source: trunk/documents/UserDoc/DocBookUsersGuides/ForApplicationDeveloper/xml/TrackingAndPhysics/userLimits.xml

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<!--  [History]                                               -->
<!--    Created by: Makoto Asai,          30-Mar-2006         -->
<!--    Converted to DocBook: Katsuya Amako, Aug-2006         -->
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<!-- ******************* Section (Level#1) ****************** -->
<sect1 id="sect.Ulim">
<title>
User Limits
</title>


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

<para>
The user can define artificial limits affecting to the Geant4
tracking.

<informalexample>
<programlisting>
G4UserLimits(G4double uStepMax = DBL_MAX,
             G4double uTrakMax = DBL_MAX,
             G4double uTimeMax = DBL_MAX,
             G4double uEkinMin = 0.,
             G4double uRangMin = 0. );
</programlisting>
</informalexample>

<informaltable>
<tgroup cols="2">
  <tbody>
  <row>
    <entry>
      <literal>uStepMax</literal>
    </entry>
    <entry>
      Maximum step length
    </entry>
  </row>
  <row>
    <entry>
      <literal>uTrakMax</literal>
    </entry>
    <entry>
      Maximum total track length
    </entry>
  </row>
  <row>
    <entry>
      <literal>uTimeMax</literal>
    </entry>
    <entry>
      Maximum global time for a track
    </entry>
  </row>
  <row>
    <entry>
      <literal>uEkinMin</literal>
    </entry>
    <entry>
      Minimum remaining kinetic energy for a track
    </entry>
  </row>
  <row>
    <entry>
      <literal>uRangMin</literal>
    </entry>
    <entry>
      Minimum remaining range for a track
    </entry>
  </row>
  </tbody>
</tgroup>
</informaltable>

Note that <literal>uStepMax</literal> is affecting to each step, while all
other limits are affecting to a track.
</para>

<para>
The user can set <literal>G4UserLimits</literal> to logical volume and/or
to a region. User limits assigned to logical volume do not
propagate to daughter volumes, while User limits assigned to region
propagate to daughter volumes unless daughters belong to another
region. If both logical volume and associated region have user
limits, those of logical volume win.
</para>

</sect2>


<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.Ulim.Proc">
<title>
Processes co-working with G4UserLimits
</title>

<para>
In addition to instantiating <literal>G4UserLimits</literal> and setting it
to logical volume or region, the user has to assign the following
process(es) to particle types he/she wants to affect. If none of
these processes is assigned, that kind of particle is not affected
by <literal>G4UserLimits</literal>.

<variablelist>
  <varlistentry>
    <term>
      Limitation to step (<literal>uStepMax</literal>)
    </term>
    <listitem><para>
      <literal>G4StepLimiter</literal> process must be defined to affected
      particle types. This process limits a step, but it does not kill a
      track.
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term>
      Limitations to track (<literal>uTrakMax, uTimeMax, uEkinMin,
      uRangMin</literal>)
    </term>
    <listitem><para>
      <literal>G4UserSpecialCuts</literal> process must be defined to affected
      particle types. This process limits a step and kills the track when
      the track comes to one of these limits. Step limitation occurs only
      for the final step.
    </para></listitem>
  </varlistentry>
</variablelist>
</para>

<para>
Example of <literal>G4UserLimits</literal> can be found in
examples/novice/N02 : see <literal>DetectorConstruction</literal> and
<literal>PhysicsList</literal>.
</para>


</sect2>
</sect1>