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ElzKin.h

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#ifndef ATLFAST_ELZKIN_H
#define ATLFAST_ELZKIN_H
#include <math.h>


namespace Atlfast {

  float ElzRapidity(float pt, float pz){
    float etalog = log((sqrt(pt*pt + pz*pz) + sqrt(pz*pz))/pt);
    if (pz < 0 ) return -sqrt(etalog*etalog);
    else         return  sqrt(etalog*etalog);
  }
  float ElzPhi(float x, float y){
//   Compute phi angle of particle
// ... this is a copy of function ULANGL
//  .. sign(a,b) = -abs(a) if b <  0
//               =  abs(a) if b >= 0
    float angle = 0;
    const float kPI  = 4*atan(1.0);
    float r = sqrt(x*x + y*y);
    if (r < 1e-20) return angle;
    if (sqrt(x*x)/r < 0.8) {
      //      angle = Sign((float)sqrt(acos(x/r)*acos(x/r)), y);
      angle = (float)sqrt(acos(x/r)*acos(x/r));
      angle = (y>0)? abs(angle):-abs(angle);
    } else {
      angle = asin(y/r);
      if (x < 0 ) {
        if(angle >= 0) angle =  kPI - angle;
        else           angle = -kPI - angle;
      }
    }
    return angle;
  }
}
#endif

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