[Tex/LaTex] Graphing a sinusoidal function

tikz-pgf

I would like to plot the graph for y = |sin(pi*x)| on the interval -2.5 and 2.5. (The graph is on or above the x-axis, and both ends are at height 1.) TikZ plots a line through the origin. The label for the graph should be to the right end of the graph – it can extend past the x-axis. How to I add the label "x" to the x-axis and "y" to the y-axis?

\documentclass[10pt]{amsart}
\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=1.11}


\begin{document}

\hspace*{\fill}
\begin{tikzpicture}
\begin{axis}[width=4in,axis equal image,
          xmax=3,ymax=1.5,
          axis lines=middle,
          restrict y to domain=-1:2,
          enlargelimits,
          axis line style={shorten >=-0.25cm,shorten <=-0.25cm,latex-latex},
          ticklabel style={fill=white},
          extra x ticks={-2,-1,0,1,2},
          %extra x tick style={grid=none}
]

\addplot[domain=-2.5:2.5,mark=none,samples=200] {abs(sin(pi(x)))} node[fill=white, below left, yshift=-3pt]{$y=\vert\sin(\pi x)\vert$};


\end{axis}
\end{tikzpicture}
\hspace{\fill}

Best Answer

As noted by percusse, adding xlabel and ylabel to axis options solves the label issue.

Another issue is plotting the correct function, which is solved by modifying the formula in \addplot. Note that pgfplots natively operates on degrees, so a conversion from radians to degrees by deg() is needed. Also an explicit multiplication must be done: pi*x instead of pi(x).

Edit: Thanks to Jake for the comment that there is another way to use radians with pgfplots version 1.11 or later. Quoting the change log at http://pgfplots.sourceforge.net/:

new feature: 'trig format plots=rad' allows to use radians in trigonometric evaluations

So, if trig format plots=rad is added to axis options, deg() is no longer needed.

Example using `deg()`

output of example code

\documentclass[10pt]{amsart}
\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=1.11}

\begin{document}

\hspace*{\fill}
\begin{tikzpicture}
\begin{axis}[width=4in,axis equal image,
          xmax=3,ymax=1.5,
          axis lines=middle,
          enlargelimits,
          axis line style={shorten >=-0.25cm,shorten <=-0.25cm,latex-latex},
          ticklabel style={fill=white},
          extra x ticks={0},
          xlabel=$x$,ylabel=$y$,
          clip=false,
]

\addplot[domain=-2.5:2.5,mark=none,samples=200] {abs(sin(deg(pi*x)))} node[fill=white, right]{$y=\vert\sin(\pi x)\vert$};

\end{axis}
\end{tikzpicture}
\end{document}

Related Solutions

[Tex/LaTex] Line up nested tikz enviroments or how to get rid of them

As is explained in How do I draw shapes inside a tikz node? pics can be used for defining new objects. My main problem using pics is how to place where you want because they aren't nodes and positioning them is not so easy.

Following code shows how to define EDFA block.

    EDFA/.pic={
        \begin{scope}[scale=.5]
        \draw (-1,0) coordinate (in) --  (-1,1) -- (1,0) coordinate (out) --  (-1,-1) -- cycle;
        \node[anchor=north,inner sep=2pt] at (0,-1) {$1$};
        \end{scope}

In this case, coordinate (-1,0) will act as west anchor and 1,0 as east. Both point will have an special name for further reference. Every pic is placed according its own origin (0,0). You can use Claudio's answer to Anchoring TiKZ pics for better positioning.

As your example was simple, I'd prefer to star with EDFA and place Source and Sink after it.

\documentclass[]{article}

% tikz
\usepackage{tikz}
\usetikzlibrary{positioning} %relative positioning

\begin{document}

\tikzset{%
    EDFA/.pic={
        \begin{scope}[scale=.5]
        \draw (-1,0) coordinate (in) --  (-1,1) -- (1,0) coordinate (out) --  (-1,-1) -- cycle;
        \node[anchor=north,inner sep=2pt] at (0,-1) {$1$};
        \end{scope}
    }
}

\begin{tikzpicture}[
block/.style={draw},
]

\draw pic (edfa) {EDFA};

\node[block, left=of edfain] (source) {Source};

\node[block, right= of edfaout] (sink) {Sink};

\draw[->] (source) -- (edfain);
\draw[->] (edfaout) -- (sink);

\end{tikzpicture}

\end{document}

I understand that your components are more complex than EDFA because for this particular case an isosceles triangle node with a label will do the work and it can be used as a node and not as a pic:

\documentclass[]{article}

% tikz
\usepackage{tikz}
\usetikzlibrary{positioning} %relative positioning
\usetikzlibrary{shapes.geometric}

\begin{document}

\begin{tikzpicture}[
    block/.style={draw},
    edfa/.style={isosceles triangle, minimum width=1cm, 
         draw, anchor=west, isosceles triangle stretches, 
         minimum height=1cm, label=-80:#1}
]

\node[block] (source) {Source};

\node[edfa=1, right=of source] (edfa) {};

\node[block, right= of edfa] (sink) {Sink};

\draw[->] (source) -- (edfa);
\draw[->] (edfa) -- (sink);

\end{tikzpicture}

\end{document}

[Tex/LaTex] Graphing the Thomae Function

Welcome to TeX.SE! Here is a proposal. Of course, this is just a cartoon because I had to cut off q, as is done in your screen shot.

EDIT: In my previous version there was a huge conceptual flaw. Big big thanks to Peter Grill for bringing it to my attention!

\documentclass[tikz,border=3.14mm]{standalone}
\begin{document}
\begin{tikzpicture}[scale=8]
\draw [-stealth] (-0.1,0) -- (1.1,0);
\draw [-stealth] (0,-0.1) -- (0,0.6);
\foreach \X in {1,...,7}
{\ifnum\X=1
\else
\draw (0.02,1/\X) -- (-0.02,1/\X) node[left,xshift={(-(1+pow(-1,\X)))*3pt}]{$\frac{1}{\X}$};
\fi
}
\foreach \X [evaluate=\X as \Ymax using {int(\X-1)}]in {25,24,...,2}
{\foreach \Y in {1,...,\Ymax}
 {\ifnum\X<6
 \draw (\Y/\X,0.02) -- (\Y/\X,-0.02) node[below,fill=white]{$\frac{\Y}{\X}$};
 \else
 \draw[ultra thin] (\Y/\X,0.01) -- (\Y/\X,-0.01);
 \fi
 \pgfmathtruncatemacro{\TST}{gcd(\X,\Y)}
 \ifnum\TST=1
 \fill ({\Y/\X},1/\X) circle(0.2pt); 
 \fi
 }
}
\foreach \X in {0,1,...,80}
{\fill (\X/80,0) circle(0.2pt); }
\end{tikzpicture}
\end{document}

Best Answer

Example using deg()

Related Solutions

[Tex/LaTex] Line up nested tikz enviroments or how to get rid of them

[Tex/LaTex] Graphing the Thomae Function

Related Question

Example using `deg()`