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绘制上方和下方渐近线的三次函数

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绘制上方和下方渐近线的三次函数

第一次发帖，长期潜水。我正在尝试在 LaTeX 中重新创建 DNA/蛋白质变性曲线。

我希望曲线看起来是这样的：

DNA 变性/熔化曲线

以下是我的“统计数据”：

  1. 我正在 TeXStudio 中编写并编译为 pdf。
  2. 我正在使用 TikZ 和 pgfplots 包。

这是我的代码：

\documentclass{article}
\usepackage{geometry}
\usepackage{graphicx}
\usepackage{wrapfig}
\usepackage{float}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{arrows,positioning,shapes,decorations,automata,backgrounds,petri}
\usepackage{pgfplots}
\usepgfplotslibrary{polar}
\usepgflibrary{shapes.geometric}
\usepgfplotslibrary{patchplots}
\usetikzlibrary{pgfplots.patchplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{calc}
\usepackage{caption}
\usepackage{subcaption}
\usepackage{mathtools}
\usepackage{chemfig}
\usepackage{setspace}
\usepackage{parskip}
\usepackage{amssymb}
\usepackage{booktabs,array,dcolumn}
\usepackage{etoolbox}
\usepackage[framemethod=TikZ]{mdframed}

\pgfplotsset{my style/.append style={axis x line=middle, axis y line=middle, xlabel={$x$}, ylabel={$y$}, axis equal }}

\begin{document}
\begin{figure}[H]
    \centering
\begin{tikzpicture}
\begin{axis}[xmin=50, xmax=90, ymin=1.0, ymax=1.4, xlabel= Temperature ($^\circ$C), ylabel= Relative Absorbance (260 nm) ]

 \addplot[color=blue, domain=50:90, samples= 100, no marks, x filter/.expression = {y==1.335 ? inf:x}] expression { 
    %(50, 1.01) (69, 1.02)
    %(75, 1.2) (90, 1.335)
    x^(3)+x^(2)+x^(1)}; 

 %\addplot[color=green,mark=x] coordinates{ 
    %(50, 1.033) (54, 1.036) 
    %(56,1.04) (62,1.32) 
    %(63.5,1.35) (74, 1.35) }; these interpolation point coordinates are averaged for the following coordinates:
    
 \addplot[color=red, domain=50:90, samples= 100, no marks, x filter/.expression = {y==1.335 ? inf:x}] expression {
    %(50, 1.033) (55, 1.038)
    %(62.75,1.335) (74, 1.335)
    x^(3)+x^(2)+x^(1)};

 \legend{High AT, High GC} 
 
 \end{axis}
 
 \end{tikzpicture}
\end{figure}
\end{document}

对于所有内容，我深表歉意！这是一份相当大的文档的一部分。

答案1

我不熟悉这个主题，但这张图片看起来像逻辑函数。下面的代码绘制了一个这样的函数，其最小值和最大值如图像中所示。

我删减了序言，只保留必要的部分。

代码输出

\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{compat=1.15} % recommended to use specific version
\begin{document}
\begin{figure}
    \centering
\begin{tikzpicture}[
   declare function={
     k=0.3; % range 
     x0=75; % midpoint
     L=0.3; % steepness
     dna(\x)=1 + L/(1+exp(-k*(\x-x0))); % logistic function (https://en.wikipedia.org/wiki/Logistic_function)
  }
]
\begin{axis}[
  xmin=30,
  xmax=119,
  ymin=0.95,
  ymax=1.35,
  % put y-axis only on the left side of axis
  axis y line=left,
  % remove arrow tip
  axis line style={-},
  xlabel=Temperature ($^\circ$C),
  ylabel=Relative Absorbance (260 nm),
  % move legend
  legend pos=north west
]

 % plot main function
 \addplot[color=blue, domain=40:100, samples=100, no marks] {dna(x)}; 

 % plot upper asymptote
 % "forget plot" means it's not included in the legend
 \addplot[forget plot, blue, dashed,samples at={100,120}] {dna(100)};

 % draw dashed line
 % \pgfkeysvalueof{/pgfplots/ymin} is the ymin of the axis, similarly for xmax
 % x0 is defined with "declare function" above
 \draw [dashed] (x0,\pgfkeysvalueof{/pgfplots/ymin}) |- 
                (\pgfkeysvalueof{/pgfplots/xmax},{dna(x0)});

 \legend{High AT, High GC} 

 \end{axis}

% second axis used to make the ticks and label on the right side
% use same ymin/ymax as previous axis, but custom ticklabels
\begin{axis}[
  axis x line=none,
  axis y line=right,
  axis line style={-},
  ylabel=Degree of denaturation (\%),
  xmin=40,xmax=120,
  ymin=0.95, ymax=1.35,
  ytick={1,1.15,1.3},
  yticklabels={0,50,100}
]

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

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