[Tex/LaTex] If-Then-Else clause in TIkZ Latex

tikz-pgf

I'm continuing my work on the "changeable" graphics. I have an array of values, and I have already succeeded in making variables from it. The next step is that I want to ignore the zero values. Here it is, what I have a problem with:

\pgfmathifthenelse{\myq==0}{}{\fill (B) circle (4pt)};

I thought this code should draw a circle in the node B in case the variable \myq has non-zero value. But I cannot even compile the code, compilation freezes. Can you figure out the possible problem or give an advice?

The whole code is:

\begin{tikzpicture}
\def\zamkl{{3,4,4.5,5}}
\def\zamkh{{4,3.5,5,4.5}}
\def\zamkq{{20,0,30,0}}

\pgfmathparse{\zamkl[0]}
\edef\myl{\pgfmathresult}

\pgfmathparse{\zamkh[0]}
\edef\myh{\pgfmathresult}

\pgfmathparse{\zamkq[0]}
\edef\myq{\pgfmathresult}

\draw[help lines] (0,0) grid (2*\myl,2*\myh);

\coordinate (A) at (0,0);
\coordinate (B) at (\myl,0); \node at (B) [below] {$T$};
\coordinate (C) at (2*\myl,0);
\coordinate (D) at (2*\myl,\myh); \node at (D) [left] {$S$};
\coordinate (E) at (2*\myl,2*\myh);
\coordinate (F) at (\myl,2*\myh); \node at (F) [below] {$R$};
\coordinate (G) at (0,2*\myh);
\coordinate (H) at (0,\myh); \node at (H) [right] {$W$};

\draw [very thick] (A) -- (C) -- (E) --(G) -- (A);

\pgfmathifthenelse{\myq==0}{}{\fill (B) circle (4pt)};

\end{tikzpicture}

Best Answer

With pgfmath the correct syntax is

\pgfmathifthenelse{\myq==0}{}{"\noexpand\fill (B) circle (4pt);"}\pgfmathresult

\pgfmathparse{\myq==0?:"\noexpand\fill (B) circle (4pt);"}\pgfmathresult

Every expression is expanded with \edef before it is parsed. Using \noexpand protects \fill from this expansion. And as always \pgfmathifthenelse returns the result in the macro \pgfmathresult.

Related Solutions

[Tex/LaTex] Convert from physical dimensions to axis cs coordinate values

Originally posted on PGFPlots: How to draw a label at a zero of a function? There may be a better way than this, but I haven't found one yet.

tick marks

\documentclass[border=2pt]{standalone}
\usepackage{pgfplots}
\usetikzlibrary{intersections}

\newlength{\len}
\newlength{\plotwidth}
\newcommand{\getvalue}[1]{\pgfkeysvalueof{/pgfplots/#1}}

%output will be given by \pgfmathresult
\newcommand{\xcoord}[1]% #1 = node name
{\pgfplotsextra{%
  \pgfextractx{\len}{\pgfpointdiff{\pgfplotspointaxisxy{0}{0}}{\pgfpointanchor{#1}{center}}}%
  \pgfextractx{\plotwidth}{\pgfpointdiff{\pgfplotspointaxisxy{\getvalue{xmin}}{0}}%
    {\pgfplotspointaxisxy{\getvalue{xmax}}{0}}}%
  \pgfmathparse{\len*(\getvalue{xmax}-\getvalue{xmin})/\plotwidth}%
}}

\begin{document}

\begin{tikzpicture}
    \begin{axis}[
            axis x line=middle,
            axis y line=middle,
            domain=-4:7
        ]
        \addplot[no marks,blue,thick, name path global=My Graph] {x*x-4*x-7};
        \addplot[no marks,draw=none, name path global=x Axis] {0};
        \path[name intersections={of=My Graph and x Axis,total=\t}];

        \draw[very thin,color=gray] (intersection-1) -- +(0,-5mm) coordinate(tick1);
        \xcoord{tick1}%
        \node[below] at (tick1) {$\pgfmathresult$};

        \draw[very thin,color=gray] (intersection-2) -- +(0,-5mm) coordinate(tick2);
        \xcoord{tick2}%
        \node[below] at (tick2) {$\pgfmathresult$};
     \end{axis}

\end{tikzpicture}
\end{document}

It should be noted than you get the wrong answer if \xcoord is inside a node (text field) or a path, and obviously if any other \pgfmath calculation occurs between it an \pgfmathresult. Also, \pgfplotsconvertunittocoordinate and \pgfplotsunitxlength were tried unsucessfully.

[Tex/LaTex] TikZ: Drawing an arc from an intersection to an intersection

A solution which allows to draw intersection segments of any two intersections is available as tikz library fillbetween.

This library works as general purpose tikz library, but it is shipped with pgfplots and you need to load pgfplots in order to make it work:

\documentclass{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{fillbetween}

\begin{document}

\begin{tikzpicture}

\draw [name path=red,red] (120:1.06) circle (1.9);
%\draw [name path=yellow,yellow] (0:1.06) circle (2.12);
\draw [name path=green,green!50!black] (0:0.77) circle (2.41);
\draw [name path=blue,blue] (0:0) circle (1.06);

% substitute this temp path by `\path` to make it invisible:
\draw[name path=temp1, intersection segments={of=red and blue,sequence=L1}];
\draw[red,-stealth,ultra thick, intersection segments={of=temp1 and green,sequence=L3}];

\end{tikzpicture}

\end{document}

enter image description here

The key intersection segments is described in all detail in the pgfplots reference manual section "5.6.6 Intersection Segment Recombination"; the key idea in this case is to

create a temporary path temp1 which is the first intersection segment of red and blue, more precisely, it is the first intersection segment in the Left argument in red and blue : red. This path is drawn as thin black path. Substitute its \draw statement by \path to make it invisible.
Compute the desired intersection segment by intersecting temp1 and green and use the correct intersection segment. By trial and error I figured that it is the third segment of path temp1 which is written as L3 (L = left argument in temp1 and green and 3 means third segment of that path).

The argument involves some trial and error because fillbetween is unaware of the fact that end and startpoint are connected -- and we as end users do not see start and end point.

Note that you can connect these path segments with other paths. If such an intersection segment should be the continuation of another path, use -- as before the first argument in sequence. This allows to fill paths segments:

\documentclass{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{fillbetween}

\begin{document}

\begin{tikzpicture}

\draw [name path=red,red] (120:1.06) circle (1.9);
%\draw [name path=yellow,yellow] (0:1.06) circle (2.12);
\draw [name path=green,green!50!black] (0:0.77) circle (2.41);
\draw [name path=blue,blue] (0:0) circle (1.06);

% substitute this temp path by `\path` to make it invisible:
\draw[name path=temp1, intersection segments={of=red and blue,sequence=L1}];
\draw[red,fill=blue,-stealth,ultra thick, intersection segments={of=temp1 and green,sequence=L3}]  
    [intersection segments={of=temp1 and green, sequence={--R2}}]
;

\end{tikzpicture}

\end{document}

enter image description here

Best Answer

Related Solutions

[Tex/LaTex] Convert from physical dimensions to axis cs coordinate values

[Tex/LaTex] TikZ: Drawing an arc from an intersection to an intersection

Related Question