// @(#)root/mathcore:$Id: PxPyPzM4D.h 21503 2007-12-19 17:34:54Z moneta $
// Authors: W. Brown, M. Fischler, L. Moneta    2005  

/**********************************************************************
*                                                                    *
* Copyright (c) 2005 , LCG ROOT MathLib Team                         *
*                                                                    *
*                                                                    *
**********************************************************************/

// Header file for class PxPyPzM4D
// 
// Created by: fischler at Wed Jul 20   2005
//   (starting from PxPyPzM4D by moneta)
// 
// Last update: $Id: PxPyPzM4D.h 21503 2007-12-19 17:34:54Z moneta $
// 
#ifndef ROOT_Math_GenVector_PxPyPzM4D 
#define ROOT_Math_GenVector_PxPyPzM4D  1

#ifndef ROOT_Math_GenVector_eta
#include "Math/GenVector/eta.h"
#endif

#ifndef ROOT_Math_GenVector_GenVector_exception 
#include "Math/GenVector/GenVector_exception.h"
#endif


#include <cmath>

namespace ROOT { 
  
namespace Math { 
    
//__________________________________________________________________________________________
/** 
    Class describing a 4D coordinate system 
    or momentum-energy vectors stored as (Px, Py, Pz, M).
    This system is useful to describe ultra-relativistic particles 
    (like electrons at LHC) to avoid numerical errors evaluating the mass 
    when E >>> m
    The metric used is (-,-,-,+)
    Spacelike particles (M2 < 0) are described with negative mass values, 
    but in this case m2 must alwasy be less than P2 to preserve a positive value of E2
    
    @ingroup GenVector
*/ 

template <class ScalarType = double> 
class PxPyPzM4D { 

public : 

   typedef ScalarType Scalar;

   // --------- Constructors ---------------

   /**
      Default constructor  with x=y=z=m=0 
   */
   PxPyPzM4D() : fX(0), fY(0), fZ(0), fM(0) { }


   /**
      Constructor  from x, y , z , m values
   */
   PxPyPzM4D(Scalar x, Scalar y, Scalar z, Scalar m) : 
      fX(x), fY(y), fZ(z), fM(m) { 
     
      if (fM < 0) RestrictNegMass();
   }

   /**
      construct from any 4D  coordinate system class 
      implementing X(), Y(), X() and M()
   */
   template <class CoordSystem> 
   explicit PxPyPzM4D(const CoordSystem & v) : 
      fX( v.X() ), fY( v.Y() ), fZ( v.Z() ), fM( v.M() )  
   { }

   // for g++  3.2 and 3.4 on 32 bits found that the compiler generated copy ctor and assignment are much slower 
   // so we decided to re-implement them ( there is no no need to have them with g++4)
   /**
      copy constructor
    */
   PxPyPzM4D(const PxPyPzM4D & v) : 
      fX(v.fX), fY(v.fY), fZ(v.fZ), fM(v.fM) { }
      
   /**
      assignment operator 
    */
   PxPyPzM4D & operator = (const PxPyPzM4D & v) { 
      fX = v.fX;  
      fY = v.fY;  
      fZ = v.fZ;  
      fM = v.fM;
      return *this;
   }


   /**
      Set internal data based on an array of 4 Scalar numbers
   */ 
   void SetCoordinates( const Scalar src[] ) { 
      fX=src[0]; fY=src[1]; fZ=src[2]; fM=src[3]; 
      if (fM < 0) RestrictNegMass();
   }

   /**
      get internal data into an array of 4 Scalar numbers
   */ 
   void GetCoordinates( Scalar dest[] ) const 
   { dest[0] = fX; dest[1] = fY; dest[2] = fZ; dest[3] = fM; }

   /**
      Set internal data based on 4 Scalar numbers
   */ 
   void SetCoordinates(Scalar  x, Scalar  y, Scalar  z, Scalar m) { 
      fX=x; fY=y; fZ=z; fM=m;
      if (fM < 0) RestrictNegMass();
   }

   /**
      get internal data into 4 Scalar numbers
   */ 
   void GetCoordinates(Scalar& x, Scalar& y, Scalar& z, Scalar& m) const 
   { x=fX; y=fY; z=fZ; m=fM;}  				

   // --------- Coordinates and Coordinate-like Scalar properties -------------

   // cartesian (Minkowski)coordinate accessors 

   Scalar Px() const { return fX;}
   Scalar Py() const { return fY;}
   Scalar Pz() const { return fZ;}
   Scalar M() const  { return fM; }

   Scalar X() const { return fX;}
   Scalar Y() const { return fY;}
   Scalar Z() const { return fZ;}

   // other coordinate representation
   /**
      Energy 
   */ 				  
   Scalar E()  const { return std::sqrt(E2() ); }

   Scalar T() const { return E();}

   /**
      squared magnitude of spatial components
   */
   Scalar P2() const { return fX*fX + fY*fY + fZ*fZ; } 

   /**
      magnitude of spatial components (magnitude of 3-momentum)
   */
   Scalar P() const { return std::sqrt(P2()); } 
   Scalar R() const { return P(); } 

   /**
      vector magnitude squared (or mass squared)
      In case of negative mass (spacelike particles return negative values)
   */
   Scalar M2() const   { 
      return ( fM  >= 0 ) ?  fM*fM :  -fM*fM; 
   }
   Scalar Mag2() const { return M2(); } 

   Scalar Mag() const    { return M(); }

   /**
      energy squared
   */
   Scalar E2() const { 
      Scalar e2 =  P2() + M2(); 
      // protect against numerical errors when M2() is negative
      return e2 > 0 ? e2 : 0; 
   }

   /** 
       transverse spatial component squared  
   */
   Scalar Pt2()   const { return fX*fX + fY*fY;}
   Scalar Perp2() const { return Pt2();}

   /**
      Transverse spatial component (P_perp or rho)
   */
   Scalar Pt()   const { return std::sqrt(Perp2());}
   Scalar Perp() const { return Pt();}
   Scalar Rho()  const { return Pt();}

   /** 
       transverse mass squared
   */
   Scalar Mt2() const { return E2() - fZ*fZ; } 

   /**
      transverse mass
   */
   Scalar Mt() const { 
      Scalar mm = Mt2();
      if (mm >= 0) {
         return std::sqrt(mm);
      } else {
         GenVector_exception e ("PxPyPzM4D::Mt() - Tachyonic:\n"
                                "    Pz^2 > E^2 so the transverse mass would be imaginary");
         Throw(e);  
         return -std::sqrt(-mm);
      }
   } 

   /** 
       transverse energy squared
   */
   Scalar Et2() const {  // is (E^2 * pt ^2) / p^2 
      // but it is faster to form p^2 from pt^2
      Scalar pt2 = Pt2();
      return pt2 == 0 ? 0 : E2() * pt2/( pt2 + fZ*fZ );
   }

   /**
      transverse energy
   */
   Scalar Et() const { 
      Scalar etet = Et2();
      return std::sqrt(etet);
   }

   /**
      azimuthal angle 
   */
   Scalar Phi() const  { 
      return (fX == 0.0 && fY == 0.0) ? 0.0 : std::atan2(fY,fX);
   }

   /**
      polar angle
   */
   Scalar Theta() const {
      return (fX == 0.0 && fY == 0.0 && fZ == 0.0) ? 0.0 : std::atan2(Pt(),fZ);
   }

   /** 
       pseudorapidity
   */
   Scalar Eta() const {
      return Impl::Eta_FromRhoZ ( Pt(), fZ); 
   }

   // --------- Set Coordinates of this system  ---------------


   /**
      set X value 
   */
   void SetPx( Scalar  x) { 
      fX = x; 
   }
   /**
      set Y value 
   */
   void SetPy( Scalar  y) { 
      fY = y; 
   }
   /**
      set Z value 
   */
   void SetPz( Scalar  z) { 
      fZ = z; 
   }
   /**
      set T value 
   */
   void SetM( Scalar  m) { 
      fM = m; 
      if (fM < 0) RestrictNegMass();
   }

   /** 
       set all values  
   */
   void SetPxPyPzE(Scalar px, Scalar py, Scalar pz, Scalar e);

   // ------ Manipulations -------------
  
   /**
      negate the 4-vector
   */
   void Negate( ) { fX = -fX; fY = -fY;  fZ = -fZ; fM = -fM;}

   /**
      scale coordinate values by a scalar quantity a
   */
   void Scale( const Scalar & a) { 
      fX *= a; 
      fY *= a; 
      fZ *= a; 
      fM *= a; 
   }
 
   /**
      Assignment from a generic coordinate system implementing 
      x(), y(), z() and t()
   */
   template <class AnyCoordSystem> 
   PxPyPzM4D & operator = (const AnyCoordSystem & v) { 
      fX = v.x();  
      fY = v.y();  
      fZ = v.z();  
      fM = std::sqrt ( v.t()*v.t() - P2() );
      return *this;
   }

   /**
      Exact equality
   */  
   bool operator == (const PxPyPzM4D & rhs) const {
      return fX == rhs.fX && fY == rhs.fY && fZ == rhs.fZ && fM == rhs.fM;
   }
   bool operator != (const PxPyPzM4D & rhs) const {return !(operator==(rhs));}


   // ============= Compatibility section ==================

   // The following make this coordinate system look enough like a CLHEP
   // vector that an assignment member template can work with either
   Scalar x() const { return X(); }
   Scalar y() const { return Y(); }
   Scalar z() const { return Z(); } 
   Scalar t() const { return E(); } 



#if defined(__MAKECINT__) || defined(G__DICTIONARY) 

   // ====== Set member functions for coordinates in other systems =======

   void SetPt(Scalar pt);   

   void SetEta(Scalar eta);  

   void SetPhi(Scalar phi);  

   void SetE(Scalar t); 

#endif

private:

   // restrict the value of negative mass to avoid unphysical negative E2 values 
   // M2 must be less than P2 for the tachionic particles - otherwise use positive values
   inline void RestrictNegMass() {
      if ( fM >=0 ) return;
      if ( P2() - fM*fM  < 0 ) { 
         GenVector_exception e("PxPyPzM4D::unphysical value of mass, set to closest physical value");
         Throw(e);
         fM = - P();
      }
      return;
   } 


   /**
      (contigous) data containing the coordinate values x,y,z,t
   */

   ScalarType fX;
   ScalarType fY;
   ScalarType fZ;
   ScalarType fM;

}; 
    
} // end namespace Math  
} // end namespace ROOT


// move implementations here to avoid circle dependencies

#include "Math/GenVector/PxPyPzE4D.h"
#include "Math/GenVector/PtEtaPhiM4D.h"

namespace ROOT { 

namespace Math { 

template <class ScalarType>  
inline void PxPyPzM4D<ScalarType>::SetPxPyPzE(Scalar px, Scalar py, Scalar pz, Scalar e) {  
   *this = PxPyPzE4D<Scalar> (px, py, pz, e);
}


#if defined(__MAKECINT__) || defined(G__DICTIONARY) 
     
  // ====== Set member functions for coordinates in other systems =======

  // ====== Set member functions for coordinates in other systems =======
 
template <class ScalarType>  
inline void PxPyPzM4D<ScalarType>::SetPt(ScalarType pt) {  
   GenVector_exception e("PxPyPzM4D::SetPt() is not supposed to be called");
   Throw(e);
   PtEtaPhiE4D<ScalarType> v(*this); v.SetPt(pt); *this = PxPyPzM4D<ScalarType>(v);
}
template <class ScalarType>  
inline void PxPyPzM4D<ScalarType>::SetEta(ScalarType eta) {  
   GenVector_exception e("PxPyPzM4D::SetEta() is not supposed to be called");
   Throw(e);
   PtEtaPhiE4D<ScalarType> v(*this); v.SetEta(eta); *this = PxPyPzM4D<ScalarType>(v);
}
template <class ScalarType>  
inline void PxPyPzM4D<ScalarType>::SetPhi(ScalarType phi) {  
   GenVector_exception e("PxPyPzM4D::SetPhi() is not supposed to be called");
   Throw(e);
   PtEtaPhiE4D<ScalarType> v(*this); v.SetPhi(phi); *this = PxPyPzM4D<ScalarType>(v);
}
template <class ScalarType>  
inline void PxPyPzM4D<ScalarType>::SetE(ScalarType t) {  
   GenVector_exception e("PxPyPzM4D::SetM() is not supposed to be called");
   Throw(e);
   PxPyPzE4D<ScalarType> v(*this); v.SetE(t); 
   *this = PxPyPzM4D<ScalarType>(v);
}


#endif  // endif __MAKE__CINT || G__DICTIONARY

} // end namespace Math

} // end namespace ROOT



#endif // ROOT_Math_GenVector_PxPyPzM4D