Domenico Tiziani / gammalib

New Features and Important Changes in GammaLib 00-07-00

Author(s) : Juergen Knoedlseder

December, 18th, 2012


1. Introduction
---------------
This document briefly summarizes module by module the most important
changes made since the last release of GammaLib.


2. Configuration
-----------------
Dependency tracking has been enabled for the Python interface files,
so that the Python wrappers will be regenerated automatically upon
modification of the interface files.


3. Application module
---------------------
File locking failures do no longer throw exceptions. This allows to
operate GammaLib also on systems that do not support file locking.
Unsupported file locking may occur on some file systems.

The GPar class now handles special values for integer and floating point
parameters, such as INDEF, NONE, UNDEF, UNDEFINED (for an undefined value)
and INF, INFINITY, NAN (for values that are not a number). If presence
of these values can be checked using the isundefined() and the
isnotanumber() methods. An isvalid() method has been added to check also
if a parameter value is valid.


4. Base module
--------------
This new module was introduced to implement interface classes that are
used to define standard interfaces for GammaLib classes. 

The basis of most classes is the GBase class. This class requires the
clear, clone, and print methods to be present. The ostream and GLog
functions are now also implement at the GBase level, hence classes do 
not need to implement the output streamers anymore. Classes that do not
derive from GBase are essentially internal classes that are not expected
to be used by a GammaLib user.

Another fundamental class is GRegistry, from which all registries are
derived.


5. FITS I/O Interface
---------------------
FITS images are now opened using their equivalent data type. This
ensures that the class that will be used to hold the data has the
correct precision that avoids data truncation.


6. Linear algebra module
------------------------
None


7. Model module
---------------
The GSkyModel class has been adapted to the new IRF interface.

The mc(), flux() and eflux() methods have been implement now for all
spectral models. In particular, simulation of an exponentially cut
off power law is now possible. The methods now also verify that the
minimum energy is smaller than the maximum energy. Otherwise, an
exception is thrown.

The new spectral model GModelSpectralLogParabola has been implemented
to describe a source with log parabola spectrum. The XML definition
is compliant with that of Fermi-LAT.


8. Numerics module
------------------
None


9. Observation module
---------------------
Added the class GSource which defines a gamma-ray source. This class was
mainly introduced to simplify the instrument response interface, and
regroups all attributes that are relative to a gamma-ray source. For the
moment those comprise the source name, the spatial model, the photon
energy and the photon arrival time.

A new interface has been defined for all public response function that
replaces all observed attributes in the interface by the GEvent class
and all true source attributes by either GPhoton or GSource. This
considerably reduces the number of interface parameters, allows for an
easy and transparent interface extension, and prepares the path for
optimizations.

The GPhotons photon container class has been added. It replaces the
old std::vector<GPhoton> GPhotons typedef that was used formerly to
implement a photon container.

The GTime interface has been reworked. GTime now stores time in a reference
that is native to GammaLib. The zero point of GammaLib's time has been
defined as January 1, 2010, 00:00:00 (TT). Times are stored in seconds,
and the time system is Terrestrial Time (TT). Conversion methods are
provided to transform GTime times into any arbitrary time reference. A
time reference is implemented using the GTimeReference class. 

The GGti class now stores the time reference, so that GTI's can be read
and written in any arbitrary time reference. In storage, however, GGti
stores all time using GTime objects, i.e. storage is in the native
GammaLib time reference.


10. Optimization module
-----------------------
None


11. Sky module
--------------
None


12. Support module
------------------
GNodeArray computations have been optimized in that the last interpolation
result is cached, and reused if the same value is requested in a subsequent
call. An unnecessary if statement has also been removed from the bi-section
method.

Unit tests have been added to check the GNodeArray class. In particular,
the linear and non-linear interpolation and extrapolation code is now
validated.


13. XML module
--------------
None


14. Test module
---------------
None


15. Multi-wavelength interface
------------------------------
The MWL response was adapted to the new response interface.


16. Fermi-LAT interface
----------------------
The Fermi-LAT response was adapted to the new response interface.

The event list reader now takes care of the time conversion from the
Fermi-LAT time reference to the GammaLib time reference.


17. CTA interface
-----------------
The CTA response class was refactored. Separate classes have been defined
to deal with the effective area (GCTAAeff), the point spread function
(GCTAPsf) and the energy dispersion (GCTAEdisp). Various response formats
are implemented by derived classes from these abstract base classes.
This allows now an easy adaption and extension of the response classes.

The CTA response was also adapted to the new response interface.

The CTA event list reader now takes care of the time conversion from the
CTA time reference to the GammaLib time reference.


18. COMPTEL interface
-----------------
An interface has been added to deal with data from the COMPTEL telescope
aboard CGRO. The interface reads the FITS files provides from HEASARC.