pgfplots: Fill area delimited by 3 graphs

Question

I have the following function plot:

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.13}
\begin{document}
\begin{tikzpicture}
\begin{axis}[domain=0:0.8, ymin=0, ymax=2]
\addplot[color=blue, smooth, thick, samples=50] {1-2*x^2};
\addplot[color=red, smooth, thick, samples=50] {2-5*x^2};
\addplot[color=black, smooth, thick, samples=50] {3-30*x^2};
\end{axis}
\end{tikzpicture}
\end{document}

Now I want to gray the area delimited by those 3 graphs, based on an automated computation of the intersection points, possibly using the fillbetween library. The solutions to similar questions I found do not work here, because we have 3 graphs involved (and not only two). Also, I'm interested in a clean solution that generalizes to analogous situations involving more than 3 graphs.

Does this answer your question? Fill space between three \draw lines with arbitrary intersection points — Pier Paolo, Nov 27 '22 at 18:50
@PierPaolo Thank you for the pointer; it might be helpful indeed. However, the setting is a bit different. The other question it about paths in a pure tikz picture; here I have the paths given by pgfplot functions. It still would be great to have an answer adapted for this pgfplots setting, for people like me who are not too fluent in tikz/pgfplots. — azimut, Nov 27 '22 at 19:37

score 2 · Accepted Answer · answered Nov 27 '22 at 19:45

\documentclass[border=5mm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usepgfplotslibrary{fillbetween}
\begin{document}
    \begin{tikzpicture}
        \begin{axis}[domain=0:0.8, ymin=0, ymax=2]
            \addplot[draw=none,smooth,samples=50,name path=A] {1-2*x^2};
            \addplot[draw=none,smooth,samples=50,name path=B] {2-5*x^2};
            \addplot[draw=none,smooth,samples=50,name path=C] {3-30*x^2};
            \begin{scope}
                \clip[intersection segments={of=A and B, sequence={L1 -- R1[reverse]}}];
                \fill[gray!20,intersection segments={of=B and C, sequence={L2[reverse] -- R2}}];
            \end{scope}
            \addplot[color=blue, smooth, thick, samples=50] {1-2*x^2};
            \addplot[color=red, smooth, thick, samples=50] {2-5*x^2};
            \addplot[color=black, smooth, thick, samples=50] {3-30*x^2};
        \end{axis}
    \end{tikzpicture}
\end{document}

Many thanks for this answer! It works. Would you mind adding a short explanation? Why the scope is needed, and what does the \clip command (I've never seen it before). — azimut, Nov 27 '22 at 20:12
@azimut Without scope the \clip command clips all subsequent drawing. For the \clip command see tikz manual “2.11 Clipping a Path” p. 37 — polyn, Nov 27 '22 at 20:47

score 1 · Answer 2 · answered Nov 27 '22 at 17:41

1

Like this:

Code:

\documentclass{book}
\usepackage{pgfplots}
\usepgfplotslibrary{fillbetween} % <-- this does the trick
\begin{document}
    \begin{tikzpicture}
        \begin{axis}[domain=0:0.8, ymin=0, ymax=2]
            \addplot[color=blue, smooth, thick, samples=50,name path=A] {1-2x^2};
            \addplot[color=red, smooth, thick, samples=50,name path=B] {2-5x^2};
            \addplot[color=black, smooth, thick, samples=50,name path=C] {3-30*x^2};
            \addplot[cyan!50] fill between [of=C and B,soft clip={domain=.2:.267}];
            \addplot[cyan!50] fill between [of=A and B,soft clip={domain=.267:.577}];
        \end{axis}
    \end{tikzpicture}
\end{document}

answered Nov 27 '22 at 17:41

Raffaele Santoro

9,702

Many thanks for your answer. It looks good, but in the code I see the values .2, .267 and .577. I guess you have computed the x values of the intersection points manually. As written in my question, I'm really looking for a solution with "automated computation of the intersection points". – azimut Nov 27 '22 at 18:15
@azimut I searched for a while but I dont find nothing for this. I hope You find better things... – Raffaele Santoro Nov 27 '22 at 18:25

pgfplots: Fill area delimited by 3 graphs

2 Answers2