附录

Question 1

（根据评论中的要求。）

我和 Phelype 有同样的想法，\addlegendimage为了解决你实际询问的问题。

下面的代码还做了一些其他简化。\closedcycle我没有使用 5 个图来生成垂直虚线，而是使用了一个图\addplot [ycomb, ..]来生成。这在本例中有效，但在其他情况下可能看起来不太好。

此外，使用\pgfplotsset{after end axis...添加节点不必要地复杂。首先，您根本不需要，只需直接在轴环境中\pgfplotsset添加即可。\node[above] at (axis cs:0.55,0.85){\small{$63\%$}};

但请注意，node可以将 a 附加到 a 的末尾\addplot coordinates {...}，因此

\addplot[black, <-] coordinates {(0.55,0.61) (0.55,0.85)}
      node[above,font=\small] {$63\%$};

反而似乎更方便。还请注意，这\small不是一个接受参数的宏，而是一个影响同一组中后续文本的开关，因此应用作{\small text}，而不是\small{text}。

\documentclass{article}

\usepackage{pgfplots} % also loads tikz
\pgfplotsset{compat=1.13}    

\begin{document}

\begin{tikzpicture} 
    \begin{axis}[domain=0:5,
                     xmin=0, xmax=5,
                     ymin=0, ymax=1,
                     axis on top,
                 samples=100,
                 xlabel={time (sec)},
                 ylabel={$dP/dt$},
                 axis line style={line width=1pt}
]

    % not saying this is better or worse, but you can make do with fewer settings
    \addplot [ultra thick, black, fill, fill opacity=0.2] {exp(-x)} \closedcycle;
    \addlegendentry{$R=1Hz$};

    % add custom legend entry
    \addlegendimage{area legend,dashed, thick,fill = black, fill opacity=0.2}
    \addlegendentry{Relative probability}

    % use ycomb to draw the vertical dashed lines
    \addplot[black, dashed, thick, ycomb, samples at={0,...,5}] {exp(-x)};

    \addplot[black, <-] coordinates {(0.55,0.61) (0.55,0.85)}
          node[above,font=\small] {$63\%$};
    \addplot[black, <-] coordinates {(1.55,0.23) (1.55,0.47)}
          node[above,font=\small] {$23\%$};
    \addplot[black, <-] coordinates {(2.55,0.092) (2.55,0.332)}
          node[above,font=\small] {$8.6\%$};
    \addplot[black, <-] coordinates {(3.55,0.040) (3.55,0.28)}
          node[above,font=\small] {$3.1\%$};
    \addplot[black, <-] coordinates {(4.55,0.021) (4.55,0.261)}
          node[above,font=\small] {$1.2\%$};
    \end{axis}
\end{tikzpicture}
\end{document}

附录

如果需要，您可以使用循环使箭头更加自动化。以下代码演示了一种可能的方法，其结果是：

\documentclass{article}

\usepackage{pgfplots} % also loads tikz
\pgfplotsset{compat=1.13}    

\begin{document}

\begin{tikzpicture} 
    \begin{axis}[domain=0:5,
                     xmin=0, xmax=5,
                     ymin=0, ymax=1,
                     axis on top,
                 samples=100,
                 xlabel={time (sec)},
                 ylabel={$dP/dt$},
                 axis line style={line width=1pt}
]

    % not saying this is better or worse, but you can make do with fewer settings
    \addplot [ultra thick, black, fill, fill opacity=0.2] {exp(-x)} \closedcycle;
    \addlegendentry{$R=1Hz$};

    % add custom legend entry
    \addlegendimage{area legend,dashed, thick,fill = black, fill opacity=0.2}
    \addlegendentry{Relative probability}

    % use ycomb to draw the vertical dashed lines
    \addplot[black, dashed, thick, ycomb, samples at={0,...,5}] {exp(-x)};

    \pgfplotsinvokeforeach{0.5,1.5,2.5,3.5,4.5}{ % insert the x-values where you want arrows
       \addplot [<-, shorten <=2pt] coordinates {(#1,{exp(-#1)})(#1,{exp(-#1) + 0.24})}
          node[above,font=\small] {%
            \pgfmathparse{exp(-#1)*100}%
            $\pgfmathprintnumber[precision=1]{\pgfmathresult}\%$};
    }


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

Answer