Mask/include/Vec4.h

/*
	Class which represents a 4-momentum vector. Can perform vector addition, subtraction, dot product
	and generate a boost vector to its rest frame as well as apply a boost to itself.

	--GWM Dec 2020.
*/
#ifndef VEC4_H
#define VEC4_H

#include <cmath>

namespace Mask {

	class Vec4 {
	public:
		Vec4();
		Vec4(double px, double py, double pz, double E);
		virtual ~Vec4();
		void SetVectorCartesian(double px, double py, double pz, double E);
		void SetVectorSpherical(double theta, double phi, double p, double E);
	
		inline double GetE() const { return m_data[3]; }
		inline double GetPx() const { return m_data[0]; }
		inline double GetPy() const { return m_data[1]; }
		inline double GetPz() const { return m_data[2]; }
		inline double GetP() const { return std::sqrt(m_data[0]*m_data[0] + m_data[1]*m_data[1] + m_data[2]*m_data[2]); }
		inline double GetPxy() const { return std::sqrt(m_data[0]*m_data[0] + m_data[1]*m_data[1]); }
		inline double GetTheta() const { return GetPxy() == 0.0 && GetPz() == 0.0 ? 0.0 : Atan2(GetPxy(), GetPz()); }
		inline double GetPhi() const {
			double phi = Atan2(GetPy(), GetPx());
			if(phi<0) phi += 2.0*M_PI;
			return GetPx() == 0.0 && GetPy() == 0.0 ? 0.0 : phi;
		}
	
		inline double GetInvMass() const { return std::sqrt(GetE()*GetE() - GetP()*GetP()); }
		inline double GetKE() const { return GetE() - GetInvMass(); }
		inline const double* GetBoost() const { return &m_boost[0]; }
	
		void ApplyBoost(const double* boost);
	
		//Only intended for use in looping access!
		inline const double operator[] (int index) const { return index>3 || index < 0 ? 0.0 : m_data[index]; }
	
		inline Vec4& operator=(const Vec4& rhs) { SetVectorCartesian(rhs.GetPx(), rhs.GetPy(), rhs.GetPz(), rhs.GetE()); return *this; }
		inline Vec4 operator+(const Vec4& rhs) const { return Vec4(rhs.GetPx()+GetPx(), rhs.GetPy()+GetPy(), rhs.GetPz()+GetPz(), rhs.GetE()+GetE()); }
		inline Vec4 operator-(const Vec4& rhs) const { return Vec4(rhs.GetPx()-GetPx(), rhs.GetPy()-GetPy(), rhs.GetPz()-GetPz(), rhs.GetE()-GetE()); }
		
		double Dot(const Vec4& rhs) const;
		Vec4 Cross(const Vec4& rhs) const;
	
	private:
		void CalcBoostToCM();
	
		//use instead of std::atan2. Better controll over x=0
		inline double Atan2(double y, double x) const { 
			if(x != 0) return std::atan2(y, x);
			else if( y > 0 ) return M_PI/2.0;
			else if( y < 0 ) return -M_PI/2.0;
			else return 0.0;
		}
	
		double m_data[4];
		double m_boost[3];
	
	};

}

#endif