使用 \foreach 更改 Pgfplots 中的颜色

Question

我想使用 foreach 和 PGFplots 绘制多条曲线，但每条曲线都有不同的颜色。下面是我给出的代码：

\def\R{1}
\begin{tikzpicture}
\begin{axis}[
    xmin = -1.5, xmax = 1.5,
    %axis x line*=middle,
    ymin = -1.5, ymax = 1.5,
    xtick distance = 1,
    ytick distance = 1,
    xlabel=$x$,
    ylabel=$y$,
    grid = both,
    minor tick num = 2,
    major grid style = {lightgray},
    minor grid style = {lightgray!25},
    width = 0.62\textwidth,
    height = 0.62\textwidth]
    \addplot[
        domain = 0:2*pi,
        samples = 200,
        smooth,
        thick,
    ] ({\R*sin(deg(x))},{\R*cos(deg(x))});
\foreach \r/\w in {0.1/10,0.2/20}{
\addplot[
        domain = 0:2*pi,
        samples = 200,
        smooth,
        thick,
        color=red!\w!blue,
    ] ({(\R-\r)*cos(deg(x))+\r*cos(deg((\R-\r)*x/\r))},{(\R-\r)*sin(deg(x))-\r*sin(deg((\R-\r)*x/\r))});
}
\end{axis}
\end{tikzpicture}

但是，当我在颜色中使用 \w 时，无法编译。有人能帮帮我吗？

Answer 1

这是因为在axis环境中使用循环时存在一个常见的“问题”。而且由于它是一个常见的问题，也有一个解决方案......（这是答案的一个变体https://tex.stackexchange.com/a/305183/95441。）

% used PGFPlots v1.17
\documentclass[border=5pt]{standalone}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
        \def\R{1}
    \begin{axis}[
        xmin=-1.5, xmax=1.5,
        ymin=-1.5, ymax=1.5,
        xtick distance=1,
        ytick distance=1,
        xlabel=$x$,
        ylabel=$y$,
        grid=both,
        minor tick num=2,
        major grid style={lightgray},
        minor grid style={lightgray!25},
        width=0.62\textwidth,
        height=0.62\textwidth,
        domain=0:2*pi,
        samples=201,
        smooth,
    ]
        \addplot[
            thick,
        ] ({\R*sin(deg(x))},{\R*cos(deg(x))});

        \foreach \r/\w in {0.1/25,0.2/75}{
            \edef\temp{\noexpand%
            \addplot[
                thick,
                color=red!\w!blue,
            ] (
                {(\R-\r)*cos(deg(x)) + \r*cos(deg((\R-\r)*x/\r))},
                {(\R-\r)*sin(deg(x)) - \r*sin(deg((\R-\r)*x/\r))}
            );
            }\temp
        }
    \end{axis}
\end{tikzpicture}
\end{document}

Answer 2

使用\pgfplotsinvokeforeach。

\documentclass[border=3mm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.17} 


\begin{document}
\def\R{1}
\begin{tikzpicture}
\begin{axis}[
    xmin = -1.5, xmax = 1.5,
    %axis x line*=middle,
    ymin = -1.5, ymax = 1.5,
    xtick distance = 1,
    ytick distance = 1,
    xlabel=$x$,
    ylabel=$y$,
    grid = both,
    minor tick num = 2,
    major grid style = {lightgray},
    minor grid style = {lightgray!25},
    width = 0.62\textwidth,
    height = 0.62\textwidth]
    \addplot[
        domain = 0:2*pi,
        samples = 200,
        smooth,
        thick,
    ] ({\R*sin(deg(x))},{\R*cos(deg(x))});
\pgfplotsinvokeforeach{10,20}{
\addplot[
        domain = 0:2*pi,
        samples = 200,
        smooth,
        thick,
        color=red!#1!blue,
    ] ({(\R-#1*0.01)*cos(deg(x))+#1*0.01*cos(deg((\R-#1*0.01)*x/(#1*0.01)))},
    {(\R-#1*0.01)*sin(deg(x))-#1*0.01*sin(deg((\R-#1*0.01)*x/(#1*0.01)))});
}
\end{axis}
\end{tikzpicture}
\end{document}