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如何将方程指向曲线

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如何将方程指向曲线

我有以下代码：

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.7}

\begin{document}
\begin{tikzpicture}[>=latex]
\begin{axis}[grid=both,
            axis x line=center,
            axis y line=center,
            black,              
            xlabel={\textit{potential}},
            ylabel={\textit{cost}},
            xlabel style={below right},
            ylabel style={above center},
            xmax=5,
            ymax=2,
            axis lines=middle,
            enlargelimits
            ]

\addplot [mark=none, red, thick] {exp(-x)}
         node [pos=1, pin=500:{%
              \color{black}%
              $\exp(\frac{z_i-z_j}{2\sigma})$%
              }] {};
\end{axis}
\end{tikzpicture}
\end{document}

我需要将公式$\exp(\frac{z_i-z_j}{2\sigma})$指向指数曲线的中间。谢谢！

答案1

这只是一种可能性。

\documentclass[tikz,border=3mm]{standalone}
%\documentclass{article}
\usepackage{pgfplots}
%\pgfplotsset{compat=1.7}

\begin{document}
\begin{tikzpicture}[>=latex]
\begin{axis}[grid=both,  %grid=none
            axis x line=center,
            axis y line=center,
            black,              
            xlabel={$potential$},
            ylabel={$cost$},
            xlabel style={below right},
            ylabel style={above center},
            xmax=5,
            ymax=2,
            axis lines=middle,
            %restrict y to domain=-7:12,
            enlargelimits,
            domain=-.5:5
            ]
\addplot[mark=none, red, thick] {exp(-x)} coordinate[pos=0.3] (aux);
\node[anchor=south west, text=black] (a) at (axis cs:2,0.5) {$\exp(\frac{z_i-z_j}{2\sigma})$};
\draw (aux)--(a.west);
\end{axis}
\end{tikzpicture}
\end{document}

在此处输入图片描述

答案2

在这种情况下，您可以最轻松地控制节点的位置，通过使用图本身的坐标系来定义坐标/节点，并以正常的 TiKZ 样式绘制它们。

来源

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.7}

\begin{document}
\begin{tikzpicture}[>=latex]
\begin{axis}[grid=both,
            axis x line=center,
            axis y line=center,
            black,              
            xlabel={\textit{potential}},
            ylabel={\textit{cost}},
            xlabel style={below right},
            ylabel style={above center},
            xmax=5,
            ymax=2,
            axis lines=middle,
            enlargelimits
            ]

    \addplot [mark=none, red, thick] {exp(-x)};

    \coordinate (P) at (axis cs:1,{exp(-1)});
    \node (label) at (axis cs:3,{1+exp(-1)}) {$\exp(\frac{z_i-z_j}{2\sigma})$};
    \draw [red!50!black, thick, dashed, ->, shorten >=2pt] (label) -- (P);
\end{axis}
\end{tikzpicture}
\end{document}

结果

带有标签和箭头的绘图

答案3

PSTricks 解决方案：

\documentclass{article}

\usepackage{pst-plot}

% approximation to Euler's number
\def\PSEuler{2.71828182845904523536 }
% point on x-axis
\def\point{1.5 }

\begin{document}

\begin{figure}
 \centering
 \psset{yunit = 2}
  \begin{pspicture}(-0.73,-0.27)(7.04,2.5)% found manually
    \psaxes[Dy = 0.5]{->}(0,0)(-0.5,-0.25)(5.5,2.3)[Potential,0][Cost,90]
    \psplot[linecolor = red]{-0.6}{5}{\PSEuler x neg exp}
    \psline{->}%
      (!\point 1 add \PSEuler \point neg 1 add exp)%
      (!\point \PSEuler \point neg exp)
    \uput[90](!\point 1 add \PSEuler \point neg 1 add exp)%
      {$\displaystyle \exp{\mkern -8mu}\left(\frac{z_{i} - z_{j}}{2\sigma}
       \right)$}
  \end{pspicture}
\end{figure}

\end{document}

输出

答案4

MetaPost 解决方案，它对感兴趣的人有用。路径的中间很容易找到元乐趣MetaPost 的格式：point .5 along curve如果是路径的名称。对于 MetaPost 专家，以下是Metafun 格式中二元运算符curve的定义：along

primarydef pct along pat = % also negative
    (arctime (pct * (arclength pat)) of pat) of pat
enddef ;

Metafun 还定义了一个方便的function宏，它生成与函数（或参数曲线）相关的曲线，我在这里使用了它。它还定义了一些宏来生成网格，但我发现它们很难处理，所以我在这里设计了自己的宏，gridlines灵感来自mfpic包裹。

由于我不喜欢标签被网格或曲线交叉，因此我还定义了一个宏来清除每个标签的边界框clearlabel。

使用 LuaLaTeX 进行处理。（需要软件包 2.10.1luamplib或更高版本。）

\documentclass[border=2mm]{standalone}
\usepackage{amsmath, luamplib}
  \mplibsetformat{metafun}
  \mplibtextextlabel{enable}
  \mplibnumbersystem{double}
\begin{document}
  \begin{mplibcode}
    u := 1.25cm; v := 2.5cm;
    Xmin := -.75; Xmax := 5.4; Ymin := -.25; Ymax := 2.25;
    xmin := Xmin; xmax := 5; xstep := .05; ystep := .5;

    def gridlines (expr xmin, xmax, xstep)(expr ymin, ymax, ystep) =
      for i = ceiling(xmin/xstep) upto xmax div xstep:
        draw (i*xstep, ymin) -- (i*xstep, ymax) ;
      endfor 
      for j = ceiling(ymin/ystep) upto ymax div ystep:
        draw (xmin, j*ystep) -- (xmax, j*ystep);
      endfor
    enddef;

    vardef clearlabel@#(expr str, pos) =
      save pic; picture pic; pic = thelabel@#(str, pos);
      unfill boundingbox pic enlarged bp; draw pic
    enddef;

    beginfig(1);
      drawoptions(withcolor .8white);
      gridlines(Xmin*u, Xmax*u, u)(Ymin*v, Ymax*v, .5v);  
      drawoptions();
      drawarrow (Xmin*u, 0) -- (Xmax*u, 0); drawarrow (0, Ymin*v) -- (0, Ymax*v);
      path curve; 
      curve = function(2, "x", "exp -x", xmin, xmax, xstep) xyscaled (u, v);
      draw curve withcolor red;

      picture mylabel; 
      mylabel = thelabel("$\exp\!\Big(\dfrac{z_i-z_j}{2\sigma} \Big)$",
        .5(Xmax*u, Ymax*v));
      drawarrow center bbox mylabel -- point .5 along curve;
      unfill bbox mylabel; draw mylabel;
      for i = 1 upto 5:
        clearlabel.bot("$" & decimal i & "$", (i*u, 0));
      endfor;
      for j = .5 step .5 until 2:
        clearlabel.lft("$" & decimal j & "$", (0, j*v));
      endfor
      label.top("Potential", (Xmax*u, 0)); 
      label.lft("Cost", (0, Ymax*v));
    endfig;
  \end{mplibcode}
\end{document}

在此处输入图片描述

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