Graphics, Figures & Tables ⇒ sinus plot not perfect

[paulosousa]

Hello all,
I need your help since the sinus plot is not a perfect curve. Why?

Code: Select all

\documentclass[10.5pt, twoside, a4paper]{article}
\usepackage[portuguese]{babel} 
\usepackage[utf8]{inputenc}
\usepackage[left=2.0cm,top=1.5cm,right=2.0cm,bottom=1.75cm]{geometry}
\usepackage{amsmath,amssymb,amsfonts,textcomp,graphicx}
\usepackage{tikz}

\begin{document}

\begin{center}

            \begin{tikzpicture}[scale=0.5]
            \coordinate (O) at (0, 0);
           
            \draw[ultra thick, color=blue][domain=-2.2*pi:2.2*pi]   plot (\x,{sin(\x r)})   node[above right] {$f(x) = \sin x$};
           
            \draw[fill=black] (0,-1) circle (0pt) node[ left ]{{\scriptsize $-1$}};        
            \draw[fill=black] (0,1) circle (0pt) node[ left  ]{{\scriptsize $1$}};        
             \draw[fill=black] (-3.1415,0) circle (0pt) node[below left ]{{\scriptsize $-\pi$}};      
             \draw[fill=black] (3.1415,0) circle (0pt) node[below left ]{{\scriptsize $\pi$}};      
            \draw[fill=black] (6.28,0) circle (0pt) node[below right  ]{{\scriptsize $2\pi$}};        
            \draw[fill=black] (-6.28,0) circle (0pt) node[below   ]{{\scriptsize $-2\pi$}};      
                                
            \draw[ultra thick, ->, >=stealth] (-7, 0) -- (8, 0) node[below]{$x$};
            \draw[ultra thick, ->, >=stealth] (0,-2.5) -- (0, 2.5) node[left]{$y$};
            
            \end{tikzpicture}
        \end{center}

\end{document}

Paulo

[Johannes_B]

Two points form a line. TiKZ doesn't know what it draws or how it looks and sometimes you need to assist by telling how many samples (points) should be used. Or in this case, a simple smooth helps.

Code: Select all

\documentclass[10.5pt,%not valid for article class
twoside, a4paper]{article}
\usepackage[portuguese]{babel}
\usepackage[utf8]{inputenc}
\usepackage[left=2.0cm,top=1.5cm,right=2.0cm,bottom=1.75cm]{geometry}
\usepackage{amsmath,amssymb,amsfonts,textcomp,graphicx}
\usepackage{tikz}

\begin{document}

\begin{center}

	\begin{tikzpicture}[scale=0.9]
		\coordinate (O) at (0, 0);

		\draw[ultra thick, color=blue][domain=-2.2*pi:2.2*pi,samples=20]   plot (\x,{sin(\x r)})   node[above right] {$f(x) = \sin x$};
%		\draw[ultra thick, color=blue][domain=-2.2*pi:2.2*pi,smooth]   plot (\x,{sin(\x r)})   node[above right] {$f(x) = \sin x$};
		\draw[ultra thick, color=red][domain=-2.2*pi:2.2*pi,samples=15]   plot (\x/2,{2*sin(\x r)})   node[above right] {};
%		\draw[ultra thick, color=red][domain=-2.2*pi:2.2*pi,smooth]   plot (\x/2,{2*sin(\x r)})   node[above right] {};
		\draw[ultra thick, color=green][domain=-2.2*pi:2.2*pi,samples=50]   plot (\x,{.5*sin(\x r)})   node[above right] {};
		\draw[ultra thick, color=gray][domain=-2.2*pi:2.2*pi,samples=100]   plot (\x/2,{3*sin(\x r)})   node[above right] {};

		\draw[fill=black] (0,-1) circle (0pt) node[ left ]{{\scriptsize $-1$}};        
		\draw[fill=black] (0,1) circle (0pt) node[ left  ]{{\scriptsize $1$}};        
		\draw[fill=black] (-3.1415,0) circle (0pt) node[below left ]{{\scriptsize $-\pi$}};      
		\draw[fill=black] (3.1415,0) circle (0pt) node[below left ]{{\scriptsize $\pi$}};      
		\draw[fill=black] (6.28,0) circle (0pt) node[below right  ]{{\scriptsize $2\pi$}};        
		\draw[fill=black] (-6.28,0) circle (0pt) node[below   ]{{\scriptsize $-2\pi$}};      

		\draw[ultra thick, ->, >=stealth] (-7, 0) -- (8, 0) node[below]{$x$};
		\draw[ultra thick, ->, >=stealth] (0,-2.5) -- (0, 2.5) node[left]{$y$};

	\end{tikzpicture}
\end{center}

\end{document}