Plotting the frequency bandwidth

Question

I do not have almost any experience with pgfplot and I am having some problems with something which seemed really easy.

What I want to do is filling the area between a function and two vertical lines identified by the intersection of a horizontal line with the function.

I found the intersections and I could draw correctly the vertical lines but I cannot understand how to fill the area

Following there is the code I managed to produce so far.

\documentclass{article}
\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{calc,intersections}






\begin{document}

\begin{figure}
\centering
\begin{tikzpicture}
\begin{axis}[scale=1]
\addplot+[name path global=GraphCurve, domain=0.5:1.5, samples=400, color=black, mark=none]{0.09*x^2/sqrt((1-x^2)^2+(0.09*x)^2)};

\addplot+[name path global=HorizontalLine, domain=0.5:1.5,mark=none, opacity=0]{0.5};

\path[dashed,name intersections={of=GraphCurve and HorizontalLine,name=i}] (i-2)%
      \pgfextra{\pgfgetlastxy{\macrox}{\macroy}%
         \global\let\macrox\macrox};
         \def \xinta {\macrox}
 \draw[name path global=vert1, dashed](i-2) -- (\xinta,0);        
 \path (i-1)
         \pgfextra{\pgfgetlastxy{\macrox}{\macroy}%
         \global\let\macrox\macrox};
              \def \xintb {\macrox} 

\draw[name path global=vert2,dashed](i-1) -- (\xintb,0);
\coordinate [label=left:$A$](A) at (i-1);
\coordinate [label=right:$B$](B) at (i-2);


\end{axis}
\end{tikzpicture}
\caption{This picture has been created with Pgfplots}
\end{figure}

\end{document}

Can anybody help with this?

Welcome to TeX.sx! Usually, we don't put a greeting or a "thank you" in our posts. While this might seem strange at first, it is not a sign of lack of politeness, but rather part of our trying to keep everything very concise. Accepting and upvoting answers is the preferred way here to say "thank you" to users who helped you. — Peter Jansson, Apr 04 '13 at 20:06
Either TikZ CVS version or pgfplots 1.8 has issues with name path global. It doesn't recognize the names on my MikTeX machine. I'll try to check it again later. — percusse, Apr 04 '13 at 21:06
@percusse It seems that in the definition of \tikz@intersect@def, the switching from \lets to \defs is the culprit. Changing it back, and the example works again. — Qrrbrbirlbel, Apr 04 '13 at 23:02
@Qrrbrbirlbel Ah great. I should learn to diff better. I missed that. Do you mind filing a bug report for that? — percusse, Apr 05 '13 at 06:04

score 5 · Answer 1 · answered Apr 04 '13 at 20:53

I’d clip it.

Code

\documentclass[tikz]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.7}
\usetikzlibrary{calc,intersections,backgrounds}
\begin{document}
\begin{tikzpicture}
\begin{axis}
\addplot+[name path global=GraphCurve, domain=0.5:1.5, samples=400, color=black, mark=none]{0.09*x^2/sqrt((1-x^2)^2+(0.09*x)^2)};

\addplot+[name path global=HorizontalLine, domain=0.5:1.5,mark=none, opacity=0]{0.5};

\path [name intersections={of=GraphCurve and HorizontalLine,name=i}];

\draw[dashed] (i-1) coordinate[label=left:$A$] -- ({axis cs:0,0} -| i-1);
\draw[dashed] (i-2) coordinate[label=right:$B$] -- ({axis cs:0,0} -| i-2);

\begin{scope}[on background layer]
    \clip ({axis cs:0,0} -| i-1) rectangle ({axis cs:0,\pgfkeysvalueof{/pgfplots/ymax}} -| i-2);
    \addplot+ [domain=0.5:1.5, samples=400, draw=none, mark=none, fill=gray] {0.09*x^2/sqrt((1-x^2)^2+(0.09*x)^2)} \closedcycle;
\end{scope}
\end{axis}
\end{tikzpicture}
\end{document}

Output

enter image description here

Plotting the frequency bandwidth

1 Answers1

Code

Output

Linked