大家好，我不知道如何将我想要的箭头添加到此图像中。以下是图像/最小示例以及我的目标。我需要帮助添加箭头：
\documentclass{article}
\usepackage{tikz,geometry}
\begin{document}
\begin{minipage}{.5\textwidth}
\begin{tikzpicture}
\draw[->] (-.5,0)--(6,0) node[below] {$x$};
\draw[->] (0,-.5)--(0,3.5) node[left] {$y$};
\draw [red,<->,thick] plot [smooth,tension=.7,samples=200] coordinates {
(.5,1) (1.25,.5) (2.75,1) (4.5,2.5) (6,1.75) };
\filldraw[black] (1.25,.5) circle (2pt) node[] {$$};
\filldraw[black] (4.5,2.5) circle (2pt) node[] {$$};
\draw (1.25,0) node[below] {\scriptsize $a$} -- (1.25,.5) -- (0,0.5) node
[left] {\scriptsize $f(a)$};
\draw (4.5,0) node[below] {\scriptsize $b$} -- (4.5,2.5) -- (0,2.5) node
[left] {\scriptsize $f(b)$};
\node at (2.75,-1) [align=left] {\scriptsize If the input $a$ is less than
the input $b$,\\ \scriptsize then the output for $a$ is less than the\\
\scriptsize output for $b$.};
\end{tikzpicture}
\end{minipage}
\begin{minipage}{.5\textwidth}
\begin{tikzpicture}
\draw[->] (-.5,0)--(6,0) node[below] {$x$};
\draw[->] (0,-.5)--(0,3.5) node[left] {$y$};
\draw [blue,<->,thick] plot [smooth,tension=.7,samples=200] coordinates {
(.5,2.5) (1.25,2.6) (2.75,1) (4.5,.5) (6,1.25) };
\filldraw[black] (1.25,2.6) circle (2pt) node[] {$$};
\filldraw[black] (4.5,.5) circle (2pt) node[] {$$};
\draw (1.25,0) node[below] {\scriptsize $a$} -- (1.25,2.6) -- (0,2.6) node
[left] {\scriptsize $f(a)$};
\draw (4.5,0) node[below] {\scriptsize $b$} -- (4.5,.5) -- (0,.5) node
[left] {\scriptsize $f(b)$};
\node at (2.75,-1) [align=left] {\scriptsize If the input $a$ is less than
the input $b$,\\ \scriptsize then the output for $a$ is greater than the\\
\scriptsize output for $b$.};
\end{tikzpicture}
\end{minipage}
\end{document}
输出：
我正在尝试添加“增加”和“减少”箭头，如下所示：
答案1
像这样？
\documentclass{article}
\usepackage{geometry}
\usepackage{tikz}
\usetikzlibrary{shapes.arrows}
\begin{document}
\begin{minipage}{.5\textwidth}
\begin{tikzpicture}[font=\scriptsize ]
\draw[->] (-.5,0)--(6,0) node[below] {$x$};
\draw[->] (0,-.5)--(0,3.5) node[left] {$y$};
\draw [red,<->,thick] plot [smooth,tension=.7,samples=200] coordinates {
(.5,1) (1.25,.5) (2.75,1) (4.5,2.5) (6,1.75) };
\filldraw[black] (1.25,.5) circle (2pt) coordinate (start);
\filldraw[black] (4.5,2.5) circle (2pt) coordinate (end);
\path (start) -- (end) node[midway,above,draw=red,single arrow,fill=red!20,sloped]{increasing};
\draw (1.25,0) node[below] {$a$} -- (1.25,.5) -- (0,0.5) node
[left] {$f(a)$};
\draw (4.5,0) node[below] {$b$} -- (4.5,2.5) -- (0,2.5) node
[left] {$f(b)$};
\node at (2.75,-1) [align=left] {If the input $a$ is less than
the input $b$,\\ then the output for $a$ is less than the\\
output for $b$.};
\end{tikzpicture}
\end{minipage}
\begin{minipage}{.5\textwidth}
\begin{tikzpicture}[font=\scriptsize]
\draw[->] (-.5,0)--(6,0) node[below] {$x$};
\draw[->] (0,-.5)--(0,3.5) node[left] {$y$};
\draw [blue,<->,thick] plot [smooth,tension=.7,samples=200] coordinates {
(.5,2.5) (1.25,2.6) (2.75,1) (4.5,.5) (6,1.25) };
\filldraw[black] (1.25,2.6) circle (2pt) coordinate (start);
\filldraw[black] (4.5,.5) circle (2pt) coordinate (end);
\path (start) -- (end) node[midway,above,draw=blue,single
arrow,fill=blue!20,sloped]{decreasing};
\draw (1.25,0) node[below] {$a$} -- (1.25,2.6) -- (0,2.6) node
[left] {$f(a)$};
\draw (4.5,0) node[below] {$b$} -- (4.5,.5) -- (0,.5) node
[left] {$f(b)$};
\node at (2.75,-1) [align=left] {If the input $a$ is less than
the input $b$,\\ then the output for $a$ is greater than the\\
output for $b$.};
\end{tikzpicture}
\end{minipage}
\end{document}
当然，您也可以使用下面的箭头。
\documentclass{article}
\usepackage{geometry}
\usepackage{tikz}
\usetikzlibrary{shapes.arrows}
\begin{document}
\begin{minipage}{.5\textwidth}
\begin{tikzpicture}[font=\scriptsize ]
\draw[->] (-.5,0)--(6,0) node[below] {$x$};
\draw[->] (0,-.5)--(0,3.5) node[left] {$y$};
\draw [red,<->,thick] plot [smooth,tension=.7,samples=200] coordinates {
(.5,1) (1.25,.5) (2.75,1) (4.5,2.5) (6,1.75) };
\filldraw[black] (1.25,.5) circle (2pt) coordinate (start);
\filldraw[black] (4.5,2.5) circle (2pt) coordinate (end);
\path (start) -- (end) node[midway,below=14pt,draw=red,single arrow,fill=red!20,sloped]{increasing};
\draw (1.25,0) node[below] {$a$} -- (1.25,.5) -- (0,0.5) node
[left] {$f(a)$};
\draw (4.5,0) node[below] {$b$} -- (4.5,2.5) -- (0,2.5) node
[left] {$f(b)$};
\node at (2.75,-1) [align=left] {If the input $a$ is less than
the input $b$,\\ then the output for $a$ is less than the\\
output for $b$.};
\end{tikzpicture}
\end{minipage}
\begin{minipage}{.5\textwidth}
\begin{tikzpicture}[font=\scriptsize]
\draw[->] (-.5,0)--(6,0) node[below] {$x$};
\draw[->] (0,-.5)--(0,3.5) node[left] {$y$};
\draw [blue,<->,thick] plot [smooth,tension=.7,samples=200] coordinates {
(.5,2.5) (1.25,2.6) (2.75,1) (4.5,.5) (6,1.25) };
\filldraw[black] (1.25,2.6) circle (2pt) coordinate (start);
\filldraw[black] (4.5,.5) circle (2pt) coordinate (end);
\path (start) -- (end) node[midway,above,draw=blue,single
arrow,fill=blue!20,sloped]{decreasing};
\draw (1.25,0) node[below] {$a$} -- (1.25,2.6) -- (0,2.6) node
[left] {$f(a)$};
\draw (4.5,0) node[below] {$b$} -- (4.5,.5) -- (0,.5) node
[left] {$f(b)$};
\node at (2.75,-1) [align=left] {If the input $a$ is less than
the input $b$,\\ then the output for $a$ is greater than the\\
output for $b$.};
\end{tikzpicture}
\end{minipage}
\end{document}
另一种可能性是使用decorations.markings它，如 pgfmanual 第 587 页所述。
\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{shapes.arrows,decorations.markings}
\begin{document}
\foreach \X in {0.2,0.225,...,0.8}
{\begin{tikzpicture}[font=\scriptsize ]
\draw[->] (-.5,0)--(6,0) node[below] {$x$};
\draw[->] (0,-.5)--(0,3.5) node[left] {$y$};
\draw [red,<->,thick,postaction=decorate,decoration={markings,
mark=at position {\X} with {\path (-1,0.2) --
node[midway,below=14pt,draw=red,single arrow,fill=red!20,sloped,transform shape]{increasing}
(1,0.2);
}}] plot [smooth,tension=.7,samples=200] coordinates {
(.5,1) (1.25,.5) (2.75,1) (4.5,2.5) (6,1.75) };
\filldraw[black] (1.25,.5) circle (2pt) coordinate (start);
\filldraw[black] (4.5,2.5) circle (2pt) coordinate (end);
\draw (1.25,0) node[below] {$a$} -- (1.25,.5) -- (0,0.5) node
[left] {$f(a)$};
\draw (4.5,0) node[below] {$b$} -- (4.5,2.5) -- (0,2.5) node
[left] {$f(b)$};
\node at (2.75,-1) [align=left] {If the input $a$ is less than
the input $b$,\\ then the output for $a$ is less than the\\
output for $b$.};
\begin{scope}[xshift=8cm]
\draw[->] (-.5,0)--(6,0) node[below] {$x$};
\draw[->] (0,-.5)--(0,3.5) node[left] {$y$};
\draw [blue,<->,thick,postaction=decorate,decoration={markings,
mark=at position {\X} with {\path (-1,1) --
node[midway,below,draw=blue,single
arrow,fill=blue!20,sloped,transform shape]{decreasing} (1,1);
}}] plot [smooth,tension=.7,samples=200] coordinates {
(.5,2.5) (1.25,2.6) (2.75,1) (4.5,.5) (6,1.25) };
\filldraw[black] (1.25,2.6) circle (2pt) coordinate (start);
\filldraw[black] (4.5,.5) circle (2pt) coordinate (end);
\draw (1.25,0) node[below] {$a$} -- (1.25,2.6) -- (0,2.6) node
[left] {$f(a)$};
\draw (4.5,0) node[below] {$b$} -- (4.5,.5) -- (0,.5) node
[left] {$f(b)$};
\node at (2.75,-1) [align=left] {If the input $a$ is less than
the input $b$,\\ then the output for $a$ is greater than the\\
output for $b$.};
\end{scope}
\end{tikzpicture}}
\end{document}
至于内联动画：我对此没有太多经验，但我只是用过这个很好的答案并且立即见效。希望所有答案都如此清晰！（使用 acroread 查看。）
\documentclass{article}
\usepackage{animate}
\usepackage{tikz}
\usetikzlibrary{shapes.arrows,decorations.markings}
\begin{document}
\begin{animateinline}[controls,autoplay,loop]{2}
\multiframe{16}{n=1+1}{\begin{tikzpicture}[font=\scriptsize]
\pgfmathsetmacro{\X}{0.175+0.025*\n}
\draw[->] (-.5,0)--(6,0) node[below] {$x$};
\draw[->] (0,-.5)--(0,3.5) node[left] {$y$};
\draw [red,<->,thick,postaction=decorate,decoration={markings,
mark=at position {\X} with {\path (-1,0.2) --
node[midway,below=14pt,draw=red,single arrow,fill=red!20,sloped,transform shape]{increasing}
(1,0.2);
}}] plot [smooth,tension=.7,samples=200] coordinates {
(.5,1) (1.25,.5) (2.75,1) (4.5,2.5) (6,1.75) };
\filldraw[black] (1.25,.5) circle (2pt) coordinate (start);
\filldraw[black] (4.5,2.5) circle (2pt) coordinate (end);
\draw (1.25,0) node[below] {$a$} -- (1.25,.5) -- (0,0.5) node
[left] {$f(a)$};
\draw (4.5,0) node[below] {$b$} -- (4.5,2.5) -- (0,2.5) node
[left] {$f(b)$};
\node at (2.75,-1) [align=left] {If the input $a$ is less than
the input $b$,\\ then the output for $a$ is less than the\\
output for $b$.};
\begin{scope}[xshift=8cm]
\draw[->] (-.5,0)--(6,0) node[below] {$x$};
\draw[->] (0,-.5)--(0,3.5) node[left] {$y$};
\draw [blue,<->,thick,postaction=decorate,decoration={markings,
mark=at position {\X} with {\path (-1,1) --
node[midway,below,draw=blue,single
arrow,fill=blue!20,sloped,transform shape]{decreasing} (1,1);
}}] plot [smooth,tension=.7,samples=200] coordinates {
(.5,2.5) (1.25,2.6) (2.75,1) (4.5,.5) (6,1.25) };
\filldraw[black] (1.25,2.6) circle (2pt) coordinate (start);
\filldraw[black] (4.5,.5) circle (2pt) coordinate (end);
\draw (1.25,0) node[below] {$a$} -- (1.25,2.6) -- (0,2.6) node
[left] {$f(a)$};
\draw (4.5,0) node[below] {$b$} -- (4.5,.5) -- (0,.5) node
[left] {$f(b)$};
\node at (2.75,-1) [align=left] {If the input $a$ is less than
the input $b$,\\ then the output for $a$ is greater than the\\
output for $b$.};
\end{scope}
\end{tikzpicture}}
\end{animateinline}
\end{document}