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and the user can define titles 18 for the histogram and each axis.
Sets of (x, y) or (x, y, z) data can be displayed and analyzed in ROOT using
the TGraph or TGraph2D classes. The data errors can also be displayed using
the derived classes TGraphErrors and TGraphAsymErrors. In addition to fitting,
the TGraph classes provide the functionality for interpolating the data points
using different techniques such as cubic splines and for smoothing.
ROOT allows the user to fit both binned and unbinned data with paramet-
ric functions which can be displayed together with the data. The plottable
functions, are represented by the classes TF1, TF2 or TF3 depending on the di-
mension. They can be created either from precompiled user code, using global
functions or class member functions or from mathematical expressions which
are handled by the TFormula class. TFormula is able to parse expressions con-
taining mathematical functions, including those in TMath and using a special
syntax for defining the parameters. Predefined expression representing func-
tions like polynomial, gaussians, exponential or landau are also available to
facilitate the usage.
In addition to invoking the Fit() method from a macro, the user can also
make use of the GUI provided by the fit panel (figure 7) during interactive
sessions. It can be opened directly from the ROOT TCanvas menu or via the
context menu of any ROOT object which is suitable for fitting, available after
a right mouse click on the object. With the fit panel, the user can select the
fit function, set the initial parameter and control all the available fit options.
It offers also the possibility to draw scan plots and contour plots of the fitted
parameters.
2.4 Graphics and User Interface
Whenever ROOT draws an object, it puts it into a TCanvas instance, repre-
senting an area mapped to a window directly under the control of the display
manager. One can save the TCanvas into several possible formats: for standard
graphics formats, publication quality is obtained by means of vector graphics
like PostScript or PDF, but raster graphics is usually a better choice for images
to be included into web pages. One can also store it as a C++ macro where
the C++ statements reproduce the state of the TCanvas and its contents. This
allows complete reproduction from within ROOT.
Of course, we can open multiple canvases if we want to display different things,
but it is often better to organize everything into a single TCanvas. For this
reason, a TCanvas instance can be subdivided into independent graphical ar-
18 LAIEX-like strings are supported.16
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Synchrotron-based high-pressure research in materials science, article, Date Unknown; (https://digital.library.unt.edu/ark:/67531/metadc929183/m1/16/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.