# Tikzmath, ERROR: Missing \endcsname inserted

I'm trying to use tikzmath to draw lines between a set of points, however I've an error ERROR: Missing \endcsname inserted. on the line \ni=\i+1;. Any idea why?

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{math,calc}

\begin{document}

\begin{tikzpicture}
\tikzmath{
\n=5;
}
\foreach \i in {-\n,...,\n} {
\foreach \j in {-\n,...,\n} {
\node[circle,fill,inner sep=1pt] at ($(\i+.3*\j,.5*\j)$) (n-\i-\j) {};
}
}
\foreach \i in {-\n,...,\n-1} {
\foreach \j in {-\n,...,\n-1} {
\tikzmath{%
\ni=\i+1;
\nj=\j+1;
};
\draw[] (n-\i-\j) -- (n-\i-\nj);
}
}
\end{tikzpicture}
\end{document}

• I suspect the problem is that \ni is defined to be a number in TeX’s eyes (it’s defined with \mathchardef). If I change \ni to \nx, I don't get the error, but other ones due to wrong code. – egreg Apr 19 at 9:39
• Addition to @egreg's comment the wrong code is the last \n-1 parts in the foreach list. TikZ doesn't evaluate the expressions there. You might add \numexpr before it. – percusse Apr 19 at 9:42

Due to how \tikzmath works, you can’t use variable names that correspond to already defined commands that point to mathematical symbols.

The standard definition of \ni is by \mathchardef\ni="3233 (in a glorified form in fontmath.ltx) and TeX considers \mathchardef tokens as numbers when it’s looking for them.

The same error happens, for instance, if I use \propto instead of \ni.

Use another name.

With other fixes, as suggested by percusse:

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{math,calc}

\begin{document}
\pagestyle{empty}

\begin{tikzpicture}
\tikzmath{
\n=5;
}
\foreach \i in {-\n,...,\n} {
\foreach \j in {-\n,...,\n} {
\node[circle,fill,inner sep=1pt] at ($(\i+.3*\j,.5*\j)$) (\n-\i-\j) {};
}
}
\foreach \i in {-\n,...,\numexpr\n-1} {
\foreach \j in {-\n,...,\numexpr\n-1} {
\tikzmath{%
\nni=\i+1;
\nj=\j+1;
};
\draw[] (\n-\i-\j) -- (\n-\i-\nj);
}
}
\end{tikzpicture}
\end{document}

• You could also do \let\ni\undefined at the start of the tikzpicture. – egreg Apr 19 at 10:12
\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{math,calc}
\usepackage{verbatim}

\begin{document}
\pagestyle{empty}

\begin{tikzpicture}
\def\n{5}
\foreach \i in {-\n,...,\n} {
\foreach \j in {-\n,...,\n} {
\node[circle,inner sep=1pt] at ($(\i+.3*\j,.5*\j)$) (n-\i-\j) {};
}
}
\foreach \i [evaluate=\i as \ni using int(\i+1)] in {-\n,...,\numexpr\n-1} {
\foreach \j [evaluate=\j as \nj using int(\j+1)] in {-\n,...,\numexpr\n-1} {
\draw (n-\i-\j) -- (n-\ni-\nj);
}
}
\end{tikzpicture}
\end{document}