CLHEP Components

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)

• 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

millimetermm1 meter m 1000mm . m3
mmm ..
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 90.3GeV,
density 11mg/cm3
G4double radius10.m // internally
converted radius10000 . G4double xposition
(radiuscos(alpharad))cm // is this really what
you want to do?? G4double yposition
(radiussin(alpharad))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 ltlt KineticEnergy/KeV ltlt KeV ltltendl
cout ltlt G4BestUnit(StepSize, Length) ltltendl
G4UnitDefinitionPrintUnitsTable
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 2.54cm
G4UnitDefinition (inch,in,Length,25.4mm)
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 pnew G4ThreeVector(10,20,100)
• Every component can be accessed very easily
• G4double pxp-gtx()
• and set very easily
• p-gtsetZ(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-gtunit()
• rotated around one of the cartesian axes
• p-gtrotateY(2.73)
• or around any other 3-vector
• p-gtrotate(1.57,G4ThreeVector(10,20,30))
• for reference
• CLHEP_BASE_DIR/include/CLHEP/Vector/ThreeVector.h
  
• wwwinfo.cern.ch/asd/lhc/clhep/manual/RefGuide/Ve
  ctor/Hep3Vector.html

10
Rotation Matrices

• Geant4 uses the rotation matrix implementation
  which comes with CLHEP (HepRotation, typedefd
  into G4RotationMatrix)
• include G4RotationMatrix.hh
• .
• G4RotationMatrix rm new G4RotationMatrix
• You can then rotate about the coordinate axes
• rm-gtrotateX(45deg) // rotation about X
• and combine several rotations into a 3D one
• rm-gtrotateX(30deg)
• rm-gtrotateY(20deg)

11
Rotation Matrices (2)

• You can rotate about a specified vector
• rm-gtrotate(45deg,Hep3Vector(1.,1.,.3))
• or specify the direction of the three cartesian
  axes after the rotation
• rm-gtrotateAxes( 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-gtinvert()

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-gtgetAngleAxis(angle,axis)
• to reset a rotation matrix use the default
  constructor
• rmG4RotationMatrix()
• documentation at
• CLHEP_BASE_DIR/include/CLHEP/Vector/Rotation.h
• wwwinfo.cern.ch/asd/lhc/clhep/manual/RefGuide/Ve
  ctor/HepRotation.html