deletions | additions       diff --git a/Built in functionality.tex b/Built in functionality.tex  index 2957f3b..27d7ca6 100644  --- a/Built in functionality.tex  +++ b/Built in functionality.tex 
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The user starts a fitting session by opening the Fitting Tool component on the Iris desktop. The SED Viewer updates with an overplotted, unfit powerlaw model, and a plot of the residuals shown below the data. The user removes the powerlaw component, and adds four models from the Preset Components provided by Sherpa: two logarithmic parabolas (\texttt{logparabola}s) for the radio synchrotron and inverse Compton radiation and two blackbodies (\texttt{blackbody}s) for the hot dust and accretion disk. The models are added to the Components field, where the model parameter values are displayed. Double-clicking a component allows you to edit the parameters, e.g. freeze and thaw parameters, reset their initial values, and set their minimum and maximum values.   In the Model Expression field, the components are combined in arbitrary ways. Each component is given an ID which is used to reference the component in the Model Expression field. The user can also set the data ranges to be fit. In this example, we linearly combine the models, adding and fitting them one-by-one, defining the data ranges for each component (Figure \ref{fig:fitting}a, component,  then freezing the component afterwards. For each fit, we use Neldermead optimization and least squares as the statistic. We thaw all components and refit the entire SED; the result is shown in Figure \ref{fig:fitting}b. \ref{fig:fitting1}.  The user saves the fit results to a text file, showing the fit statistics, model used, and the best-fit parameter values. She can also save an XML-style file of the model that can be re-read into Iris and fit to other SED data.