source: trunk/documents/UserDoc/DocBookUsersGuides/ForApplicationDeveloper/xml/TrackingAndPhysics/cutsPerRegion.xml @ 1345

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<!--  [History]                                               -->
<!--    Created by: Makoto Asai,       14-Apr-2003            -->
<!--    Converted to DocBook: Katsuya Amako, Aug-2006         -->
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<!-- ******************* Section (Level#1) ****************** -->
<sect1 id="sect.CutReg">
<title>
Cuts per Region
</title>


<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.CutReg.Gene">
<title>
General Concepts
</title>

<para>
Beginning with Geant4 version 5.1, the concept of a region has been
defined for use in geometrical descriptions. Details about regions
and how to use them are available in 
<xref linkend="sect.Geom.LogVol.SubReg" />. 
As an example, suppose a user defines three regions, corresponding to 
the tracking volume, the calorimeter and the bulk structure of a
detector. For performance reasons, the user may not be interested
in the detailed development of electromagnetic showers in the
insensitive bulk structure, but wishes to maintain the best
possible accuracy in the tracking region. In such a use case,
Geant4 allows the user to set different production thresholds
("cuts") for each geometrical region. This ability, referred to as
"cuts per region", is also a new feature provided by the Geant4 5.1
release. The general concepts of production thresholds were
presented in the <xref linkend="sect.ProThres" />.
</para>

<para>
Please note that this new feature is intended only for users
who

<orderedlist spacing="compact">
  <listitem><para>
    are simulating the most complex geometries, such as an LHC
    detector, and
  </para></listitem>
  <listitem><para>
    are experienced in simulating electromagnetic showers in
    matter.
  </para></listitem>
</orderedlist>
</para>

<para>
We strongly recommend that results generated with this new feature
be compared with results using the same geometry and uniform
production thresholds. Setting completely different cut values for
individual regions may break the coherent and comprehensive
accuracy of the simulation. Therefore cut values should be
carefully optimized, based on a comparison with results obtained
using uniform cuts.
</para>

</sect2>


<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.CutReg.DefReg">
<title>
Default Region
</title>

<para>
The world volume is treated as a region by default. A
<emphasis>G4Region</emphasis> object is automatically assigned to the world
volume and is referred to as the "default region". The production
cuts for this region are the defaults which are defined in the
<emphasis>UserPhysicsList</emphasis>. Unless the user defines different cut
values for other regions, the cuts in the default region will be
used for the entire geometry.
</para>

<para>
Please note that the default region and its default production
cuts are created and set automatically by <emphasis>G4RunManager</emphasis>. 
The user is <emphasis role="bold">not</emphasis> allowed to set a region to 
the world volume, <emphasis role="bold">nor</emphasis> to assign other 
production cuts to the default region.
</para>

</sect2>


<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.CutReg.Assig">
<title>
Assigning Production Cuts to a Region
</title>

<para>
In the <literal>SetCuts()</literal> method of the user's physics list, the
user must first define the default cuts. Then a
<emphasis>G4ProductionCuts</emphasis> object must be created and initialized with
the cut value desired for a given region. This object must in turn
be assigned to the region object, which can be accessed by name
from the <emphasis>G4RegionStore</emphasis>. An example <literal>SetCuts()</literal> 
code follows.

<example id="programlist_CutReg_1">
<title>
<literal>Setting production cuts to a region</literal>
</title>

<programlisting>
void MyPhysicsList::SetCuts()
{
  // default production thresholds for the world volume
  SetCutsWithDefault();

  // Production thresholds for detector regions
  G4Region* region;
  G4String regName;
  G4ProductionCuts* cuts;

  regName = "tracker";
  region = G4RegionStore::GetInstance()-&gt;GetRegion(regName);
  cuts = new G4ProductionCuts;
  cuts-&gt;SetProductionCut(0.01*mm); // same cuts for gamma, e- and e+
  region-&gt;SetProductionCuts(cuts);

  regName = "calorimeter";
  region = G4RegionStore::GetInstance()-&gt;GetRegion(regName);
  cuts = new G4ProductionCuts;
  cuts-&gt;SetProductionCut(0.01*mm,G4ProductionCuts::GetIndex("gamma"));
  cuts-&gt;SetProductionCut(0.1*mm,G4ProductionCuts::GetIndex("e-"));
  cuts-&gt;SetProductionCut(0.1*mm,G4ProductionCuts::GetIndex("e+"));
  region-&gt;SetProductionCuts(cuts);
}
</programlisting>
</example>
</para>


</sect2>
</sect1>