The ProcessManager of a particle has a responsibility to provide a right ordering of process invocations. G4SteppingManager invokes processes in each phase just following the order given by the ProcessManager.

The design of tracking has changed to provide the unified treatment for all of the generalized process, including transportation and parameterization.

Tracking category is almost stable already. No farther big change will not be done.

G4Step keeps transient information in a step. G4Step has two object called PreStepPoint and PostStepPoint. These two are objects of the class G4StepPoint.

G4Step

• Pointers to PreStep and PostStepPoint, step length, deltas between PreStepPoint and PostStepPoint, pointer to G4Track and etc.

G4StepPoint

• (x, y, z, t), (px, py, pz, Ek), Momentum direction and etc

G4Track keeps information of the final status of the particle after the completion of one step.

• G4Track has information of previous step during the 'AlongStepDoIt' invocations.
• Only after finishing all 'AlongStepDoIt', G4Track will have the final information.

G4Track will be updated each time after the invocation of a ‘PostStepDoIt’.

• (x, y, z), time, momentum direction, kinetic energy and etc

G4ParticleChange (although its name) keeps the final state of the particle after a physics process has been invoked. Information in G4ParticleChange are:

• final momentum direction of the parent particle
• final kinetic energy of the parent particle
• final position of the parent particle
• final global time of the parent particle
• final proper time of the parent particle
• and etc.

All of AlongSepDoit’s are always invoked if provided.

AlongStepDoIt’s are invoked in the phase G4SteppingManger is transporting a particle by one step. Each change to the track information is recorded and accumulated in G4Step. However, track information themselves (data members G4Track) are not modified.

After all AlongStepDoIt's are invoked, G4Track data members will be updated by referring to G4Step.