[Tex/LaTex] How to fill an area with fading color

fillbetweentikz-styles

I want to fill an area on a x–y plane with fading color, but have no idea how to do it. I know how to fill shapes with color, but not how to do it when the area is not a well defined shape.

Let me be more specific:
I drew a rough sketch of the implicit function y^2-x^2=a^2:

\documentclass{article}

\usepackage{tikz}

\begin{document}

        \begin{center}
        \begin{tikzpicture}
          \draw[->] (-3,0) -- (3,0) node[right] {$x$};
          \draw[->] (0,-3) -- (0,3) node[above] {$y$};

          \draw (-3,3) parabola bend (0,1.25) (3,3);
          \draw (-3,-3) parabola bend (0,-1.25) (3,-3);
        \end{tikzpicture}
        \end{center}

\end{document}

This produces the following:
enter image description here

Now I want to fill the area that enclosed between these two parabolas with a color that fades away at the right and left edges (to emphasize the fact that the area goes further away to infinity).

Can it be done?

Thanks in advanced!

Best Answer

May be you should use pgfplots which offers fill between facility. But here is a tikz version:

\documentclass{article}

\usepackage{tikz}

\begin{document}

        \begin{center}
        \begin{tikzpicture}
          \draw[thick] (-3,3) parabola bend (0,1.25) (3,3);
          \draw[thick] (-3,-3) parabola bend (0,-1.25) (3,-3);
          \fill[left color = olive!10,right color = olive!10, middle color=olive]
                (-3,3) parabola bend (0,1.25) (3,3) -- (3,-3) parabola bend (0,-1.25) (-3,-3)
                -- (-3,3) -- cycle;
          \draw[->] (-4,0) -- (4,0) node[right] {$x$};
          \draw[->] (0,-3) -- (0,3) node[above] {$y$};
        \end{tikzpicture}
        \end{center}

\end{document}

enter image description here

Using pgfplotsand its fillbetween library, your code would look something like:

\documentclass{article}
\usepackage{pgfplots}
\usepgfplotslibrary{fillbetween}
\pgfplotsset{compat=1.11}

\begin{document}

\begin{center}
\begin{tikzpicture}
\begin{axis}[
  axis lines=middle,
  xtick=\empty,
  ytick=\empty,
  ]
  \addplot[blue,name path=U] {sqrt(3^2+x^2)};
  \addplot[blue,name path=L] {-sqrt(3^2+x^2)};
  \addplot[left color=cyan!05,right color=cyan!05,middle color=cyan!80!black] 
  fill between[of=U and L,soft clip={domain=-5:5},];
\end{axis}
\end{tikzpicture}
\end{center}

\end{document}

And the result:

enter image description here

Related Solutions

[Tex/LaTex] Fill area between two lines tikz

I have rewritten this using pgfplots, which is intended for plotting data and functions (rather than TiKz which is better for schematics). Here is my initial try. You need to play a little with the options to adjust the plot to your likening.

\documentclass[mathserif]{beamer}
\usepackage{pgfplots}
\usepgfplotslibrary{fillbetween}
\pgfplotsset{compat=1.12}

\begin{document}
\vspace*{1in}
\begin{tikzpicture}
\begin{axis}[
    xlabel = Time $t$,
    xmin=-1,xmax = 9,
    hide y axis,
    axis x line=bottom,
    xticklabels={,,},
    xtick style = {draw = none},]
\node[scale=0.1] (a) at (axis cs: 1.5,1.5) {\phantom{$.$}};
\node[scale=0.1] (b) at (axis cs: 1.5,0.5) {\phantom{$.$}};
\node[scale=0.9] (c) at (axis cs: 7,3.5) {{$N_{\alpha}(t)$}};
\node[scale=0.9] (e) at (axis cs: 6,3) {{$N_d(t)$}};
\node[scale=0.1] (f) at (axis cs: 3.8,2.1) {\phantom{$.$}};
\node[scale=0.9] (g) at (axis cs: 5,1.5) {{Area $u(t)$}};
\draw[<->] (a) edge node[midway,] {{\scriptsize X($t$)}} (b);
\draw[-] (f)--(g);
\addplot[name path = A,no markers,color=blue,thick] coordinates {
(0,0)
(0,0.5)
(0.7,0.5)
(0.7,1)
(1.1,1)
(1.1,1.5)
(2,1.5)
(2,2)
(3,2)
(3,2.5)
(3.6,2.5)
(3.6,3)
(4.6,3)
(4.6,3.5)
(5.7,3.5)
};
\addplot[name path = B,no markers,color=purple,thick] coordinates {
(1,0)
(1,0.5)
(1.7,0.5)
(1.7,1)
(2.1,1)
(2.1,1.5)
(2.6,1.5)
(2.6,2)
(4,2)
(4,2.5)
(5,2.5)
(5,3)
(5.5,3)
(5.5,3.5)
(6.5,3.5) };
 \addplot[gray!50] fill between[of=A and B];
\end{axis}
\end{tikzpicture}
\end{document}

[Tex/LaTex] PGFPlots – Fill area between two curves

Since pgfplots version 1.10 you can load library fillbetween:

\documentclass{article}
\usepackage{pgfplotstable}
\pgfplotsset{compat=1.15}% current version is 1.15
\usepgfplotslibrary{fillbetween}
\usepackage{filecontents}
\begin{filecontents}{data.dat}
0 0.2
1 0.217
2 0.255
3 0.288
6 0.58
7 0.91
8 1.02
10 1.05
12 0.92
13 0.78
15 0.56
17 1.1
\end{filecontents}
\begin{filecontents}{data2.dat}
0 1.2
1 0.8
2 0.6
3 0.20
6 0.4
7 0.5
8 1.5
10 1.5
12 0.5
13 0.9
15 0.4
17 1.1
\end{filecontents}

\pgfplotstableread{data.dat}\data
\pgfplotstableread{data2.dat}\datas

\begin{document}
\begin{tikzpicture}
  \begin{axis}[
      xlabel=Time of day,
      ylabel=Volume,
      ytick=\empty,
      axis x line=bottom,
      axis y line=left,
      enlargelimits=true
    ]
  \addplot[name path=plot1,blue,line width=2pt,mark=*] table {\data};
  \addplot[name path=plot2,red,line width=2pt,mark=*]  table {\datas};
  \addplot fill between[ 
    of = plot1 and plot2, 
    split, % calculate segments
    every even segment/.style = {yellow!20!white},
    every odd segment/.style ={gray!20!white}
  ]; 
  \end{axis}
\end{tikzpicture}
\end{document}

results in

If axis background can be filled white and you only want to color the areas yellow where the red curve is higher than the blue one, you could use

\documentclass{article}
\usepackage{pgfplotstable}
\pgfplotsset{compat=1.15}% current version is 1.15
\usepgfplotslibrary{fillbetween}
\usepackage{filecontents}
\begin{filecontents}{data.dat}
0 0.2
1 0.217
2 0.255
3 0.288
6 0.58
7 0.91
8 1.02
10 1.05
12 0.92
13 0.78
15 0.56
17 1.1
\end{filecontents}
\begin{filecontents}{data2.dat}
0 1.2
1 0.8
2 0.6
3 0.288
4 1
6 0.4
7 0.5
8 1.5
10 1.5
12 0.5
13 0.9
15 0.4
17 1.1
\end{filecontents}

\pgfplotstableread{data.dat}\data
\pgfplotstableread{data2.dat}\datas

\begin{document}
\begin{tikzpicture}
  \begin{axis}[
      xlabel=Time of day,
      ylabel=Volume,
      ytick=\empty,
      axis x line=bottom,
      axis y line=left,
      enlargelimits=true,
      axis background/.style={fill=white}
    ]
  \addplot[name path=plot1,blue,line width=2pt,mark=*] table {\data};
  \addplot[name path=plot2,red,line width=2pt,mark=*]  table {\datas};
  \path[name path=xaxis](current axis.south west)--(current axis.south east);
  \addplot[yellow!20!white] fill between[ 
    of = plot1 and plot2,
    split
  ];
  \addplot[axis background] fill between[of = plot1 and xaxis];
  \end{axis}
\end{tikzpicture}
\end{document}

results in (I have changed some values in the data files)

Unfortunaly I did not find a solution where the areas with a higher red curve can be colored yellow and that one with a lower red curve can be colored gray in the same picture.

Best Answer

Related Solutions

[Tex/LaTex] Fill area between two lines tikz

[Tex/LaTex] PGFPlots – Fill area between two curves

Related Question