[Tex/LaTex] TikZ edge thickness causing errors in foreach loop

tikz-pgftikz-styles

I'm experiencing some weirdness in making a simple TikZ diagram (a comb-shaped graph with variable number of nodes). The weirdness comes from the style applied to the edge paths. Here's the (minimal) example:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\begin{document}

\begin{tikzpicture}[auto,scale=1.0,%
block/.style = {draw,circle,very thick,minimum size=0.5cm},%
directed/.style ={draw,-triangle 45, shorten >= 0pt, very thick}]

% Parameters
\pgfmathsetmacro{\numXnodes}{int(3)}
\pgfmathsetmacro{\strch}{2}

\foreach \i in {1,...,\numXnodes}{
    \path (\strch*\i-\strch, 0) node[block] (x\i) {\i};
    \path (x\i) ++(0,-\strch) node[block] (z\i) {\pgfmathparse{int(\numXnodes+\i)}\pgfmathresult};
    \path (x\i) [directed] -- (z\i);
}

\pgfmathsetmacro{\nnmo}{{int(\numXnodes-1)}}

\foreach \i in {1,...,\nnmo} {
    \pgfmathparse{int(\i+1)}
    \draw (x\i) [draw,-triangle 45,thick] -- (x\pgfmathresult);
}

\end{tikzpicture}
\end{document}

The above code draws a graph with the right structure/directionality. However, the edges between "x" nodes are very thin.

The issue is that if I change the style on the line
\draw (x\i) [draw,-triangle 45] -- (x\pgfmathresult);
to \draw (x\i) [draw,-triangle 45,thick] -- (x\pgfmathresult); I get an error that says Package pgf Error: No shape named x0 is known. } (followed by: )

Any thoughts on why this error would be occurring here and not in the first set of edges drawn with the defined directed style (i.e., in the first loop)?

Thanks in advance!

Best Answer

\pgfmathresult macro is overwritten at almost every step of code so you need to be quick to use its value. Most probably, thick option causes a temporary calculation and removes your result. Instead you can use the [count=\variable from number] option.

I would really recommend not using \i as the counter since if it doesn't get expanded properly or else, you will have the greek dotless i character iota in the variable which might go unnoticed until you debug for some time. Moreover, you can also use \pgfmathtruncatemacro to get the integer part automatically.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\begin{document}

\begin{tikzpicture}[auto,scale=1.0,%
block/.style = {draw,circle,very thick,minimum size=0.5cm},%
directed/.style ={draw,-triangle 45, shorten >= 0pt, very thick}]

% Parameters
\pgfmathtruncatemacro{\numXnodes}{3} % \def or \newcommand would also be OK here. 
\pgfmathtruncatemacro{\strch}{2}

\foreach \x in {1,...,\numXnodes}{
    \path (\strch*\x-\strch, 0) node[block] (x\x) {\x};
    \path (x\x) ++(0,-\strch) node[block] (z\x) {\pgfmathparse{int(\numXnodes+\x)}\pgfmathresult};
    \path (x\x) [directed] -- (z\x);
}

\pgfmathtruncatemacro{\nnmo}{\numXnodes-1}

\foreach \x[count=\xi from 2] in {1,...,\nnmo} {
    \draw (x\x) [draw,-triangle 45,thick] -- (x\xi);
}

\end{tikzpicture}
\end{document}

enter image description here

Related Solutions

[Tex/LaTex] TikZ: Using Loop to Draw Grid of Nodes

It's possible to use a minimum code

\documentclass{minimal}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}[darkstyle/.style={circle,draw,fill=gray!40,minimum size=20}]
  \foreach \x in {0,...,4}
    \foreach \y in {0,...,4} 
       {\pgfmathtruncatemacro{\label}{\x - 5 *  \y +21}
       \node [darkstyle]  (\x\y) at (1.5*\x,1.5*\y) {\label};} 

  \foreach \x in {0,...,4}
    \foreach \y [count=\yi] in {0,...,3}  
      \draw (\x\y)--(\x\yi) (\y\x)--(\yi\x) ;

\end{tikzpicture}
\end{document}

enter image description here

Only for information you can get the grid with tkz-berge

\documentclass[border=0.25cm]{standalone}
\usepackage{tkz-berge}

\begin{document}

 \begin{tikzpicture}
      \GraphInit[vstyle=Shade]
   \grGrid[Math,RA=2,RB=2]{5}{5}
 \end{tikzpicture}

\end{document}

enter image description here

[Tex/LaTex] Draw a path between many nodes using foreach

In my opinion, this is a bug in TikZ. As is well-known on this site (!) the PGF \foreach command executes its innards inside a group (actually, two groups). This means that when something is meant to be remembered from one iteration to the next, there has to be an explicit mechanism for remembering it. When the \foreach construction is used to build a path then there are some obvious things that need to be remembered, such as the last point constructed and the last "saved" point. So when TikZ encounters a \foreach in the path construction then it actually calls a wrapper around the PGF \foreach which includes this "saving" apparatus.

However, it would appear that the implementation forgot to remember something. When TikZ encounters a bare node coordinate, such as (p1), then it can't immediately construct the path at this point. The path will lead up to a point on the node's border, but will then hop to some other point on the node's border and that hop will be determined by the next bit of the path. So TikZ remembers that there is a moveto which is "waiting" and figures it out when it knows what the next bit of the path will be.

Unfortunately, this waiting moveto is not part of what is remembered when it goes around the \foreach iteration. So it reverts to the previously remembered moveto which was the one set up before all the grouping started, namely (p1).

A solution is to make TikZ remember that moveto between groups. Here's an adaptation of \tikz@foreach which adds in this rememberence. I have a suspicion that there are a few other things that ought to be remembered between loops as well, such as \tikzlastnode, but to avoid overcomplicating the code I haven't put them in.

\documentclass{article}
%\url{http://tex.stackexchange.com/q/75146/86}
\usepackage{tikz}

\makeatletter
\def\tikz@foreach{%
  \def\pgffor@beginhook{%
    \tikz@lastx=\tikz@foreach@save@lastx%
    \tikz@lasty=\tikz@foreach@save@lasty%
    \tikz@lastxsaved=\tikz@foreach@save@lastxsaved%
    \tikz@lastysaved=\tikz@foreach@save@lastysaved%
    \let\tikz@moveto@waiting=\tikz@foreach@moveto@waiting
    \setbox\tikz@figbox=\box\tikz@tempbox\expandafter\tikz@scan@next@command\pgfutil@firstofone}%
  \def\pgffor@endhook{\pgfextra{%
      \xdef\tikz@foreach@save@lastx{\the\tikz@lastx}%
      \xdef\tikz@foreach@save@lasty{\the\tikz@lasty}%
      \xdef\tikz@foreach@save@lastxsaved{\the\tikz@lastxsaved}%
      \xdef\tikz@foreach@save@lastysaved{\the\tikz@lastysaved}%
      \global\let\tikz@foreach@moveto@waiting=\tikz@moveto@waiting
      \global\setbox\tikz@tempbox=\box\tikz@figbox\pgfutil@gobble}}%
  \def\pgffor@afterhook{%
    \tikz@lastx=\tikz@foreach@save@lastx%
    \tikz@lasty=\tikz@foreach@save@lasty%
    \tikz@lastxsaved=\tikz@foreach@save@lastxsaved%
    \tikz@lastysaved=\tikz@foreach@save@lastysaved%
    \let\tikz@moveto@waiting=\tikz@foreach@moveto@waiting
    \setbox\tikz@figbox=\box\tikz@tempbox\tikz@scan@next@command}%
  \global\setbox\tikz@tempbox=\box\tikz@figbox%
  \xdef\tikz@foreach@save@lastx{\the\tikz@lastx}%
  \xdef\tikz@foreach@save@lasty{\the\tikz@lasty}%
  \xdef\tikz@foreach@save@lastxsaved{\the\tikz@lastxsaved}%
  \xdef\tikz@foreach@save@lastysaved{\the\tikz@lastysaved}%
    \global\let\tikz@foreach@moveto@waiting=\tikz@moveto@waiting
  \foreach}
\makeatother

\begin{document}

\begin{tikzpicture}[scale=.5]
    \foreach [count=\x] \pt in {(0,5), (0,2), (2,2), (2,0), (6,0), (6,2), (8, 2), (8,6), (6,6), (6,8), (3,8)}
        \node[black, circle, draw] (p\x) at \pt {};

    \draw (p1)
        \foreach \x in {2,...,11} {
           -- (p\x)
        };
\end{tikzpicture}
\end{document}

Result:

Foreach with remembered movetos

Best Answer

Related Solutions

[Tex/LaTex] TikZ: Using Loop to Draw Grid of Nodes

[Tex/LaTex] Draw a path between many nodes using foreach

Related Question