Computing in the list of a tikz foreach

Question

If I say something along the lines of

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\def\I{2}
\foreach \i in { \I+1, ..., 20 }
  \node at (\i,10) {+};
\end{tikzpicture}
\end{document}

I get the message

! Illegal unit of measure (pt inserted).
<to be read again> 
                   +
l.560     \node[anchor=center] at (\i,10) {$+$};

How can I do arithmetic in the bounds of a foreach ... range?

While code snippets are useful in explanations, it is always best to compose a fully compilable MWE that illustrates the problem including the \documentclass and the appropriate packages so that those trying to help don't have to recreate it. — Peter Grill, Nov 30 '11 at 20:15

score 17 · Accepted Answer · answered Nov 30 '11 at 20:34

17

Some possibilities with foreach. In your case, you can try the first one

\documentclass[11pt]{scrartcl}
\usepackage{tikz}


\begin{document} 
  \def\I{2}   
\begin{tikzpicture}
\foreach \i   [evaluate=\i] in {\I+1,...+1,19+1}
  \node[anchor=center] at (\i,0) {$\i$};
\end{tikzpicture} 

\begin{tikzpicture}
\foreach \i   [evaluate=\i as \j using \i+1] in {\I,...,10}
  \node[anchor=center] at (\j,0) {$\j$};
\end{tikzpicture} 

\begin{tikzpicture}
\foreach \i   [evaluate=\i as \j using \i*\i] in {\I,...,4}
  \node[anchor=center] at (\j,0) {$\j$};
\end{tikzpicture}   
\end{document}

answered Nov 30 '11 at 20:34

Alain Matthes

95,075

2

I would have never thought of ... + 1 :) – Mariano Suárez-Álvarez Nov 30 '11 at 20:46
This one is minimally disruptive, so far. – Mariano Suárez-Álvarez Nov 30 '11 at 21:00
1

Hi Alain, how can I do this with non integer steps? I have tried with ...+0.1 but it does not work. I am using two arguments of newcommand to define the start and end point of the iteration list, so I do this:
\foreach \x in {#1+0.1,...+0.1,#2+0.1}
– Carlos H. Mendoza-Cardenas Mar 15 '17 at 21:31
What does ...+1 mean? – StrawberryFieldsForever Dec 20 '19 at 11:11

score 4 · Answer 2 · answered Nov 30 '11 at 20:36

With eTeX, you can use \numexpr:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
  \def\I{2}
  \foreach \i in {\number\numexpr\I + 1\relax, ..., 20 }
  \node[anchor=center] at (\i,10) {$+$};
\end{tikzpicture}
\end{document}

score 3 · Answer 3 · answered Nov 30 '11 at 20:19

3

Yo can use \pgfmathsetmacro{\Start}{\I+1} to compute the start point and then use \Start in the \foreach:

\documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
\def\I{2}
\pgfmathsetmacro{\Start}{\I+1}
\foreach \i in { \Start, ..., 20 }
  \node[anchor=center] at (\i,10) {$+$};
\end{tikzpicture}
\end{document}

answered Nov 30 '11 at 20:19

Peter Grill

223,288

Yup, I know that, and that is how I am doing it currently. But I have many such loops and the resulting construct is remarkably inelegant! :D – Mariano Suárez-Álvarez Nov 30 '11 at 20:22

Computing in the list of a tikz foreach

3 Answers3

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