\section{Chart::ErrorBars}
\herv{Name:} Chart::ErrorBars\\ \\
\herv{File:} ErrorBars.pm\\ \\
\herv{Requires:}Chart::Base, GD, Carp, FileHandle\\ \\
\herv{Description:} \fett{ErrorBars} is a \fett{subclass} of Chart::Base.\\
The class ErrorBars creates a point chart with error bars.\\
Chart expects the error values within the data array. By use of the add\_dataset method the error values are the two next sets after the y values. The first set after the y values has to be a set values for the upper error bars. The next set is an array of the down errors.\\
If you want to use the same value for the up and down error, then you have to set the 'same\_error' option to 'true'. In this case only one set after the y values is interpreted as a set of errors.\\
Of course, it's also possible to use the add\_pt method in a respective way.\\
\\  
\herv{Example:}
\begin{figure}[h]
	\begin{center}
		\includegraphics[scale=0.7]{error.png}
	\end{center}
	\caption{Error bars chart}
	\label{fig:error}
\end{figure}
\begin{verbatim}
use Chart::ErrorBars;
$g = Chart::ErrorBars->new();

#the x values
$g->add_dataset(qw(1   1.1  1.2  1.3  1.4  1.5  1.6  1.7  1.8  1.9  2
                   2.1 2.2  2.3  2.4  2.5));
#the y values
$g->add_dataset(qw(1   1.1  1.2  1.1  1.14 1.15 1.26 1.2  1.1  1.19 1.2
                   1.4 1.6  2.0  2.5  3.1));
#the up errors
$g->add_dataset(qw(0.4 0.1  0.2  0.1  0.14 0.15 0.26 0.27 0.1  0.19 0.2
                   0.1 0.1  0.2  0.1  0.3));
#the down errors
$g->add_dataset(qw(0.2 0.11 0.12 0.11 0.2  0.3  0.12 0.27 0.11 0.3  0.2
                   0.2 0.2  0.1  0.1  0.2));
                   
$g->set( 'xy_plot' => 'true',
         'precision' => 1,
         'pt_size' =>10, 'brush_size' => 2,
         'legend' => 'none',
         'title' => 'Error Bars Demo',
         'grid_lines' => 'true');

$g->png("errorbars.png");
\end{verbatim}
\herv{Constructor:} An instance of a error bars chart object can be created with the constructor new():\\
\fett{\$obj = Chart::ErrorBars->new();}\\
\fett{\$obj = Chart::ErrorBars->new(\kursiv{width}, \kursiv{height});}\\
\\
If \fett{new} has no arguments, the constructor returns an image with the size 300x400 pixels. If new has two arguments \kursiv{width} and \kursiv{height}, it returns an image with the desired size. \\ 
\\ 
\herv{Methods:}All universally valid methods, see page \pageref{methods}: Chart::Base. \\
\\
\herv{Attributes/Options:} All universally valid options, see page \pageref{options}. Also available these special options:
\begin{description}
\item['same\_error'] Tells chart that you want to use the same error value of a data point if set to true. Then you have to add just one set of error values. Defaults to 'false'.
\item['y\_axes'] Tells chart where to place the y-axis. Valid values are 'left', 'right' and 'both'. Defaults to 'left'.
\item['pt\_size']Sets the radius of the points in pixels. Default is 18.
\item['brush\_size']Sets the width of the lines in pixels. Default is 6.
\item['xy\_plot']Forces Chart to plot a x-y-graph, which means that the x-axis is also numeric if set to 'true'. Very useful for plots of mathematical functions. Defaults to 'false'.
\item['sort']Sorts the data of a x-y-graph ascending if set to 'true'. Should be set if the added data isn't sorted. Defaults to 'false'. 
\end{description}