tikz-pgftikz-styles
I am looking to create the graph for the function y = 1/x for x > 0. The area under the curve between x = a and x = 1 is A1. The area under the
curve between x = 1 and x = b is A2.
I don't know how to shade the regions as shown in the figure.
This is explained in the sections “15.4 Filling a Path” and “19 Plots of Functions” in the TikZ manual (numbers refer to the 2.10 version).
A simple example (note that \x r interprets \x as radians; the TikZ's sin function takes degrees as input):
\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\fill[fill=red] (pi/4,0) -- plot [domain=pi/4:3*pi/4] (\x,{sin(\x r)}) -- (3*pi/4,0) -- cycle;
\draw plot[domain=0:pi] (\x,{sin(\x r)});
\draw[gray,->] (-0.3,0) -- (pi+0.3,0);
\end{tikzpicture}
\end{document}
Here is a suggestion. I modified \vasymptote to have a second mandatory argument that is a name for the path. I then used name intersections to give node names to the various intersections between the lines, and finally used \fill to add the colour. I used the backgrounds library to add this fill on the background layer, avoiding partial covering of the plot lines.
In addition I suggest you not write the first two legend entries in math mode, and the subscripts in the two last legend entries in an upright font.
\documentclass[border=10mm]{standalone}
\usepackage{pgfplots}
\usepackage{tkz-fct}
\usetikzlibrary{intersections,backgrounds}
\newcommand{\vasymptote}[3][]{
\draw [densely dashed,name path=#3,#1] ({rel axis cs:0,0} -| {axis cs:#2,0}) -- ({rel axis cs:0,1} -| {axis cs:#2,0});
}
\newcommand{\gettikzxy}[3]{%
\tikz@scan@one@point\pgfutil@firstofone#1\relax
\edef#2{\the\pgf@x}%
\edef#3{\the\pgf@y}%
}
\pgfplotsset{
every axis/.append style={
scale only axis,
width=1.0\columnwidth,
},
/tikz/every picture/.append style={
trim axis left,
trim axis right,
}
}
\def\Dimline[#1][#2][#3][#4]{
\begin{scope}[thin, >=stealth'] % redefine as flechas
\draw let \p1=#1, \p2=#2, \n0={veclen(\x2-\x1,\y2-\y1)} in [|<->|,
decoration={markings,mark=at position .5 with {\node[#3] at (0,0)
{#4};},
},
postaction=decorate] #1 -- #2 ;
\end{scope}
}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
xmin = 0, xmax = 1000,
ymin = 12, ymax = 16,
xlabel=$Q$,
ylabel=$P$,
]
\addplot[name path global=supply, domain=0:1000, red] { 0.00325*x + 12.5125 };
\addplot[name path global=demand, domain=0:1000, blue] { -0.013*x + 22.75 };
\addplot[name path global=world, domain=0:1000, black] { 13 };
\addplot[name path global=tariff, domain=0:1000, green] { 13.65 };
\node at (axis cs:100, 13.3) {$A$};
\node at (axis cs:300, 13.3) {$B$};
\node at (axis cs:550, 13.3) {$C$};
\node at (axis cs:720, 13.1) {$D$};
\vasymptote[dashed]{350}{first}
\vasymptote[dashed]{700}{second}
\legend{Supply, Demand, $P_\mathrm{world}$, $P_\mathrm{tariff}$}
\path [name intersections={of=supply and world, by={a}},
name intersections={of=supply and tariff, by={b}},
name intersections={of=first and world, by={c}},
name intersections={of=second and world, by={d}},
name intersections={of=demand and tariff, by={e}},
name intersections={of=demand and world, by={f}}];
\begin{scope}[on background layer]
\fill [blue,opacity=.3] (axis cs:0,13) -- (axis cs:0,13.65) -- (b) -- (a) -- cycle;
\fill [red,opacity=.3] (a) -- (b) -- (c) -- cycle;
\fill [green,opacity=.3] (b) -- (c) -- (d) -- (e) -- cycle;
\fill [purple,opacity=.3] (e) -- (d) -- (f) -- cycle;
\end{scope}
\end{axis}
\end{tikzpicture}
\end{document}
Best Answer
Most of this is from the example on the bottom of p. 103 of the manual, and the positioning of
xandyis from this answer.