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CLHEP Components

CLHEP Components. Geant4 and CLHEP. Geant4 makes a rather substantial use of CLHEP components System of units Vector classes and matrices G4ThreeVector (typedef to Hep3Vector) G4RotationMatrix (typedef to HepRotation) G4LorentzVector (typedef to HepLorentzVector)

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CLHEP Components

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  1. CLHEP Components

  2. Geant4 and CLHEP • Geant4 makes a rather substantial use of CLHEP components • System of units • Vector classes and matrices • G4ThreeVector (typedef to Hep3Vector) • G4RotationMatrix (typedef to HepRotation) • G4LorentzVector (typedef to HepLorentzVector) • G4LorentzRotation (typedef to HepLorentzRotation) • Geometrical classes • G4Plane3D (typedef to HepPlane3D) • G4Transform3D (typedef to HepTransform3D) • G4Normal3D (typedef to HepNormal3D) • G4Point3D (typedef to HepPoint3D) • G4Vector3D (typedef to HepVector3D)

  3. System of units • Geant4 offers the possibility to choose and use the units one prefers for any quantity • Geant4 uses an internal and consistent set of units based on: • millimeter (mm) • nanosecond (ns) • Mega electron Volt (MeV) • Positron charge (eplus) • Degree Kelvin (kelvin) • Amount of substance (mole) • Luminosity intensity (candela) • Radian (radian) • steradian (steradian)

  4. System of units (2) millimeter=mm=1; meter = m = 1000*mm; ……. m3 = m*m*m; …….. • All the units are defined from the basic ones • These definitions are available in the file • source/global/management/include/SystemOfUnits • … and are now part of CLHEP • The user is free to change the system of units to be used by the kernel

  5. System of units (3) • Avoid hard coded data • you better specify the unit of the data you are going to introduce • The Geant4 code is written respecting these specification and this makes the code independent from the system of units chosen by the user • Be careful!!! • Some built-in commands for the User interface require the unit to be specified G4double Size = 15.*km, KineticEnergy = 90.3*GeV, density = 11*mg/cm3; G4double radius=10.*m; // internally converted: radius=10000 …. G4double xposition = (radius*cos(alpha*rad))*cm // is this really what you want to do?? G4double yposition = (radius*sin(alpha*rad))*cm /gun/energy 10 GeV

  6. System of units (4) • To output the data on the unit you wish you must DIVIDE the data by the corresponding unit • You can let Geant4 decide which is the most appropriate unit to represent your data. It is just sufficient to specify which category (length, time, energy…) does it belong to: • You can print the whole table of units by using the static function cout << KineticEnergy/KeV << “ KeV “<<endl; cout << G4BestUnit(StepSize, “Length”) <<endl G4UnitDefinition::PrintUnitsTable

  7. System of units (5) • You may introduce new units if you wish: • by completing the file SystemOfUnits.hh • by using the class G4UnitDefinition and creating a new object of it • G4UnitDefinition (name, symbol, category, value) #include “SystemOfUnits.hh” static const G4double inch = 2.54*cm; G4UnitDefinition (“inch”,”in”,”Length”,25.4*mm);

  8. 3-Vectors • Geant4 makes use of the CLHEP HepVector3D and Hep3Vector for implementing several 3-dimensional object (G4ThreeVector, G4ParticleMomentum…) • The definition of a 3-vector is pretty straightforward: G4ThreeVector *p=new G4ThreeVector(10,20,100); • Every component can be accessed very easily: G4double px=p->x(); • and set very easily; p->setZ(50); • the components in polar coordinates are give by phi(), theta(), mag() • and set using: setPhi(), setTheta(), setMag()

  9. 3-Vectors (2) • They can be normalized: p->unit(); • rotated around one of the cartesian axes p->rotateY(2.73); • or around any other 3-vector p->rotate(1.57,G4ThreeVector(10,20,30)); • for reference: $CLHEP_BASE_DIR/include/CLHEP/Vector/ThreeVector.h wwwinfo.cern.ch/asd/lhc++/clhep/manual/RefGuide/Vector/Hep3Vector.html

  10. Rotation Matrices • Geant4 uses the rotation matrix implementation which comes with CLHEP (HepRotation, typedef’d into G4RotationMatrix) #include “G4RotationMatrix.hh” …. G4RotationMatrix *rm = new G4RotationMatrix; • You can then rotate about the coordinate axes: rm->rotateX(45*deg); // rotation about X • and combine several rotations into a 3D one: rm->rotateX(30*deg); rm->rotateY(20*deg);

  11. Rotation Matrices (2) • You can rotate about a specified vector rm->rotate(45*deg,Hep3Vector(1.,1.,.3)); • or specify the direction of the three cartesian axes after the rotation rm->rotateAxes( Hep3Vector(-sin(a),0,cos(a)), Hep3Vector(cos(a),0,sin(a)), Hep3Vector(0,1,0)); • a rotation matrix can be inverted by using the invert method rm->invert();

  12. Rotation Matrices (3) • The angles made by the rotated axes against the original axes can be obtained with the set of functions: • phiX(),phiY(),phiZ(),thetaX(),thetaY(),thetaZ() • …or one can get the rotation angle and the rotation axis (awkward) G4double angle; G4ThreeVector axis; rm->getAngleAxis(angle,axis); • to reset a rotation matrix use the default constructor *rm=G4RotationMatrix(); • documentation at: $CLHEP_BASE_DIR/include/CLHEP/Vector/Rotation.h wwwinfo.cern.ch/asd/lhc++/clhep/manual/RefGuide/Vector/HepRotation.html

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