如何使用 tikz 绘制一个圆圈：\draw[black, line width = 0.50mm] plot[smooth,domain=0:2] (\x, {sqrt(1-(x-1)^2)});

Question

如何在 tikz 中使用此代码绘制一个圆圈：

\documentclass{article}
\usepackage{tikz,pgfplots}
%\usepackage[x11names]{xcolor}
\usepackage{tikz}


\usetikzlibrary{intersections}

\pgfdeclarelayer{bg}    % declare background

\pgfsetlayers{bg,main}  % order of layers (main = standard layer)

\pgfplotsset{compat=1.13}
\usepackage{amsmath}
\usetikzlibrary{positioning}



\begin{document}






\begin{tikzpicture}
    \draw[black, line width = 0.50mm]   plot[smooth,domain=0:2] (\x, {sqrt(1-(x-1)^2)});
\end{tikzpicture}

\end{document}

Answer 1

呃，那是半个圆圈。你的目的到底是什么？

绘制函数pgfplots比基本tikz

\documentclass{standalone}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
  \begin{axis}[
    axis equal
    ]
    \addplot [smooth,domain=0:2,samples=101] {sqrt(1-(\x-1)^2)};
    \addplot [smooth,domain=0:2,samples=101] {-sqrt(1-(\x-1)^2)};
  \end{axis}
\end{tikzpicture}
\end{document}

Answer 2

您可能希望圆是平滑的，因此可能希望一次性绘制圆。这可以通过使用从 0 到 2 再返回的函数来实现，

(\x<2 ? \x : 4-\x)

然后你需要用 来决定你是在上分支还是下分支sign(2-\x)，这样 plot 命令就变成了

  \draw[black, line width = 0.50mm] 
    plot[smooth cycle,domain=0:4,samples=101] 
  ({(\x<2 ? \x : 4-\x)}, {sign(2-\x)*sqrt(1-((\x<2 ? \x : 4-\x)-1)^2)});

这比标准的圆形路径需要付出的努力要多得多。

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[nodes={text width=2.5cm,align=center}]
 \begin{scope}[local bounding box=A]
  \draw[black, line width = 0.50mm] 
    plot[smooth cycle,domain=0:4,samples=101] 
  ({(\x<2 ? \x : 4-\x)}, {sign(2-\x)*sqrt(1-((\x<2 ? \x : 4-\x)-1)^2)});
 \end{scope}
 \path (A.south) node[below] {engineering a function};
 %
 \begin{scope}[xshift=3cm,local bounding box=B,
    declare function={xcheat(\x)=(\x<2 ? \x : 4-\x);}]
  \draw[black, line width = 0.50mm] 
    plot[smooth cycle,domain=0:4,samples=101] 
  ({xcheat(\x)}, {sign(2-\x)*sqrt(1-(xcheat(\x)-1)^2)});
 \end{scope}
 \path (B.south) node[below] {engineering and declaring a function};
 %
 \begin{scope}[xshift=6cm,local bounding box=C]
  \draw[black, line width = 0.50mm] (1,0) circle[radius=1cm];
 \end{scope}
 \path (C.south) node[below] {use normal circle};
\end{tikzpicture}
\end{document}