How can I use my own particle correction class ?

When using your own classes they should be put in a directory which is linked to via the enviroment variable $CHANSER_CLASSES . Make sure this variable is set before using the skeleton class maker.

Use chanser_skeleton to make template class code, this code will inherit from BaseCut,

  chanser_skeleton CreateClassParticleCorrection.C name=MyParticleCorrection

(Please choose something more meaningful than MyParticleCorrection, this is just for example.)

The class .h and .cpp files should now be in $CHANSER_CLASSES

  ls $CHANSER_CLASSES
  LoadMyClasses.C  MyParticleCorrection.cpp  MyParticleCorrection.h

The file LoadMyClasses.C is generated automatically the first time you make a class. And is used to compile and load your class at run time with the line,

  Loader::Compile("$CHANSER_CLASSES/MyParticleCorrection.cpp");

You can now edit MyParticleCorrection.h to define your own correction. The principle is you can access a clas12root region_particle in the ParticleCorrect function and you can access any of the DST data for that particle from this and so base your correction on any amount of particle detector information. Most useful is probably getRegion as corrections are likely to be different for FT, FD and CD. Here I will just multiply the particle momentum by a constant factor,

    void ParticleCorrect(chanser::BaseParticle* part) const noexcept override{
      auto c12p = static_cast<const chanser::CLAS12Particle*>(part);
      auto c12=p->CLAS12(); //if you require other DST data
      if(c12->getRegion()!=clas12::FD) return; //e.g only FD correction
  
      Double_t p_mag = part->P4p()->P();
      p_mag*=_a0;  //apply correction...
      part->SetP(p_mag_corrected);
    }

Note if I include auto c12=p->CLAS12(); then I can use c12 to access DST data, e.g. c12->cal(PCAL)->getEnergy();

You can add as many parameters as you want through the constructor, adding each as a data member of the class

i.e. I add the contructor looks like

  MyParticleCorrection(Float_t a0)_a0{a0}{}

And include the data member

  Float_t _a0{0};

You should also edit the print statement to give a meaningful summary of your correction so the final state class can give a full report of its algorithms

   void Print(Option_t* option = "")const final{
     std::cout<<"\t\t"<<ClassName()<<" with parameter ";
     std::cout<<_a0<<std::endl;
   }

To use it with a ParticleCorrectionManager I register it pretopo so it is already applied before the topology function,

  ParticleCorrectionManager pcorrm{"IMadeThisCorrection"};
  pcorrm.AddParticle("e-",new MyParticleCorrection(1.1)); //use it on electrons
  pcorrm.AddParticle("pi+",new MyParticleCorrection(0.9)); //use it pi+
  FS->RegisterPreTopoAction(pcorrm); //PRETOPO