Calculations in TikZ for iterative procedure

Question

In many \foreach iterative procedures in TikZ I would like to relate the generic node called n\x -- where x is a natural number -- to another node the name of which is obtained by applying basic mathemathical relationships to the number used in the name of the former.

Just to be clear, I wolud like to let's say draw a line from n\x to n\x+1 or to n\x*2 or to n\x-3, etc. So if x=4 I would like to draw lines like:

(n4)--(n5)
(n4)--(n8)
(n4)--(n1)

Is this possible?

In the following MWE I would like to draw lines between the nodes using an iterative procedure as previously mentioned.

\documentclass{article}
\usepackage{tikz}
%\usetikzlibrary{calc} <-- Would it be necessary?

\begin{document}

\begin{tikzpicture}
  \matrix[column sep=1cm]{
  \node (n1) {1}; & \node (n2) {2}; & \node (n3) {3}; & \node (n4) {4};\\
  };
  %\foreach \x in {1,...,3} <-- Something like this
  %\draw (n\x)--(n\x+1); 
\end{tikzpicture}

\end{document}

EDIT: This might be related, especially the comment at the end by @Mark Wibrow, but I can't get it to work.

Peter Grill · Accepted Answer · 2014-12-06T18:29:10.517

13

Yes it is possible, you just need to compute \x+1 first. One way to do that is to use \pgfmathtruncatemacro:

enter image description here

Notes:

I added arrows to make it clear that there were three iterations.
As Paul Gaborit pointed out using \pgfmathsetmacro instead of \pgfmathtruncatemacro produces a real number so you get you get 3.0 instead of 3. So the arrow goes to n3.0 (anchor with angle 0 of node n3).

You can also use the evaluate={\TempVar=int(\x+1) syntax:

Code: `\pgfmathtruncatemacro`

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
  \matrix[column sep=1cm]{
  \node (n1) {1}; & \node (n2) {2}; & \node (n3) {3}; & \node (n4) {4};\\
  };
  \foreach \x in {1,...,3} {%<-- Something like this
      \pgfmathtruncatemacro{\TempVar}{\x+1}
      \draw [red, -latex] (n\x)--(n\TempVar); 
  }%
\end{tikzpicture}

Code: `evaluate`

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
  \matrix[column sep=1cm]{
  \node (n1) {1}; & \node (n2) {2}; & \node (n3) {3}; & \node (n4) {4};\\
  };
  \foreach [evaluate={\TempVar=int(\x+1);}] \x in {1,...,3} {%<-- Something like this
      \draw [red, -latex] (n\x)--(n\TempVar); 
  }%
\end{tikzpicture}

edited Dec 06 '14 at 18:29

answered Feb 13 '14 at 18:55

Peter Grill

223,288

1

+1 could you avoid \TempVar by using \pgfmathresult? Is there also an evaluate option of some kind? – cmhughes Feb 13 '14 at 19:01
ah, I see that @TorbjørnT. got the evaluate thing :) – cmhughes Feb 13 '14 at 19:01
@TorbjørnT.: Yep, was just in the process of adding that solution. But, not sure why the results are not the same. – Peter Grill Feb 13 '14 at 19:02
@PeterGrill pgfmathtruncatemacro :) – percusse Feb 13 '14 at 19:46
@PeterGrill: thanks, just what I was looking for (while you were posting your answer I was adding a link in my post to another answer of yours :)). I have a question: where can I find documentation about the use and math operations of evaluate? – Pier Paolo Feb 13 '14 at 20:19
@percusse: Thanks. Was in a hurry as I had to leave so was stumped as to why there was a difference. Would like to think if I was not in such a hurry that I would have figured that out. :-) – Peter Grill Feb 13 '14 at 20:55
1

@PierPaolo: It should be in the TikZ/pgf documentation: TikZ manual newest version online?. – Peter Grill Feb 13 '14 at 20:56
1

@PeterGrill Section 56 of the TikZ/PGF deals with the syntax of \foreach and the evaluate option is discussed there, if I remember correctly :) I'm too lazy to check, tonight. – jub0bs Feb 13 '14 at 21:22
@PeterGrill With \pgfmathsetmacro (without int(...)), you get 3.0 instead of 3. So the arrow goes to n3.0 (anchor with angle 0 of node n3). – Paul Gaborit Dec 06 '14 at 15:20
@PaulGaborit: Ah yes, that explains it. Thanks for clarifying. – Peter Grill Dec 06 '14 at 18:28
@PeterGrill Hello, do you know where the documentation is for this particular form of evaluate = {...} that you used without loading the math library (where it seems to me it's defined)? – AndréC Aug 03 '20 at 08:14
@AndréC: I don't know exactly but should be in the tikz/pgf document. This example loads tikz which loads all the math libraries it needs. – Peter Grill Aug 04 '20 at 08:19
@PeterGrill TikZ does not load the math library by default, you have to ask it, here is the problem because evaluate={...} syntax is only documented in this library. That's why I'm asking myself this question. – AndréC Aug 04 '20 at 08:27
@AndréC: Hmm, that might make a good question. – Peter Grill Aug 04 '20 at 15:40
@PeterGrill That's it : TikZ: Where is documented the syntax evaluate={…} used in foreach loops? – AndréC Aug 04 '20 at 16:28

score 4 · Answer 2 · answered Feb 15 '14 at 22:38

I think you just need expandable computations. Many things can be done with \numexpr.

\documentclass{article}
\usepackage{tikz}
\begin{document}\thispagestyle{empty}
\begin{tikzpicture}
  \matrix[column sep=1cm]{%
    \node (n11) {1}; & \node (n12) {2}; & \node (n13) {3}; & \node (n14) {4};\\
    \node (n21) {1}; & \node (n22) {2}; & \node (n23) {3}; & \node (n24) {4};\\
    \node (n31) {1}; & \node (n32) {2}; & \node (n33) {3}; & \node (n34) {4};\\
    };
  \foreach \x in {1,...,3} {%<-- Something like this
      \draw [red, -latex]
      (n\x\x)--(n\x\the\numexpr\x+1\relax);  
  }%
\end{tikzpicture}
\end{document}

nodes

score 2 · Answer 3 · answered Feb 14 '14 at 00:00

Another version of evaluate:

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
  \matrix[column sep=1cm]{
  \node (n1) {1}; & \node (n2) {2}; & \node (n3) {3}; & \node (n4) {4};\\
  };
  \foreach \x [remember=\x as \lastx (initially 1)] in {2,...,4}{
    \draw [red, -latex] (n\lastx)--(n\x);
  }%
\end{tikzpicture}
\end{document}

enter image description here

score 2 · Answer 4 · answered Feb 16 '14 at 17:48

It's possible to avoid the matrix

 \documentclass{article}
 \usepackage{tikz}

 \begin{document}
 \begin{tikzpicture}
  \node (n1) {1};
   \foreach \x in {2,...,4} {%
     \node (n\x) at (\x-1,0) {\x};
     \draw[red, -latex] (n\the\numexpr\x-1) -- (n\x);    
   }
 \end{tikzpicture}
 \end{document}

enter image description here

Kpym · Answer 5 · 2014-12-07T07:13:20.247

1

As nobody mentioned the use of let, I add this answer for the seek for completeness.

\begin{tikzpicture}
  \matrix[column sep=1cm]{
  \node (n1) {1}; & \node (n2) {2}; & \node (n3) {3}; & \node (n4) {4};\\
  };
  \foreach \a in {1,...,3} {%<-- Something like this (but don't use \x inside let!)
      \draw[red, -latex] let \n{a}={int(\a+1)} in (n\a)--(n\n{a});
  }%
\end{tikzpicture}

enter image description here

edited Dec 07 '14 at 07:13

answered Dec 06 '14 at 11:20

Kpym

23,002

Calculations in TikZ for iterative procedure

5 Answers5

Notes:

Code: `\pgfmathtruncatemacro`

Code: `evaluate`

Linked

Calculations in TikZ for iterative procedure

5 Answers5

Notes:

Code: \pgfmathtruncatemacro

Code: evaluate

Linked

Code: `\pgfmathtruncatemacro`

Code: `evaluate`