# How do I group curves in 2-D plots with pgfplots

In the above image, you can see that there are 4 curves. I have two techniques (black and red). I test them on two different experimental scenarios. So corresponding to each scenario, I get one red and black curve each. I want to point out that one set of black and red curve belong to one experimental scenario. Hope that clears it. While I am familiar with plotting this curves in pgfplots using the given data, I can't figure how to group them as shown in the image. The plot was generated using matlab.

• How do I group curves in a given pgfplot?
• In your opinion, are there better ways on grouping curves in a plot?
• By "grouping", do you mean the circles around the plots? – Jake Sep 27 '13 at 9:32
• that is one way of looking at it. I have two techniques (black and red). I test them on two different experimental scenarios. So corresponding to each scenario, I get one red and black curve each. I want to point out that one set of black and red curve belong to one experimental scenario. Hope that clears it. – dineshdileep Sep 28 '13 at 0:41

Since don't have your MWE, I will use two simple curves to illustrate the idea for group annotation. Here, axis cs for annotation is used, where two nodes are defined for ellipse and pin annotation respectively. The actual coordinates are supposed to be determined by the users according to their needs.

\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{compat=1.3}

\tikzstyle{every pin}=[->, fill=white,draw=black,font=\footnotesize]

\begin{document}
\begin{tikzpicture}
\begin{axis}