{c} & \phantom{0} &\phantom{0}\tikzmark{e} &\phantom{0} & \phantom{0}\tikzmark{g}& \phantom{0}\\
& & & & &\tikzmark{h}\phantom{0}\\
\phantom{0}\tikzmark{i}& & & & &\\
& & & & & \tikzmark{f}\phantom{0} \\
\phantom{0}\tikzmark{k}& & & & &\\
&\tikzmark{l}\phantom{0} & &\tikzmark{j}\phantom{0} & & \tikzmark{d}\phantom{0}\\
\end{bmatrix}
\cdot
\begin{bmatrix}
X[1]\\
\phantom{0}\\
\rvdots\\
\rvdots\\
\phantom{0}\\
X[k]
\end{bmatrix}
\] 
\MyLine[thick]{a}{b}
\MyLine[red,thick]{c}{d}
\MyLine[thick]{e}{f}
\MyLine[thick]{g}{h}
\MyLine[thick]{i}{j}
\MyLine[thick]{k}{l}
\end{document}

Answer 1

If one adds \tikzexternaldisable and tikzexternalenable at the appropriate places (and adds the missing pgfplots-package) it works fine for me:

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{pgfplots}

\usepgfplotslibrary{external} %use with --shell-escape
\tikzexternalize[prefix=Tikzplots/]
\pgfplotsset{compat=newest}

\makeatletter               %vdots without extra space on top
\DeclareRobustCommand{\rvdots}{%
    \vbox{
        \baselineskip4\p@\lineskiplimit\z@
        \kern-\p@
        \hbox{.}\hbox{.}\hbox{.}
}}
\makeatother


\newcommand\tikzmark[1]{%       %nodes in matrix for lines
    \tikzexternaldisable\tikz[overlay,remember picture,baseline] \node [anchor=base] (#1) {};\tikzexternalenable}

\newcommand\MyLine[3][]{%       %draw lines between the nodes^
    \tikzexternaldisable
    \begin{tikzpicture}[overlay,remember picture]
    \draw[#1] (#2.north west) -- (#3.east);
    \end{tikzpicture}\tikzexternalenable}



\begin{document}

\[
\begin{bmatrix}
Y[1]\\
\phantom{0}\\
\rvdots\\
\rvdots\\
\phantom{0}\\
Y[k]
\end{bmatrix}
=
\begin{bmatrix}
\phantom{0}\tikzmark{a} & \phantom{0}& \phantom{0}& \phantom{0}&\phantom{0}& \phantom{0} \\
\\
\\
\\
\\
& & & & & \tikzmark{b}\phantom{0}
\end{bmatrix}
\cdot
\begin{bmatrix}
X[1]\\
\phantom{0}\\
\rvdots\\
\rvdots\\
\phantom{0}\\
X[k]
\end{bmatrix}
\]



\[
\begin{bmatrix}
Y[1]\\
\phantom{0}\\
\rvdots\\
\rvdots\\
\phantom{0}\\
Y[k]
\end{bmatrix}
=
\begin{bmatrix}
\phantom{0}\tikzmark{c} & \phantom{0} &\phantom{0}\tikzmark{e} &\phantom{0} & \phantom{0}\tikzmark{g}& \phantom{0}\\
& & & & &\tikzmark{h}\phantom{0}\\
\phantom{0}\tikzmark{i}& & & & &\\
& & & & & \tikzmark{f}\phantom{0} \\
\phantom{0}\tikzmark{k}& & & & &\\
&\tikzmark{l}\phantom{0} & &\tikzmark{j}\phantom{0} & & \tikzmark{d}\phantom{0}\\
\end{bmatrix}
\cdot
\begin{bmatrix}
X[1]\\
\phantom{0}\\
\rvdots\\
\rvdots\\
\phantom{0}\\
X[k]
\end{bmatrix}
\] 
\MyLine[thick]{a}{b}
\MyLine[red,thick]{c}{d}
\MyLine[thick]{e}{f}
\MyLine[thick]{g}{h}
\MyLine[thick]{i}{j}
\MyLine[thick]{k}{l}
\end{document}