LaTeX Forum

\documentclass[a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage{mathtools}
\usepackage{tikz}
\usetikzlibrary{arrows}

\begin{document}
  \begin{tikzpicture}[
    declare function={f(\x)=-\x^3+\x;},
    scale=10,
    >=stealth
  ]
    \draw[<->] (0,0.5) node[above left] {$P$} |- (1.25,0) node[below right] {$V$};
    \draw[domain=0:1,samples=50] plot (\x,{f(\x)});
    \foreach \x in {0.3,0.577,0.8}
      \draw[-*,dashed,shorten >=-2pt] (\x,0) -- (\x,{f(\x)});
    \draw (0.3,{f(0.3)}) node[above left] {$\dfrac{dP}{dV}>0$};
    \draw (0.577,{f(0.577)}) node[above] {$\dfrac{dP}{dV}=0$};
    \draw (0.8,{f(0.8)}) node[above right] {$\dfrac{dP}{dV}<0$};
    \draw[->] (0.2,-0.025) -- (0.4,-0.025) node[midway,below] {Increase $V_\text{out}$};
    \draw[<-] (0.7,-0.025) -- (0.9,-0.025) node[midway,below] {Decrease $V_\text{out}$};
    \draw (0.577,{f(0.577)}) node[above=2.5em] {Optimum $V_\text{out}$};
  \end{tikzpicture}
\end{document}

\documentclass[border=1cm]{standalone}
\usepackage{pgfplots}
\usetikzlibrary{arrows}
\begin{document}

\begin{tikzpicture}
\begin{axis}[domain=-2:2]
\addplot+[mark=none, samples=100]{sqrt(2*pi)*exp(-.5*x^2)};
\node at (axis description cs:.5,.95) {$\frac{dP}{dV} = 0$};
\node at (axis description cs:.18,.5) {$\frac{dP}{dV} >0$};
\draw[o-] (axis description cs:.25,.44) -- (axis description cs:.25,0);
\end{axis}

\end{tikzpicture}

\end{document}