[Tex/LaTex] TikZ: Parametric Gnuplot plot fails to appear

graphstikz-pgf

I am trying to create a parametric curve using the source code below. It will not show up on my graph at all. The curve is supposed to look like this:

enter image description here

\documentclass{article}
\usepackage{tikz}
\begin{document}
\tikzstyle{textbox}=[draw=white, fill=white, thick, rectangle]
\begin{tikzpicture}[scale=2, domain=-4:4]
   \draw [<->,thick] (-4,0)--coordinate(x axis)(4,0) node[right]{$x$};
   \draw [<->, thick] (0,-4)--coordinate(y axis)(0,4) node[above] {$y$};
   \foreach \x/\xtext in {-3.5/-3.5, -1.5/-1.5, 1.5/1.5, 3.5/3.5}
   \draw[shift={(\x,0)}] (0pt,2pt)--(0pt,-2pt);
   \node [below] at (-3.5,-0.) {$-2\pi$};
   \node [below] at (-1.5,-0.) {$-\pi$};
   \node [below] at (1.5,-0.) {$\pi$};
   \node [below] at (3.5,-0.) {$2\pi$};
   \foreach\y/\ytext in {-3.5/-3.5, -1.5/-1.5, 1.5/1.5, 3.5/3.5}
   \draw [shift={(0,\y)}] (2pt,0pt)--(-2pt,0pt);
   \node [left] at (-0.,3.5) {$2\pi$};
   \node [left] at (-0.,1.5) {$\pi$};
   \node [right] at (0.,-1.5) {$-\pi$};
   \node [right] at (0.,-3.5) {$-2\pi$}; 
   \draw [color=red] plot[id=cos] function{y=t+2cos5t};
   \draw [color=blue] plot[id=sin] function{x=t+2sint};
\end{tikzpicture}
\end{document}

Best Answer

There are few things wrong here. You've not told TikZ that the plot is parametric, you've not put both the x and y components into a single \draw line and you've not given the formulae in the correct form. You can tell something is up as Gnuplot warns

"test.cos.gnuplot", line 2: undefined variable: t
"test.sin.gnuplot", line 2: undefined variable: t

in the log. Changing the input to

\draw [samples=1000] plot[parametric] function{t+2*sin(2*t),t+2*cos(5*t)};

gives me a plot :it's a one-line change so I've not included everything else. To get your plot, i'd also up the domain to say -7:7.

Personally, I'd use pgfplots, which uses the same underlying ideas but is I find easier to read. For example

\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{compat=1.11}
\begin{document}
\begin{tikzpicture}
  \begin{axis}
    [
      axis lines  = center                                ,
      xtick       = {-6.28318,-3.14159,...,6.3}           ,
      xticklabels = {$-2\pi$, $-\pi$, $0$, $\pi$, $2\pi$} ,
      ytick       = {-6.28318,-3.14159,...,6.3}           ,
      yticklabels = {$-2\pi$, $-\pi$, $0$, $\pi$, $2\pi$}
    ]
    \addplot[domain = -7:7, parametric, samples = 1000]
      gnuplot {t+2*sin(2*t),t+2*cos(5*t)};
  \end{axis}
\end{tikzpicture}
\end{document}

which gives

enter image description here

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