Changeset 1222 for trunk/documents/UserDoc/DocBookUsersGuides/ForApplicationDeveloper/xml/Detector/electroMagneticField.xml

Timestamp:

Dec 16, 2009, 12:14:47 PM (15 years ago)

Author:

garnier

Message:

CVS update

File:

• trunk/documents/UserDoc/DocBookUsersGuides/ForApplicationDeveloper/xml/Detector/electroMagneticField.xml (modified) (3 diffs)

trunk/documents/UserDoc/DocBookUsersGuides/ForApplicationDeveloper/xml/Detector/electroMagneticField.xml

@@ -13 +13 @@
 <!--    Corrections, changes by: John APOSTOLAKIS, 7-Jul-2005 -->
 <!--    Converted to DocBook: Katsuya Amako, Aug-2006         -->
+<!--    Corrections, changes by: John APOSTOLAKIS,15-Dec-2009 -->
 <!--                                                          -->
 <!-- ******************************************************** -->
@@ -441 +442 @@
 
 <para>
+A new stepper for propagation in magnetic field is available in 
+release 9.3.  Choosing the G4NystromRK4 stepper provides accuracy 
+near that of G4ClassicalRK4 (4th order) with a significantly reduced 
+cost in field evaluation.   Using a novel analytical expression for 
+estimating the error of a proposed step and the Nystrom reuse of the 
+mid-point field value, it requires only 2 additional field 
+evaluations per attempted step, in place of 10 field evaluations of 
+ClassicalRK4 (which uses the general midpoint method for estimating 
+the step error.) 
+
+<informalexample>
+<programlisting>
+   G4Mag_UsualEqRhs* 
+      pMagFldEquation = new G4Mag_UsualEqRhs(fMagneticField); 
+   fStepper = new G4NystromRK4( pMagFldEquation ); 
+</programlisting>
+</informalexample>
+</para>
+
+<para>
+It is proposed as an alternative stepper in the case of a pure 
+magnetic field.  It is not applicable for the simulation of electric 
+or full electromagnetic or other types of field.  For a pure 
+magnetic field, results should be fully compatible with the results 
+of ClassicalRK4 in nearly all cases.  ( The only potential exceptions 
+are large steps for tracks with small momenta - which cannot be 
+integrated well by any RK method except the Helical extended methods.)
+</para>
+
+<para>
 You can choose an alternative stepper either when the field
 manager is constructed or later. At the construction of the
@@ -546 +577 @@
 the position of the track after a number of boundary crossings is
 directly proportional to the number of boundaries.
+</para>
+
+</sect3>
+
+
+<!-- ******************* Section (Level#3) ****************** -->
+<sect3 id="sect.EMField.Pract.RedNumCall">
+<title>
+Reducing the number of field calls to speed-up simulation
+</title>
+
+<para>
+An additional method to reduce the number of field evaluations is 
+to utilise the new class G4CachedMagneticField class.  It is 
+applicable only for pure magnetic fields which do not vary with time. 
+
+
+<informalexample>
+<programlisting>
+  G4MagneticField * pMagField;  // Your field - Defined elsewhere
+
+  G4double                 distanceConst = 2.5 * millimeter; 
+  G4MagneticField * pCachedMagField= new G4CachedMagneticField(  pMagField,  distanceConst); 
+</programlisting>
+</informalexample>
 </para>