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pgfplots' 之間的填滿與錯誤的段分割

tag-icon • tag-icon pgfplots fillbetween
pgfplots' 之間的填滿與錯誤的段分割

我希望最後一段是白色的，但最後一段似乎是與前一段結合在一起的。

在此輸入影像描述

\documentclass{article} 
\usepackage{tikz}
\usepackage{pgfplots}
\usepgfplotslibrary{fillbetween}
\pgfmathdeclarefunction{vdw}{0}{\pgfmathparse{8.314*115/(x-0.0000364)-0.1358/x/x}}

\begin{document}
\begin{tikzpicture}
  \begin{axis}[
    axis y line = left,
    axis x line = bottom,
    xlabel      = $V$,
    ylabel      = $P$,
    samples     = 500,
    domain      = 0.00005:0.0005,
    xmin = 0, xmax = 0.00055,
    ymin = 0, ymax = 5*10^6,
  ] 
  \addplot[name path=vdw, black, thick, mark=none, ] {vdw}; 
  \addplot[name path=line, gray, no markers, line width=1pt] {2.0*10^6}; 
  \addplot fill between[ 
    of = vdw and line, 
    split, % calculate segments
    every segment no 0/.style={white},
    every segment no 1/.style={orange},
    every segment no 2/.style={red},
    every segment no 3/.style={white},
  ];
\end{axis}

\end{tikzpicture}
\end{document}

答案1

在此輸入影像描述

引用 PGFPLOTS 手冊（第 5.6.8 節陷阱與局限性，第 390 頁），

第一個限制是可擴展性。如果樣本數量很大，底層演算法的效率相對較低，且擴展性很差。請將其應用於合理的樣本量「和具有合理交叉點數量的圖」。這意味著：如果花費的時間太長，您可能需要降低採樣密度。

因此，如果您稍微減少樣本數量（想像一下您的步驟有 500 個樣本；9x10^{-7}太密集），它將給出正確的結果。在這裡，我samples = 200只是透過反覆試驗的方法來選擇。

\documentclass{article} 
\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=1.3}
\usepgfplotslibrary{fillbetween}
\pgfmathdeclarefunction{vdw}{0}{\pgfmathparse{8.314*115/(x-0.0000364)-0.1358/x/x}}

\begin{document}
\begin{tikzpicture}
  \begin{axis}[
    axis y line = left,
    axis x line = bottom,
    xlabel      = $V$,
    ylabel      = $P$,
    samples     = 200,
    domain      = 0.00005:0.0005,
    xmin = 0, xmax = 0.00055,
    ymin = 0, ymax = 5*10^6,
  ] 
  \addplot[name path=vdw, black, thick, mark=none, ] {vdw}; 
  \addplot[name path=line, gray, no markers, line width=1pt] {2.0*10^6}; 
  \addplot fill between[ 
    of = vdw and line, 
    split, % calculate segments
    every segment no 0/.style={white},
    every segment no 1/.style={orange},
    every segment no 2/.style={red},
    every segment no 3/.style={white},
  ];
\end{axis}

\end{tikzpicture}
\end{document}

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