source: trunk/documents/UserDoc/DocBookUsersGuides/IntroductionToGeant4/xml/Introduction/ChapIntroduction.xml @ 1358

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<!-- ******************* Chapter **************************** -->
<chapter id="chap.G4Scope">
<title>
Geant4 Scope of Application
</title>

<para>
Geant4 is a free software package composed of tools which can be
used to accurately simulate the passage of particles through
matter. All aspects of the simulation process have been included in
the toolkit:

<itemizedlist spacing="compact">
  <listitem><para>
    the geometry of the system,
  </para></listitem>
  <listitem><para>
    the materials involved,
  </para></listitem>
  <listitem><para>
    the fundamental particles of interest,
  </para></listitem>
  <listitem><para>
    the generation of primary events,
  </para></listitem>
  <listitem><para>
    the tracking of particles through materials and electromagnetic fields,
  </para></listitem>
  <listitem><para>
    the physics processes governing particle interactions,
  </para></listitem>
  <listitem><para>
    the response of sensitive detector components,
  </para></listitem>
  <listitem><para>
    the generation of event data,
  </para></listitem>
  <listitem><para>
    the storage of events and tracks,
  </para></listitem>
  <listitem><para>
    the visualization of the detector and particle trajectories, and
  </para></listitem>
  <listitem><para>
    the capture and analysis of simulation data at different levels
    of detail and refinement.
  </para></listitem>
</itemizedlist>
</para>

<para>
Users may construct stand-alone applications or applications built
upon another object-oriented framework. In either case the toolkit
will support them from the initial problem definition to the
production of results and graphics for publication. To this end,
the toolkit includes:

<itemizedlist spacing="compact">
  <listitem><para>
    user interfaces,
  </para></listitem>
  <listitem><para>
    built-in steering routines, and
  </para></listitem>
  <listitem><para>
    command interpreters
  </para></listitem>
</itemizedlist>

which operate at every level of the simulation.
</para>

<para>
At the heart of Geant4 is an abundant set of physics models to
handle the interactions of particles with matter across a very wide
energy range. Data and expertise have been drawn from many sources
around the world and in this respect, Geant4 acts as a repository
which incorporates a large part of all that is known about particle
interactions.
</para>

<para>
Geant4 is written in C++ and exploits advanced
software-engineering techniques and object-oriented technology to
achieve transparency. For example, the way in which cross sections
are input or computed is separated from the way in which they are
used or accessed. The user can overload both of these features.
Similarly, the computation of the final state can be divided into
alternative or complementary models, according to the energy range,
the particle type, and the material. To build a specific
application the user-physicist chooses from among these options and
implements code in user action classes supplied by the toolkit. A
serious problem with previous simulation codes was the difficulty
of adding new or variant physics models; development was difficult
due to the increased size, complexity and interdependency of the
procedure-based code. In contrast, object-oriented methods help
manage complexity and limit dependencies by defining a uniform
interface and common organizational principles for all physics
models. Within this framework the functionality of models can be
more easily recognized and understood, and the creation and
addition of new models is a well-defined procedure that entails
little or no modification to the existing code. 
</para>

</chapter>


<!-- ******************* Chapter **************************** -->
<chapter id="chap.HistoryG4">
<title>
History of Geant4
</title>

<para>
These ideas first appeared in two studies done independently at
CERN and KEK in 1993. Both groups sought to investigate how modern
computing techniques could be applied to improve the existing
FORTRAN based Geant3 simulation program. Activities were merged in
the fall of 1994 and a formal proposal, RD44, to construct an
entirely new program based on object-oriented technology was
submitted to CERN's Detector Research and Development Committee.
The initiative grew to become a large international collaboration
of physicist programmers and software engineers from a number of
institutes and universities participating in a range of high-energy
physics experiments in Europe, Japan, Canada and the United States.
The objective was to write a detector simulation program which had
the functionality and flexibility necessary to meet the
requirements of the next generation of subatomic physics
experiments. The initial scope quickly widened when it became
apparent that such a tool would also benefit the nuclear,
accelerator, space and medical physics community, with more
individuals joining from these fields of science.
</para>

<para>
The RD44 project represented a pioneering effort in redesigning
a major CERN software package for a modern object-oriented (OO)
environment based on C++. The R&amp;D phase was completed in
December 1998 with the delivery of the first production release.
The collaboration was subsequently renamed Geant4 and reinstated on
the basis of a formal Memorandum of Understanding (MoU) signed by
many of the same national institutes, laboratories and large HEP
experiments who participated in RD44. The agreement addresses the
program management, maintenance and user support during the
production phase and the continued development and refinement of
the toolkit. It is subject to tacit renewal every two years and
sets out a collaboration structure defined by a Collaboration Board
(CB), a Technical Steering Board (TSB) and several working
groups. In February 2006 a new MoU came into effect and CB and TSB
were renamed to Oversight Board (OB) and Steering Board (SB) 
respectively. 
</para>

<para>
The collaboration now profits from the accumulated experience of
many contributors to the field of Monte Carlo simulation of physics
detectors and physical processes. While geographically distributed
software development and large-scale object-oriented systems are no
longer a novelty, Geant4, in terms of the size and scope of the
code and the number of contributors, may well represent the largest
and most ambitious project of its kind outside the corporate world.
A clean overall problem decomposition has led to a clear
hierarchical structure of domains. Every section of the Geant4
software, which corresponds to a releasable component (library), is
individually managed by a working group of experts. In addition,
there is a working group for each of the activities: testing and
quality assurance, software management and documentation
management. A release coordinator heads each group. This consequent
distribution of responsibility among a relative large number of
people permits a support structure whereby outside users can
address questions directly to the appropriate expert. 
</para>

</chapter>


<!-- ******************* Chapter **************************** -->
<chapter id="chap.OverviewG4Func">
<title>
Overview of Geant4 Functionality
</title>

<para>
The Geant4 class category diagram is shown in <xref linkend="fig.G4ClassCategory" />
</para>

<para>
Categories at the bottom of the diagram are used by virtually
all higher categories and provide the foundation of the
toolkit.
</para>

<para>
The

<itemizedlist spacing="compact">
  <listitem><para>
    <emphasis>global</emphasis>
  </para></listitem>
</itemizedlist>

category covers the system of units, constants, numerics and random
number handling.
</para>

<para>
The two categories:

<itemizedlist spacing="compact">
  <listitem><para>
    <emphasis>materials</emphasis>
  </para></listitem>
  <listitem><para>
    <emphasis>particles</emphasis>
  </para></listitem>
</itemizedlist>

implement facilities necessary to describe the physical properties
of particles and materials for the simulation of particle-matter
interactions.
</para>

<para>
The

<itemizedlist spacing="compact">
  <listitem><para>
    <emphasis>geometry</emphasis>
  </para></listitem>
</itemizedlist>

module offers the ability to describe a geometrical structure and
propagate particles efficiently through it.
</para>

<figure id="fig.G4ClassCategory">
<title>
Geant4 class categories
</title>

<mediaobject>
  <imageobject role="fo">
    <imagedata fileref="./AllResources/Fundamentals/classCategory.jpg"
               format="JPG" contentwidth="7.0cm" align="center" />
  </imageobject>
  <imageobject role="html">
    <imagedata fileref="./AllResources/Fundamentals/classCategory.jpg"
               format="JPG" align="center" />
  </imageobject>
</mediaobject>
</figure>

<para>
Above these reside categories required to describe the tracking
of particles and the physical processes they undergo. The

<itemizedlist spacing="compact">
  <listitem><para>
    <emphasis>track</emphasis>
  </para></listitem>
</itemizedlist>

category contains classes for tracks and steps, used by the

<itemizedlist spacing="compact">
  <listitem><para>
    <emphasis>processes</emphasis>
  </para></listitem>
</itemizedlist>

category, which contains implementations of models of physical
interactions: electromagnetic interactions of leptons, photons,
hadrons and ions, and hadronic interactions.
</para>

<para>
All processes are invoked by the

<itemizedlist spacing="compact">
  <listitem><para>
    <emphasis>tracking</emphasis>
  </para></listitem>
</itemizedlist>

category, which manages their contribution to the evolution of a
track's state and provides information in sensitive volumes for
hits and digitization.
</para>

<para>
Above these the

<itemizedlist spacing="compact">
  <listitem><para>
    <emphasis>event</emphasis>
  </para></listitem>
</itemizedlist>

category manages events in terms of their tracks and the

<itemizedlist spacing="compact">
  <listitem><para>
    <emphasis>run</emphasis>
  </para></listitem>
</itemizedlist>

category manages collections of events that share a common beam and
detector implementation. A

<itemizedlist spacing="compact">
  <listitem><para>
    <emphasis>readout</emphasis>
  </para></listitem>
</itemizedlist>

category allows the handling of pile-up.
</para>

<para>
Finally capabilities that use all of these categories and
connect to facilities outside the toolkit through abstract
interfaces, provide <emphasis>visualization</emphasis>, 
<emphasis>persistency</emphasis> and user 
<emphasis>interface</emphasis> capabilities.
</para>

</chapter>


<!-- ******************* Chapter **************************** -->
<chapter id="chap.G4UserSupport">
<title>
Geant4 User Support
</title>

<para>
The collaboration offers support for Geant4, providing

<itemizedlist spacing="compact">
  <listitem><para>
    assistance with problems relating to the code,
  </para></listitem>
  <listitem><para>
    consultation on using the toolkit, and
  </para></listitem>
  <listitem><para>
    response to enhancement requests.
  </para></listitem>
</itemizedlist>
</para>

<para>
A user can also expect assistance in

<itemizedlist spacing="compact">
  <listitem><para>
    investigating aberrant results.
  </para></listitem>
</itemizedlist>
</para>

<para>
Users of the software who encounter a problem in running the code
can use an

<itemizedlist spacing="compact">
  <listitem><para>
    Internet-based 
    <ulink url="http://geant4.web.cern.ch/geant4/problemreport/">
    problem reporting system
    </ulink>.
  </para></listitem>
</itemizedlist>
</para>

<para>
The system is open to all users. It is set up automatically to
assign problem reports to the responsible person according to the
category affected. The contact person may then respond directly or
forward it to a colleague. This system is a customized version of
the open source reporting tool 
<ulink url="https://bugzilla.mozilla.org/">
Bugzilla
</ulink>
. 
Besides routing the
problem to specialists, it tracks and documents the responses until
the problem is resolved.
</para>

<para>
New requirements, such as requests for new functionality, are
presented to and decided by the Steering Board (SB). The
SB sets the priorities and agrees on time-scales for the
fulfillment of new requirements. Such support is guaranteed to
collaboration members, while requests from non-members are handled
on a <emphasis>best effort</emphasis> basis.
</para>

<para>
For each member organisation a contact person 
<ulink url="http://geant4.web.cern.ch/geant4/collaboration/SteeringBoard.shtml">
(SB member)
</ulink>
has been designated who acts as a first reference for
Geant4 users in that locality, which may include affiliated
institutions, user groups, and others in the same geographic area.
The contact person will respond to enquiries, help resolve simple
problems, and forward more specialized queries to the relevant
expert(s).
</para>

<para>
Beyond that, a list of frequently asked questions 
<ulink url="http://geant4.web.cern.ch/geant4/support/faq.shtml">
(FAQs)
</ulink>
, 
and an internet-based 
<ulink url="http://geant4-hn.slac.stanford.edu:5090/Geant4-HyperNews/index">
user forum
</ulink>
complete the available Geant4 user support.
</para>

</chapter>


<!-- ******************* Chapter **************************** -->
<chapter id="sect.SoftwareKnowledge">
<title>Software Knowledge Required to Use the Geant4 Toolkit
</title>

<para>
In general, there are three types of users:

<itemizedlist spacing="compact">
   <listitem><para>
     the <emphasis role="bold">end user</emphasis>,
   </para></listitem>
   <listitem><para>
     the <emphasis role="bold">application programmer</emphasis>,
   </para></listitem>
</itemizedlist>

and for large simulation tasks:

<itemizedlist spacing="compact">
  <listitem><para>
    the <emphasis role="bold">framework provider</emphasis>.
  </para></listitem>
</itemizedlist>
</para>

<para>
The <emphasis role="bold">end user</emphasis> runs the simulation 
program by controlling run time parameters. The interface with the 
program may be a graphical user interface, an interactive command 
line interface, or the macro-based system for batch. The end user 
needs a basic knowledge of how to control the program flow but does 
not necessarily have to know object-oriented programming or C++.
</para>

<para>
The <emphasis role="bold">application programmer</emphasis> is central 
to any simulation task. A firm knowledge of C++ is required to implement 
code in user action classes to specify, at a minimum, the detector description,
the relevant particles and physics processes, and the initial event
kinematics. A manual for the application programmer is found in the
<ulink url="http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/ForApplicationDeveloper/html/index.html">
User's Guide: For Application Developers
</ulink>
.
</para>

<para>
Using standard components of Geant4, a 
<emphasis role="bold">framework provider</emphasis>
would add interfaces to external tools, such as for example, to
Computer Aided Design (CAD) programs, Object-Oriented Data Base
Management Systems (ODBMS) and graphics systems. This requires the
development of new classes overloading standard Geant4
functionality and hence a solid understanding of object-oriented
Programming. A manual for the framework provider is found in the
<ulink url="http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/ForToolkitDeveloper/html/index.html">
User's Guide: For Toolkit Developers
</ulink>
.
</para>

<para>
<emphasis role="bold">References</emphasis>
</para>

<para>
All user documentation can be found on the Geant4 homepage
<ulink url="http://cern.ch/geant4">
http://cern.ch/geant4
</ulink>
.
</para>

<para>
References for Object-Oriented Technology:

<itemizedlist spacing="compact">
  <listitem><para>
    Grady Booch, Object-Oriented Analysis and Design with
    Applications The Benjamin/Cummings Publishing Co. Inc, 1994, ISBN
    0-8053-5340-2
  </para></listitem>
  <listitem><para>
    R.C.Martin, Designing Object-Oriented C++ Applications Using
    The Booch Method, Prentice Hall 1995, ISBN 0-13-203837-4;
  </para></listitem>
  <listitem><para>
    E. Gamma, et al., Design Patterns - Elements of Reusable
    Object-Oriented Software, Addison Wesley 1995, ISBN
    0-201-63361-2;
  </para></listitem>
</itemizedlist>
</para>

<para>
References for C++:

<itemizedlist spacing="compact">
  <listitem><para>
    B.Stroustrup, C++ Programming Language 3rd Edition, Addison
    Wesley, ISBN: 0-201-88954-4
  </para></listitem>
  <listitem><para>I.Pohl, Object-Oriented Programming Using C++, 2nd Edition,
    Addison Wesley, ISBN: 0-201-89550-1.
  </para></listitem>
</itemizedlist>
</para>

</chapter>


<!-- ******************* Chapter **************************** -->
<chapter id="sect.ComputingEnv">
<title>
Computing Environment Required by the Geant4 Toolkit
</title>

<para>
The Geant4 toolkit is available for a variety of operating systems:

<itemizedlist spacing="compact">
  <listitem><para>
    flavors of UNIX,
  </para></listitem>
  <listitem><para>
    Linux,
  </para></listitem>
  <listitem><para>
    and Windows systems.
  </para></listitem>
</itemizedlist>
</para>

<para>
In order to link and build the program only two underlying software
packages are mandatory:

<itemizedlist spacing="compact">
  <listitem><para>
    CLHEP (Class Library of High Energy Physics) and the
  </para></listitem>
  <listitem><para>
    STL (Standard Template Library for fundamental classes like C++
    containers and strings).
  </para></listitem>
</itemizedlist>
</para>

<para>
The Geant4 source code is available from the 
<ulink url="http://geant4.web.cern.ch/geant4/">
Geant4 web pages
</ulink>
while CLHEP is available from the 
<ulink url="http://proj-clhep.web.cern.ch/proj-clhep/">
CLHEP Home Page
</ulink>
. 
For details on setting up the computing environment see the 
<ulink url="http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/InstallationGuide/html/index.html">
Installation Guide
</ulink>
.
</para>

</chapter>