KFParticleBase.cxx

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//---------------------------------------------------------------------------------
// Implementation of the KFParticleBase class
// .
// @author  S.Gorbunov, I.Kisel, I.Kulakov, M.Zyzak
// @version 1.0
// @since   13.05.07
// 
// Class to reconstruct and store the decayed particle parameters.
// The method is described in CBM-SOFT note 2007-003, 
// ``Reconstruction of decayed particles based on the Kalman filter'', 
// http://www.gsi.de/documents/DOC-2007-May-14-1.pdf
//
// This class describes general mathematics which is used by KFParticle class
// 
//  -= Copyright &copy ALICE HLT and CBM L1 Groups =-
//_________________________________________________________________________________


#include "KFParticleBase.h"
#include <cmath>

#include <iostream>

KFParticleBase::KFParticleBase() :fQ(0), fNDF(-3), fChi2(0), fSFromDecay(0), fAtProductionVertex(0), fIsLinearized(0),
  fConstructMethod(2), SumDaughterMass(0), fMassHypo(-1), fId(-1), fDaughtersIds(), fPDG(0)
{ 
  //* Constructor 

  Initialize();
}

void KFParticleBase::Initialize( const Double_t Param[], const Double_t Cov[], Int_t Charge, Double_t Mass )
{
  // Constructor from "cartesian" track, particle mass hypothesis should be provided
  //
  // Param[6] = { X, Y, Z, Px, Py, Pz } - position and momentum
  // Cov [21] = lower-triangular part of the covariance matrix:
  //
  //                (  0  .  .  .  .  . )
  //                (  1  2  .  .  .  . )
  //  Cov. matrix = (  3  4  5  .  .  . ) - numbering of covariance elements in Cov[]
  //                (  6  7  8  9  .  . )
  //                ( 10 11 12 13 14  . )
  //                ( 15 16 17 18 19 20 )


  for( Int_t i=0; i<6 ; i++ ) fP[i] = Param[i];
  for( Int_t i=0; i<21; i++ ) fC[i] = Cov[i];

  Double_t energy = sqrt( Mass*Mass + fP[3]*fP[3] + fP[4]*fP[4] + fP[5]*fP[5]);
  fP[6] = energy;
  fP[7] = 0;
  fQ = Charge;
  fNDF = 0;
  fChi2 = 0;
  fAtProductionVertex = 0;
  fIsLinearized = 0;
  fSFromDecay = 0;

  Double_t energyInv = 1./energy;
  Double_t 
    h0 = fP[3]*energyInv,
    h1 = fP[4]*energyInv,
    h2 = fP[5]*energyInv;

  fC[21] = h0*fC[ 6] + h1*fC[10] + h2*fC[15];
  fC[22] = h0*fC[ 7] + h1*fC[11] + h2*fC[16];
  fC[23] = h0*fC[ 8] + h1*fC[12] + h2*fC[17];
  fC[24] = h0*fC[ 9] + h1*fC[13] + h2*fC[18];
  fC[25] = h0*fC[13] + h1*fC[14] + h2*fC[19];
  fC[26] = h0*fC[18] + h1*fC[19] + h2*fC[20];
  fC[27] = ( h0*h0*fC[ 9] + h1*h1*fC[14] + h2*h2*fC[20] 
             + 2*(h0*h1*fC[13] + h0*h2*fC[18] + h1*h2*fC[19] ) );
  for( Int_t i=28; i<36; i++ ) fC[i] = 0;
  fC[35] = 1.;

  SumDaughterMass = Mass;
  fMassHypo = Mass;
}

void KFParticleBase::Initialize()
{
  //* Initialise covariance matrix and set current parameters to 0.0 

  for( Int_t i=0; i<8; i++) fP[i] = 0;
  for(Int_t i=0;i<36;++i) fC[i]=0.;
  fC[0] = fC[2] = fC[5] = 100.;
  fC[35] = 1.;
  fNDF  = -3;
  fChi2 =  0.;
  fQ = 0;
  fSFromDecay = 0;
  fAtProductionVertex = 0;
  fVtxGuess[0]=fVtxGuess[1]=fVtxGuess[2]=0.;
  fIsLinearized = 0;
  SumDaughterMass = 0;
  fMassHypo = -1;
}

void KFParticleBase::SetVtxGuess( Double_t x, Double_t y, Double_t z )
{
  //* Set decay vertex parameters for linearisation 

  fVtxGuess[0] = x;
  fVtxGuess[1] = y;
  fVtxGuess[2] = z;
  fIsLinearized = 1;
}

Int_t KFParticleBase::GetMomentum( Double_t &p, Double_t &error )  const 
{
  //* Calculate particle momentum

  Double_t x = fP[3];
  Double_t y = fP[4];
  Double_t z = fP[5];
  Double_t x2 = x*x;
  Double_t y2 = y*y;
  Double_t z2 = z*z;
  Double_t p2 = x2+y2+z2;
  p = sqrt(p2);
  error = (x2*fC[9]+y2*fC[14]+z2*fC[20] + 2*(x*y*fC[13]+x*z*fC[18]+y*z*fC[19]) );
  if( error>1.e-16 && p>1.e-4 ){
    error = sqrt(error)/p;
    return 0;
  }
  error = 1.e8;
  return 1;
}

Int_t KFParticleBase::GetPt( Double_t &pt, Double_t &error )  const 
{
  //* Calculate particle transverse momentum

  Double_t px = fP[3];
  Double_t py = fP[4];
  Double_t px2 = px*px;
  Double_t py2 = py*py;
  Double_t pt2 = px2+py2;
  pt = sqrt(pt2);
  error = (px2*fC[9] + py2*fC[14] + 2*px*py*fC[13] );
  if( error>0 && pt>1.e-4 ){
    error = sqrt(error)/pt;
    return 0;
  }
  error = 1.e10;
  return 1;
}

Int_t KFParticleBase::GetEta( Double_t &eta, Double_t &error )  const 
{
  //* Calculate particle pseudorapidity

  Double_t px = fP[3];
  Double_t py = fP[4];
  Double_t pz = fP[5];
  Double_t pt2 = px*px + py*py;
  Double_t p2 = pt2 + pz*pz;
  Double_t p = sqrt(p2);
  Double_t a = p + pz;
  Double_t b = p - pz;
  eta = 1.e10;
  if( b > 1.e-8 ){
    Double_t c = a/b;
    if( c>1.e-8 ) eta = 0.5*log(c);
  }
  Double_t h3 = -px*pz;
  Double_t h4 = -py*pz;  
  Double_t pt4 = pt2*pt2;
  Double_t p2pt4 = p2*pt4;
  error = (h3*h3*fC[9] + h4*h4*fC[14] + pt4*fC[20] + 2*( h3*(h4*fC[13] + fC[18]*pt2) + pt2*h4*fC[19] ) );

  if( error>0 && p2pt4>1.e-10 ){
    error = sqrt(error/p2pt4);
    return 0;
  }

  error = 1.e10;
  return 1;
}

Int_t KFParticleBase::GetPhi( Double_t &phi, Double_t &error )  const 
{
  //* Calculate particle polar angle

  Double_t px = fP[3];
  Double_t py = fP[4];
  Double_t px2 = px*px;
  Double_t py2 = py*py;
  Double_t pt2 = px2 + py2;
  phi = atan2(py,px);
  error = (py2*fC[9] + px2*fC[14] - 2*px*py*fC[13] );
  if( error>0 && pt2>1.e-4 ){
    error = sqrt(error)/pt2;
    return 0;
  }
  error = 1.e10;
  return 1;
}

Int_t KFParticleBase::GetR( Double_t &r, Double_t &error )  const 
{
  //* Calculate distance to the origin

  Double_t x = fP[0];
  Double_t y = fP[1];
  Double_t x2 = x*x;
  Double_t y2 = y*y;
  r = sqrt(x2 + y2);
  error = (x2*fC[0] + y2*fC[2] - 2*x*y*fC[1] );
  if( error>0 && r>1.e-4 ){
    error = sqrt(error)/r;
    return 0;
  }
  error = 1.e10;
  return 1;
}

Int_t KFParticleBase::GetMass( Double_t &m, Double_t &error ) const 
{
  //* Calculate particle mass
  
  // s = sigma^2 of m2/2

  Double_t s = (  fP[3]*fP[3]*fC[9] + fP[4]*fP[4]*fC[14] + fP[5]*fP[5]*fC[20] 
                  + fP[6]*fP[6]*fC[27] 
                +2*( + fP[3]*fP[4]*fC[13] + fP[5]*(fP[3]*fC[18] + fP[4]*fC[19]) 
                     - fP[6]*( fP[3]*fC[24] + fP[4]*fC[25] + fP[5]*fC[26] )   )
                 ); 
//   Double_t m2 = fabs(fP[6]*fP[6] - fP[3]*fP[3] - fP[4]*fP[4] - fP[5]*fP[5]);
//   m  = sqrt(m2);
//   if( m>1.e-10 ){
//     if( s>=0 ){
//       error = sqrt(s)/m;
//       return 0;
//     }
//   }
//   error = 1.e20;
  Double_t m2 = (fP[6]*fP[6] - fP[3]*fP[3] - fP[4]*fP[4] - fP[5]*fP[5]);

  if(m2<0.)
  {
    error = 1.e20;
    m = -sqrt(-m2);
    return 1;
  }

  m  = sqrt(m2);
  if( m>1.e-6 ){
    if( s >= 0 ) {
      error = sqrt(s)/m;
      return 0;
    }
  }
  else {
    error = 1.e20;
    return 0;
  }
  error = 1.e20;

  return 1;
}


Int_t KFParticleBase::GetDecayLength( Double_t &l, Double_t &error ) const 
{
  //* Calculate particle decay length [cm]

  Double_t x = fP[3];
  Double_t y = fP[4];
  Double_t z = fP[5];
  Double_t t = fP[7];
  Double_t x2 = x*x;
  Double_t y2 = y*y;
  Double_t z2 = z*z;
  Double_t p2 = x2+y2+z2;
  l = t*sqrt(p2);
  if( p2>1.e-4){
    error = p2*fC[35] + t*t/p2*(x2*fC[9]+y2*fC[14]+z2*fC[20]
                                + 2*(x*y*fC[13]+x*z*fC[18]+y*z*fC[19]) )
      + 2*t*(x*fC[31]+y*fC[32]+z*fC[33]);
    error = sqrt(fabs(error));
    return 0;
  }
  error = 1.e20;
  return 1;
}

Int_t KFParticleBase::GetDecayLengthXY( Double_t &l, Double_t &error ) const 
{
  //* Calculate particle decay length in XY projection [cm]

  Double_t x = fP[3];
  Double_t y = fP[4];
  Double_t t = fP[7];
  Double_t x2 = x*x;
  Double_t y2 = y*y;
  Double_t pt2 = x2+y2;
  l = t*sqrt(pt2);
  if( pt2>1.e-4){
    error = pt2*fC[35] + t*t/pt2*(x2*fC[9]+y2*fC[14] + 2*x*y*fC[13] )
      + 2*t*(x*fC[31]+y*fC[32]);
    error = sqrt(fabs(error));
    return 0;
  }
  error = 1.e20;
  return 1;
}


Int_t KFParticleBase::GetLifeTime( Double_t &tauC, Double_t &error ) const 
{
  //* Calculate particle decay time [s]

  Double_t m, dm;
  GetMass( m, dm );
  Double_t cTM = (-fP[3]*fC[31] - fP[4]*fC[32] - fP[5]*fC[33] + fP[6]*fC[34]);
  tauC = fP[7]*m;
  error = m*m*fC[35] + 2*fP[7]*cTM + fP[7]*fP[7]*dm*dm;
  if( error > 0 ){
    error = sqrt( error );
    return 0;
  }
  error = 1.e20;
  return 1;
}


void KFParticleBase::operator +=( const KFParticleBase &Daughter )
{
  //* Add daughter via operator+=

  AddDaughter( Daughter );
}
  
Double_t KFParticleBase::GetSCorrection( const Double_t Part[], const Double_t XYZ[] ) 
{
  //* Get big enough correction for S error to let the particle Part be fitted to XYZ point
  
  Double_t d[3] = { XYZ[0]-Part[0], XYZ[1]-Part[1], XYZ[2]-Part[2] };
  Double_t p2 = Part[3]*Part[3]+Part[4]*Part[4]+Part[5]*Part[5];
//  Double_t sigmaS = (p2>1.e-4) ? ( 10.1+3.*sqrt( d[0]*d[0]+d[1]*d[1]+d[2]*d[2]) )/sqrt(p2) : 1.;
  Double_t sigmaS = (p2>1.e-4) ? ( 0.1+10.*sqrt( d[0]*d[0]+d[1]*d[1]+d[2]*d[2]) )/sqrt(p2) : 1.;
  return sigmaS;
}

void KFParticleBase::GetMeasurement( const Double_t XYZ[], Double_t m[], Double_t V[] ) const
{
  //* Get additional covariances V used during measurement

  Double_t b[3];
  GetFieldValue( XYZ, b );
  const Double_t kCLight =  0.000299792458;
  b[0]*=kCLight; b[1]*=kCLight; b[2]*=kCLight;
// std::cout << "   DStoPoint "<< (GetDStoPoint(XYZ)) << std::endl;
  Transport( GetDStoPoint(XYZ), m, V );
//std::cout << "x " << XYZ[0] << " " << m[0] <<"   y " << XYZ[1] << " " << m[1] <<"   z " << XYZ[2] << " " << m[2] <<std::endl;
  Double_t sigmaS = GetSCorrection( m, XYZ );

  Double_t h[6];

  h[0] = m[3]*sigmaS;
  h[1] = m[4]*sigmaS;
  h[2] = m[5]*sigmaS;
  h[3] = ( h[1]*b[2]-h[2]*b[1] )*GetQ();
  h[4] = ( h[2]*b[0]-h[0]*b[2] )*GetQ();
  h[5] = ( h[0]*b[1]-h[1]*b[0] )*GetQ();
    
  V[ 0]+= h[0]*h[0];
  V[ 1]+= h[1]*h[0];
  V[ 2]+= h[1]*h[1];
  V[ 3]+= h[2]*h[0];
  V[ 4]+= h[2]*h[1];
  V[ 5]+= h[2]*h[2];

  V[ 6]+= h[3]*h[0];
  V[ 7]+= h[3]*h[1];
  V[ 8]+= h[3]*h[2];
  V[ 9]+= h[3]*h[3];

  V[10]+= h[4]*h[0];
  V[11]+= h[4]*h[1];
  V[12]+= h[4]*h[2];
  V[13]+= h[4]*h[3];
  V[14]+= h[4]*h[4];

  V[15]+= h[5]*h[0];
  V[16]+= h[5]*h[1];
  V[17]+= h[5]*h[2];
  V[18]+= h[5]*h[3];
  V[19]+= h[5]*h[4];
  V[20]+= h[5]*h[5];
}

void KFParticleBase::AddDaughter( const KFParticleBase &Daughter )
{
  if( fNDF<-1 ){ // first daughter -> just copy
    fNDF   = -1;
    fQ     =  Daughter.GetQ();
    for( Int_t i=0; i<7; i++) fP[i] = Daughter.fP[i];
    for( Int_t i=0; i<28; i++) fC[i] = Daughter.fC[i];
    fSFromDecay = 0;
    fMassHypo = Daughter.fMassHypo;
    SumDaughterMass = Daughter.SumDaughterMass;
    return;
  }

  if(fConstructMethod == 0)
    AddDaughterWithEnergyFit(Daughter);
  else if(fConstructMethod == 1)
    AddDaughterWithEnergyCalc(Daughter);
  else if(fConstructMethod == 2)
    AddDaughterWithEnergyFitMC(Daughter);

  SumDaughterMass += Daughter.SumDaughterMass;
  fMassHypo = -1;
}

void KFParticleBase::AddDaughterWithEnergyFit( const KFParticleBase &Daughter )
{
  //* Energy considered as an independent veriable, fitted independently from momentum, without any constraints on mass

  //* Add daughter 

  TransportToDecayVertex();

  Double_t b[3]; 
  Int_t maxIter = 1;

  if( !fIsLinearized ){
    if( fNDF==-1 ){
      Double_t ds, ds1;
      GetDStoParticle(Daughter, ds, ds1);      
      TransportToDS( ds );
      Double_t m[8];
      Double_t mCd[36];       
      Daughter.Transport( ds1, m, mCd );    
      fVtxGuess[0] = .5*( fP[0] + m[0] );
      fVtxGuess[1] = .5*( fP[1] + m[1] );
      fVtxGuess[2] = .5*( fP[2] + m[2] );
    } else {
      fVtxGuess[0] = fP[0];
      fVtxGuess[1] = fP[1];
      fVtxGuess[2] = fP[2]; 
    }
    maxIter = 3;
  }

  for( Int_t iter=0; iter<maxIter; iter++ ){

    {
      GetFieldValue( fVtxGuess, b );
      const Double_t kCLight =  0.000299792458;
      b[0]*=kCLight; b[1]*=kCLight; b[2]*=kCLight;
    }

    Double_t *ffP = fP, *ffC = fC, tmpP[8], tmpC[36];
    if( fNDF==-1 ){            
      GetMeasurement( fVtxGuess, tmpP, tmpC );
      ffP = tmpP;
      ffC = tmpC;
    }

    Double_t m[8], mV[36];

    if( Daughter.fC[35]>0 ){
      Daughter.GetMeasurement( fVtxGuess, m, mV );
    } else {
      for( Int_t i=0; i<8; i++ ) m[i] = Daughter.fP[i];
      for( Int_t i=0; i<36; i++ ) mV[i] = Daughter.fC[i];
    }
    //*

    Double_t mS[6];
    {
      Double_t mSi[6] = { ffC[0]+mV[0], 
                          ffC[1]+mV[1], ffC[2]+mV[2], 
                          ffC[3]+mV[3], ffC[4]+mV[4], ffC[5]+mV[5] };

      mS[0] = mSi[2]*mSi[5] - mSi[4]*mSi[4];
      mS[1] = mSi[3]*mSi[4] - mSi[1]*mSi[5];
      mS[2] = mSi[0]*mSi[5] - mSi[3]*mSi[3];
      mS[3] = mSi[1]*mSi[4] - mSi[2]*mSi[3];
      mS[4] = mSi[1]*mSi[3] - mSi[0]*mSi[4];
      mS[5] = mSi[0]*mSi[2] - mSi[1]*mSi[1];     

      Double_t s = ( mSi[0]*mS[0] + mSi[1]*mS[1] + mSi[3]*mS[3] );      
      s = ( fabs(s) > 1.E-20 )  ?1./s :0;         
      mS[0]*=s;
      mS[1]*=s;
      mS[2]*=s;
      mS[3]*=s;
      mS[4]*=s;
      mS[5]*=s;
    }
    //* Residual (measured - estimated)

    Double_t zeta[3] = { m[0]-ffP[0], m[1]-ffP[1], m[2]-ffP[2] };    

    //* CHt = CH' - D'

    Double_t mCHt0[7], mCHt1[7], mCHt2[7];

    mCHt0[0]=ffC[ 0] ;       mCHt1[0]=ffC[ 1] ;       mCHt2[0]=ffC[ 3] ;
    mCHt0[1]=ffC[ 1] ;       mCHt1[1]=ffC[ 2] ;       mCHt2[1]=ffC[ 4] ;
    mCHt0[2]=ffC[ 3] ;       mCHt1[2]=ffC[ 4] ;       mCHt2[2]=ffC[ 5] ;
    mCHt0[3]=ffC[ 6]-mV[ 6]; mCHt1[3]=ffC[ 7]-mV[ 7]; mCHt2[3]=ffC[ 8]-mV[ 8];
    mCHt0[4]=ffC[10]-mV[10]; mCHt1[4]=ffC[11]-mV[11]; mCHt2[4]=ffC[12]-mV[12];
    mCHt0[5]=ffC[15]-mV[15]; mCHt1[5]=ffC[16]-mV[16]; mCHt2[5]=ffC[17]-mV[17];
    mCHt0[6]=ffC[21]-mV[21]; mCHt1[6]=ffC[22]-mV[22]; mCHt2[6]=ffC[23]-mV[23];
  
    //* Kalman gain K = mCH'*S
    
    Double_t k0[7], k1[7], k2[7];
    
    for(Int_t i=0;i<7;++i){
      k0[i] = mCHt0[i]*mS[0] + mCHt1[i]*mS[1] + mCHt2[i]*mS[3];
      k1[i] = mCHt0[i]*mS[1] + mCHt1[i]*mS[2] + mCHt2[i]*mS[4];
      k2[i] = mCHt0[i]*mS[3] + mCHt1[i]*mS[4] + mCHt2[i]*mS[5];
    }

   //* New estimation of the vertex position 

    if( iter<maxIter-1 ){
      for(Int_t i=0; i<3; ++i) 
        fVtxGuess[i]= ffP[i] + k0[i]*zeta[0]+k1[i]*zeta[1]+k2[i]*zeta[2];
      continue;
    }

    // last itearation -> update the particle

    //* Add the daughter momentum to the particle momentum
    
    ffP[ 3] += m[ 3];
    ffP[ 4] += m[ 4];
    ffP[ 5] += m[ 5];
    ffP[ 6] += m[ 6];
  
    ffC[ 9] += mV[ 9];
    ffC[13] += mV[13];
    ffC[14] += mV[14];
    ffC[18] += mV[18];
    ffC[19] += mV[19];
    ffC[20] += mV[20];
    ffC[24] += mV[24];
    ffC[25] += mV[25];
    ffC[26] += mV[26];
    ffC[27] += mV[27];
    
 
   //* New estimation of the vertex position r += K*zeta
    
    for(Int_t i=0;i<7;++i) 
      fP[i] = ffP[i] + k0[i]*zeta[0] + k1[i]*zeta[1] + k2[i]*zeta[2];
    
    //* New covariance matrix C -= K*(mCH')'

    for(Int_t i=0, k=0;i<7;++i){
      for(Int_t j=0;j<=i;++j,++k){
        fC[k] = ffC[k] - (k0[i]*mCHt0[j] + k1[i]*mCHt1[j] + k2[i]*mCHt2[j] );
      }
    }
  
    //* Calculate Chi^2 

    fNDF  += 2;
    fQ    +=  Daughter.GetQ();
    fSFromDecay = 0;    
    fChi2 += (mS[0]*zeta[0] + mS[1]*zeta[1] + mS[3]*zeta[2])*zeta[0]
      +      (mS[1]*zeta[0] + mS[2]*zeta[1] + mS[4]*zeta[2])*zeta[1]
      +      (mS[3]*zeta[0] + mS[4]*zeta[1] + mS[5]*zeta[2])*zeta[2];     

  }
}

void KFParticleBase::AddDaughterWithEnergyCalc( const KFParticleBase &Daughter )
{
  //* Energy considered as a dependent variable, calculated from the momentum and mass hypothesis

  //* Add daughter 

  TransportToDecayVertex();

  Double_t b[3]; 
  Int_t maxIter = 1;

  if( !fIsLinearized ){
    if( fNDF==-1 ){
      Double_t ds, ds1;
      GetDStoParticle(Daughter, ds, ds1);      
      TransportToDS( ds );
      Double_t m[8];
      Double_t mCd[36];       
      Daughter.Transport( ds1, m, mCd );    
      fVtxGuess[0] = .5*( fP[0] + m[0] );
      fVtxGuess[1] = .5*( fP[1] + m[1] );
      fVtxGuess[2] = .5*( fP[2] + m[2] );
    } else {
      fVtxGuess[0] = fP[0];
      fVtxGuess[1] = fP[1];
      fVtxGuess[2] = fP[2]; 
    }
    maxIter = 3;
  }

  for( Int_t iter=0; iter<maxIter; iter++ ){

    {
      GetFieldValue( fVtxGuess, b );
      const Double_t kCLight =  0.000299792458;
      b[0]*=kCLight; b[1]*=kCLight; b[2]*=kCLight;
    }

    Double_t *ffP = fP, *ffC = fC, tmpP[8], tmpC[36];
    if( fNDF==-1 ){            
      GetMeasurement( fVtxGuess, tmpP, tmpC );
      ffP = tmpP;
      ffC = tmpC;
    }

    Double_t m[8], mV[36];

    if( Daughter.fC[35]>0 ){
      Daughter.GetMeasurement( fVtxGuess, m, mV );
    } else {
      for( Int_t i=0; i<8; i++ ) m[i] = Daughter.fP[i];
      for( Int_t i=0; i<36; i++ ) mV[i] = Daughter.fC[i];
    }

    double massMf2 = m[6]*m[6] - (m[3]*m[3] + m[4]*m[4] + m[5]*m[5]);
    double massRf2 = fP[6]*fP[6] - (fP[3]*fP[3] + fP[4]*fP[4] + fP[5]*fP[5]);

    //*

    Double_t mS[6];
    {
      Double_t mSi[6] = { ffC[0]+mV[0], 
                          ffC[1]+mV[1], ffC[2]+mV[2], 
                          ffC[3]+mV[3], ffC[4]+mV[4], ffC[5]+mV[5] };

      mS[0] = mSi[2]*mSi[5] - mSi[4]*mSi[4];
      mS[1] = mSi[3]*mSi[4] - mSi[1]*mSi[5];
      mS[2] = mSi[0]*mSi[5] - mSi[3]*mSi[3];
      mS[3] = mSi[1]*mSi[4] - mSi[2]*mSi[3];
      mS[4] = mSi[1]*mSi[3] - mSi[0]*mSi[4];
      mS[5] = mSi[0]*mSi[2] - mSi[1]*mSi[1];     

      Double_t s = ( mSi[0]*mS[0] + mSi[1]*mS[1] + mSi[3]*mS[3] );      

      s = ( s > 1.E-20 )  ?1./s :0;       
      mS[0]*=s;
      mS[1]*=s;
      mS[2]*=s;
      mS[3]*=s;
      mS[4]*=s;
      mS[5]*=s;
    }

    //* Residual (measured - estimated)

    Double_t zeta[3] = { m[0]-ffP[0], m[1]-ffP[1], m[2]-ffP[2] };    

    //* CHt = CH' - D'

    Double_t mCHt0[6], mCHt1[6], mCHt2[6];

    mCHt0[0]=ffC[ 0] ;       mCHt1[0]=ffC[ 1] ;       mCHt2[0]=ffC[ 3] ;
    mCHt0[1]=ffC[ 1] ;       mCHt1[1]=ffC[ 2] ;       mCHt2[1]=ffC[ 4] ;
    mCHt0[2]=ffC[ 3] ;       mCHt1[2]=ffC[ 4] ;       mCHt2[2]=ffC[ 5] ;
    mCHt0[3]=ffC[ 6]-mV[ 6]; mCHt1[3]=ffC[ 7]-mV[ 7]; mCHt2[3]=ffC[ 8]-mV[ 8];
    mCHt0[4]=ffC[10]-mV[10]; mCHt1[4]=ffC[11]-mV[11]; mCHt2[4]=ffC[12]-mV[12];
    mCHt0[5]=ffC[15]-mV[15]; mCHt1[5]=ffC[16]-mV[16]; mCHt2[5]=ffC[17]-mV[17];

    //* Kalman gain K = mCH'*S

    Double_t k0[6], k1[6], k2[6];

    for(Int_t i=0;i<6;++i){
      k0[i] = mCHt0[i]*mS[0] + mCHt1[i]*mS[1] + mCHt2[i]*mS[3];
      k1[i] = mCHt0[i]*mS[1] + mCHt1[i]*mS[2] + mCHt2[i]*mS[4];
      k2[i] = mCHt0[i]*mS[3] + mCHt1[i]*mS[4] + mCHt2[i]*mS[5];
    }

   //* New estimation of the vertex position 

    if( iter<maxIter-1 ){
      for(Int_t i=0; i<3; ++i) 
        fVtxGuess[i]= ffP[i] + k0[i]*zeta[0]+k1[i]*zeta[1]+k2[i]*zeta[2];
      continue;
    }

   //* find mf and mVf - optimum value of the measurement and its covariance matrix
    //* mVHt = V*H'
    Double_t mVHt0[6], mVHt1[6], mVHt2[6];

    mVHt0[0]= mV[ 0] ; mVHt1[0]= mV[ 1] ; mVHt2[0]= mV[ 3] ;
    mVHt0[1]= mV[ 1] ; mVHt1[1]= mV[ 2] ; mVHt2[1]= mV[ 4] ;
    mVHt0[2]= mV[ 3] ; mVHt1[2]= mV[ 4] ; mVHt2[2]= mV[ 5] ;
    mVHt0[3]= mV[ 6] ; mVHt1[3]= mV[ 7] ; mVHt2[3]= mV[ 8] ;
    mVHt0[4]= mV[10] ; mVHt1[4]= mV[11] ; mVHt2[4]= mV[12] ;
    mVHt0[5]= mV[15] ; mVHt1[5]= mV[16] ; mVHt2[5]= mV[17] ;

    //* Kalman gain Km = mCH'*S

    Double_t km0[6], km1[6], km2[6];

    for(Int_t i=0;i<6;++i){
      km0[i] = mVHt0[i]*mS[0] + mVHt1[i]*mS[1] + mVHt2[i]*mS[3];
      km1[i] = mVHt0[i]*mS[1] + mVHt1[i]*mS[2] + mVHt2[i]*mS[4];
      km2[i] = mVHt0[i]*mS[3] + mVHt1[i]*mS[4] + mVHt2[i]*mS[5];
    }

    Double_t mf[7] = { m[0], m[1], m[2], m[3], m[4], m[5], m[6] };

    for(Int_t i=0;i<6;++i) 
      mf[i] = mf[i] - km0[i]*zeta[0] - km1[i]*zeta[1] - km2[i]*zeta[2];

    Double_t energyMf = sqrt( massMf2 + (mf[3]*mf[3] + mf[4]*mf[4] + mf[5]*mf[5]) );

    Double_t mVf[28];
    for(Int_t iC=0; iC<28; iC++)
      mVf[iC] = mV[iC];

    //* hmf = d(energyMf)/d(mf)
    Double_t hmf[7];
    if( fabs(energyMf) < 1.e-10) hmf[3] = 0; else hmf[3] = mf[3]/energyMf;
    if( fabs(energyMf) < 1.e-10) hmf[4] = 0; else hmf[4] = mf[4]/energyMf;
    if( fabs(energyMf) < 1.e-10) hmf[5] = 0; else hmf[5] = mf[5]/energyMf;
//    if( fabs(energyMf) < 1.e-10) hmf[6] = 0; else hmf[6] = mf[6]/energyMf;
    hmf[6] = 0;

    for(Int_t i=0, k=0;i<6;++i){
      for(Int_t j=0;j<=i;++j,++k){
        mVf[k] = mVf[k] - (km0[i]*mVHt0[j] + km1[i]*mVHt1[j] + km2[i]*mVHt2[j] );
      }
    }
    Double_t mVf24 = mVf[24], mVf25 = mVf[25], mVf26 = mVf[26];
    mVf[21] = mVf[6 ]*hmf[3] + mVf[10]*hmf[4] + mVf[15]*hmf[5] + mVf[21]*hmf[6];
    mVf[22] = mVf[7 ]*hmf[3] + mVf[11]*hmf[4] + mVf[16]*hmf[5] + mVf[22]*hmf[6];
    mVf[23] = mVf[8 ]*hmf[3] + mVf[12]*hmf[4] + mVf[17]*hmf[5] + mVf[23]*hmf[6];
    mVf[24] = mVf[9 ]*hmf[3] + mVf[13]*hmf[4] + mVf[18]*hmf[5] + mVf[24]*hmf[6];
    mVf[25] = mVf[13]*hmf[3] + mVf[14]*hmf[4] + mVf[19]*hmf[5] + mVf[25]*hmf[6];
    mVf[26] = mVf[18]*hmf[3] + mVf[19]*hmf[4] + mVf[20]*hmf[5] + mVf[26]*hmf[6];
    mVf[27] = mVf[24]*hmf[3] + mVf[25]*hmf[4] + mVf[26]*hmf[5] + (mVf24*hmf[3] + mVf25*hmf[4] + mVf26*hmf[5] + mVf[27]*hmf[6])*hmf[6]; //here mVf[] are already modified

    mf[6] = energyMf;

    //* find rf and mCf - optimum value of the measurement and its covariance matrix

    //* mCCHt = C*H'
    Double_t mCCHt0[6], mCCHt1[6], mCCHt2[6];

    mCCHt0[0]=ffC[ 0]; mCCHt1[0]=ffC[ 1]; mCCHt2[0]=ffC[ 3];
    mCCHt0[1]=ffC[ 1]; mCCHt1[1]=ffC[ 2]; mCCHt2[1]=ffC[ 4];
    mCCHt0[2]=ffC[ 3]; mCCHt1[2]=ffC[ 4]; mCCHt2[2]=ffC[ 5];
    mCCHt0[3]=ffC[ 6]; mCCHt1[3]=ffC[ 7]; mCCHt2[3]=ffC[ 8];
    mCCHt0[4]=ffC[10]; mCCHt1[4]=ffC[11]; mCCHt2[4]=ffC[12];
    mCCHt0[5]=ffC[15]; mCCHt1[5]=ffC[16]; mCCHt2[5]=ffC[17];

    //* Kalman gain Krf = mCH'*S

    Double_t krf0[6], krf1[6], krf2[6];

    for(Int_t i=0;i<6;++i){
      krf0[i] = mCCHt0[i]*mS[0] + mCCHt1[i]*mS[1] + mCCHt2[i]*mS[3];
      krf1[i] = mCCHt0[i]*mS[1] + mCCHt1[i]*mS[2] + mCCHt2[i]*mS[4];
      krf2[i] = mCCHt0[i]*mS[3] + mCCHt1[i]*mS[4] + mCCHt2[i]*mS[5];
    }
    Double_t rf[7] = { ffP[0], ffP[1], ffP[2], ffP[3], ffP[4], ffP[5], ffP[6] };

    for(Int_t i=0;i<6;++i) 
      rf[i] = rf[i] + krf0[i]*zeta[0] + krf1[i]*zeta[1] + krf2[i]*zeta[2];

    Double_t energyRf = sqrt( massRf2 + (rf[3]*rf[3] + rf[4]*rf[4] + rf[5]*rf[5]) );

    Double_t mCf[28];
    for(Int_t iC=0; iC<28; iC++)
      mCf[iC] = ffC[iC];
    //* hrf = d(Erf)/d(rf)
    Double_t hrf[7];
    if( fabs(energyRf) < 1.e-10) hrf[3] = 0; else hrf[3] = rf[3]/energyRf;
    if( fabs(energyRf) < 1.e-10) hrf[4] = 0; else hrf[4] = rf[4]/energyRf;
    if( fabs(energyRf) < 1.e-10) hrf[5] = 0; else hrf[5] = rf[5]/energyRf;
//    if( fabs(energyRf) < 1.e-10) hrf[6] = 0; else hrf[6] = rf[6]/energyRf;
    hrf[6] = 0;

    for(Int_t i=0, k=0;i<6;++i){
      for(Int_t j=0;j<=i;++j,++k){
        mCf[k] = mCf[k] - (krf0[i]*mCCHt0[j] + krf1[i]*mCCHt1[j] + krf2[i]*mCCHt2[j] );
      }
    }
    Double_t mCf24 = mCf[24], mCf25 = mCf[25], mCf26 = mCf[26];
    mCf[21] = mCf[6 ]*hrf[3] + mCf[10]*hrf[4] + mCf[15]*hrf[5] + mCf[21]*hrf[6];
    mCf[22] = mCf[7 ]*hrf[3] + mCf[11]*hrf[4] + mCf[16]*hrf[5] + mCf[22]*hrf[6];
    mCf[23] = mCf[8 ]*hrf[3] + mCf[12]*hrf[4] + mCf[17]*hrf[5] + mCf[23]*hrf[6];
    mCf[24] = mCf[9 ]*hrf[3] + mCf[13]*hrf[4] + mCf[18]*hrf[5] + mCf[24]*hrf[6];
    mCf[25] = mCf[13]*hrf[3] + mCf[14]*hrf[4] + mCf[19]*hrf[5] + mCf[25]*hrf[6];
    mCf[26] = mCf[18]*hrf[3] + mCf[19]*hrf[4] + mCf[20]*hrf[5] + mCf[26]*hrf[6];
    mCf[27] = mCf[24]*hrf[3] + mCf[25]*hrf[4] + mCf[26]*hrf[5] + (mCf24*hrf[3] + mCf25*hrf[4] + mCf26*hrf[5] + mCf[27]*hrf[6])*hrf[6]; //here mCf[] are already modified

    for(Int_t iC=21; iC<28; iC++)
    {
      ffC[iC] = mCf[iC];
      mV[iC]  = mVf[iC];
    }

    fP[6] = energyRf + energyMf;
    rf[6] = energyRf;

    //Double_t Dvv[3][3]; do not need this
    Double_t mDvp[3][3];
    Double_t mDpv[3][3];
    Double_t mDpp[3][3];
    Double_t mDe[7];

    for(int i=0; i<3; i++)
    {
      for(int j=0; j<3; j++)
      {
        mDvp[i][j] = km0[i+3]*mCCHt0[j] + km1[i+3]*mCCHt1[j] + km2[i+3]*mCCHt2[j];
        mDpv[i][j] = km0[i]*mCCHt0[j+3] + km1[i]*mCCHt1[j+3] + km2[i]*mCCHt2[j+3];
        mDpp[i][j] = km0[i+3]*mCCHt0[j+3] + km1[i+3]*mCCHt1[j+3] + km2[i+3]*mCCHt2[j+3];
      }
    }

    mDe[0] = hmf[3]*mDvp[0][0] + hmf[4]*mDvp[1][0] + hmf[5]*mDvp[2][0];
    mDe[1] = hmf[3]*mDvp[0][1] + hmf[4]*mDvp[1][1] + hmf[5]*mDvp[2][1];
    mDe[2] = hmf[3]*mDvp[0][2] + hmf[4]*mDvp[1][2] + hmf[5]*mDvp[2][2];
    mDe[3] = hmf[3]*mDpp[0][0] + hmf[4]*mDpp[1][0] + hmf[5]*mDpp[2][0];
    mDe[4] = hmf[3]*mDpp[0][1] + hmf[4]*mDpp[1][1] + hmf[5]*mDpp[2][1];
    mDe[5] = hmf[3]*mDpp[0][2] + hmf[4]*mDpp[1][2] + hmf[5]*mDpp[2][2];
    mDe[6] = 2*(mDe[3]*hrf[3] + mDe[4]*hrf[4] + mDe[5]*hrf[5]);

    // last itearation -> update the particle

    //* Add the daughter momentum to the particle momentum

    ffP[ 3] += m[ 3];
    ffP[ 4] += m[ 4];
    ffP[ 5] += m[ 5];

    ffC[ 9] += mV[ 9];
    ffC[13] += mV[13];
    ffC[14] += mV[14];
    ffC[18] += mV[18];
    ffC[19] += mV[19];
    ffC[20] += mV[20];
    ffC[24] += mV[24];
    ffC[25] += mV[25];
    ffC[26] += mV[26];
    ffC[27] += mV[27];

    ffC[21] += mDe[0];
    ffC[22] += mDe[1];
    ffC[23] += mDe[2];
    ffC[24] += mDe[3];
    ffC[25] += mDe[4];
    ffC[26] += mDe[5];
    ffC[27] += mDe[6];

   //* New estimation of the vertex position r += K*zeta

    for(Int_t i=0;i<6;++i) 
      fP[i] = ffP[i] + k0[i]*zeta[0] + k1[i]*zeta[1] + k2[i]*zeta[2];

    //* New covariance matrix C -= K*(mCH')'

    for(Int_t i=0, k=0;i<6;++i){
      for(Int_t j=0;j<=i;++j,++k){
        fC[k] = ffC[k] - (k0[i]*mCHt0[j] + k1[i]*mCHt1[j] + k2[i]*mCHt2[j] );
      }
    }

    for(int i=21; i<28; i++) fC[i] = ffC[i];

    //* Calculate Chi^2 

    fNDF  += 2;
    fQ    +=  Daughter.GetQ();
    fSFromDecay = 0;    
    fChi2 += (mS[0]*zeta[0] + mS[1]*zeta[1] + mS[3]*zeta[2])*zeta[0]
      +      (mS[1]*zeta[0] + mS[2]*zeta[1] + mS[4]*zeta[2])*zeta[1]
      +      (mS[3]*zeta[0] + mS[4]*zeta[1] + mS[5]*zeta[2])*zeta[2];     
  }
}

void KFParticleBase::AddDaughterWithEnergyFitMC( const KFParticleBase &Daughter )
{
  //* Energy considered as an independent variable, fitted independently from momentum, without any constraints on mass

  //* Add daughter 

  TransportToDecayVertex();

  Double_t b[3]; 
  Int_t maxIter = 1;

  if( !fIsLinearized ){
    if( fNDF==-1 ){
      Double_t ds, ds1;
      GetDStoParticle(Daughter, ds, ds1);      
      TransportToDS( ds );
      Double_t m[8];
      Double_t mCd[36];       
      Daughter.Transport( ds1, m, mCd );    
      fVtxGuess[0] = .5*( fP[0] + m[0] );
      fVtxGuess[1] = .5*( fP[1] + m[1] );
      fVtxGuess[2] = .5*( fP[2] + m[2] );
    } else {
      fVtxGuess[0] = fP[0];
      fVtxGuess[1] = fP[1];
      fVtxGuess[2] = fP[2]; 
    }
    maxIter = 3;
  }

  for( Int_t iter=0; iter<maxIter; iter++ ){

    {
      GetFieldValue( fVtxGuess, b );
      const Double_t kCLight =  0.000299792458;
      b[0]*=kCLight; b[1]*=kCLight; b[2]*=kCLight;
    }

    Double_t *ffP = fP, *ffC = fC, tmpP[8], tmpC[36];
    if( fNDF==-1 ){            
      GetMeasurement( fVtxGuess, tmpP, tmpC );
      ffP = tmpP;
      ffC = tmpC;
    }
    Double_t m[8], mV[36];

    if( Daughter.fC[35]>0 ){
      Daughter.GetMeasurement( fVtxGuess, m, mV );
    } else {
      for( Int_t i=0; i<8; i++ ) m[i] = Daughter.fP[i];
      for( Int_t i=0; i<36; i++ ) mV[i] = Daughter.fC[i];
    }
    //*

    Double_t mS[6];
    {
      Double_t mSi[6] = { ffC[0]+mV[0], 
                          ffC[1]+mV[1], ffC[2]+mV[2], 
                          ffC[3]+mV[3], ffC[4]+mV[4], ffC[5]+mV[5] };
     
      mS[0] = mSi[2]*mSi[5] - mSi[4]*mSi[4];
      mS[1] = mSi[3]*mSi[4] - mSi[1]*mSi[5];
      mS[2] = mSi[0]*mSi[5] - mSi[3]*mSi[3];
      mS[3] = mSi[1]*mSi[4] - mSi[2]*mSi[3];
      mS[4] = mSi[1]*mSi[3] - mSi[0]*mSi[4];
      mS[5] = mSi[0]*mSi[2] - mSi[1]*mSi[1];     
      
      Double_t s = ( mSi[0]*mS[0] + mSi[1]*mS[1] + mSi[3]*mS[3] );      

      s = ( s > 1.E-20 )  ?1./s :0;       
      mS[0]*=s;
      mS[1]*=s;
      mS[2]*=s;
      mS[3]*=s;
      mS[4]*=s;
      mS[5]*=s;
    }
    //* Residual (measured - estimated)
    
    Double_t zeta[3] = { m[0]-ffP[0], m[1]-ffP[1], m[2]-ffP[2] };    

    
    //* CHt = CH'
    
    Double_t mCHt0[7], mCHt1[7], mCHt2[7];
    
    mCHt0[0]=ffC[ 0] ; mCHt1[0]=ffC[ 1] ; mCHt2[0]=ffC[ 3] ;
    mCHt0[1]=ffC[ 1] ; mCHt1[1]=ffC[ 2] ; mCHt2[1]=ffC[ 4] ;
    mCHt0[2]=ffC[ 3] ; mCHt1[2]=ffC[ 4] ; mCHt2[2]=ffC[ 5] ;
    mCHt0[3]=ffC[ 6] ; mCHt1[3]=ffC[ 7] ; mCHt2[3]=ffC[ 8] ;
    mCHt0[4]=ffC[10] ; mCHt1[4]=ffC[11] ; mCHt2[4]=ffC[12] ;
    mCHt0[5]=ffC[15] ; mCHt1[5]=ffC[16] ; mCHt2[5]=ffC[17] ;
    mCHt0[6]=ffC[21] ; mCHt1[6]=ffC[22] ; mCHt2[6]=ffC[23] ;
  
    //* Kalman gain K = mCH'*S
    
    Double_t k0[7], k1[7], k2[7];
    
    for(Int_t i=0;i<7;++i){
      k0[i] = mCHt0[i]*mS[0] + mCHt1[i]*mS[1] + mCHt2[i]*mS[3];
      k1[i] = mCHt0[i]*mS[1] + mCHt1[i]*mS[2] + mCHt2[i]*mS[4];
      k2[i] = mCHt0[i]*mS[3] + mCHt1[i]*mS[4] + mCHt2[i]*mS[5];
    }

   //* New estimation of the vertex position 

    if( iter<maxIter-1 ){
      for(Int_t i=0; i<3; ++i) 
        fVtxGuess[i]= ffP[i] + k0[i]*zeta[0]+k1[i]*zeta[1]+k2[i]*zeta[2];
      continue;
    }

    // last itearation -> update the particle

    //* VHt = VH'
    
    Double_t mVHt0[7], mVHt1[7], mVHt2[7];
    
    mVHt0[0]=mV[ 0] ; mVHt1[0]=mV[ 1] ; mVHt2[0]=mV[ 3] ;
    mVHt0[1]=mV[ 1] ; mVHt1[1]=mV[ 2] ; mVHt2[1]=mV[ 4] ;
    mVHt0[2]=mV[ 3] ; mVHt1[2]=mV[ 4] ; mVHt2[2]=mV[ 5] ;
    mVHt0[3]=mV[ 6] ; mVHt1[3]=mV[ 7] ; mVHt2[3]=mV[ 8] ;
    mVHt0[4]=mV[10] ; mVHt1[4]=mV[11] ; mVHt2[4]=mV[12] ;
    mVHt0[5]=mV[15] ; mVHt1[5]=mV[16] ; mVHt2[5]=mV[17] ;
    mVHt0[6]=mV[21] ; mVHt1[6]=mV[22] ; mVHt2[6]=mV[23] ;
  
    //* Kalman gain Km = mCH'*S
    
    Double_t km0[7], km1[7], km2[7];
    
    for(Int_t i=0;i<7;++i){
      km0[i] = mVHt0[i]*mS[0] + mVHt1[i]*mS[1] + mVHt2[i]*mS[3];
      km1[i] = mVHt0[i]*mS[1] + mVHt1[i]*mS[2] + mVHt2[i]*mS[4];
      km2[i] = mVHt0[i]*mS[3] + mVHt1[i]*mS[4] + mVHt2[i]*mS[5];
    }

    for(Int_t i=0;i<7;++i) 
      ffP[i] = ffP[i] + k0[i]*zeta[0] + k1[i]*zeta[1] + k2[i]*zeta[2];

    for(Int_t i=0;i<7;++i) 
      m[i] = m[i] - km0[i]*zeta[0] - km1[i]*zeta[1] - km2[i]*zeta[2];

    for(Int_t i=0, k=0;i<7;++i){
      for(Int_t j=0;j<=i;++j,++k){
        ffC[k] = ffC[k] - (k0[i]*mCHt0[j] + k1[i]*mCHt1[j] + k2[i]*mCHt2[j] );
      }
    }

    for(Int_t i=0, k=0;i<7;++i){
      for(Int_t j=0;j<=i;++j,++k){
        mV[k] = mV[k] - (km0[i]*mVHt0[j] + km1[i]*mVHt1[j] + km2[i]*mVHt2[j] );
      }
    }

    Double_t mDf[7][7];

    for(Int_t i=0;i<7;++i){
      for(Int_t j=0;j<7;++j){
        mDf[i][j] = (km0[i]*mCHt0[j] + km1[i]*mCHt1[j] + km2[i]*mCHt2[j] );
      }
    }

    Double_t mJ1[7][7], mJ2[7][7];
    for(Int_t iPar1=0; iPar1<7; iPar1++)
    {
      for(Int_t iPar2=0; iPar2<7; iPar2++)
      {
        mJ1[iPar1][iPar2] = 0;
        mJ2[iPar1][iPar2] = 0;
      }
    }

    Double_t mMassParticle  = ffP[6]*ffP[6] - (ffP[3]*ffP[3] + ffP[4]*ffP[4] + ffP[5]*ffP[5]);
    Double_t mMassDaughter  = m[6]*m[6] - (m[3]*m[3] + m[4]*m[4] + m[5]*m[5]);
    if(mMassParticle > 0) mMassParticle = sqrt(mMassParticle);
    if(mMassDaughter > 0) mMassDaughter = sqrt(mMassDaughter);

    if( fMassHypo > -0.5)
      SetMassConstraint(ffP,ffC,mJ1,fMassHypo);
    else if((mMassParticle < SumDaughterMass) || (ffP[6]<0) )
      SetMassConstraint(ffP,ffC,mJ1,SumDaughterMass);

    if(Daughter.fMassHypo > -0.5)
      SetMassConstraint(m,mV,mJ2,Daughter.fMassHypo);
    else if((mMassDaughter < Daughter.SumDaughterMass) || (m[6] < 0) )
      SetMassConstraint(m,mV,mJ2,Daughter.SumDaughterMass);

    Double_t mDJ[7][7];

    for(Int_t i=0; i<7; i++) {
      for(Int_t j=0; j<7; j++) {
        mDJ[i][j] = 0;
        for(Int_t k=0; k<7; k++) {
          mDJ[i][j] += mDf[i][k]*mJ1[j][k];
        }
      }
    }

    for(Int_t i=0; i<7; ++i){
      for(Int_t j=0; j<7; ++j){
        mDf[i][j]=0;
        for(Int_t l=0; l<7; l++){
          mDf[i][j] += mJ2[i][l]*mDJ[l][j];
        }
      }
    }

    //* Add the daughter momentum to the particle momentum

    ffP[ 3] += m[ 3];
    ffP[ 4] += m[ 4];
    ffP[ 5] += m[ 5];
    ffP[ 6] += m[ 6];

    ffC[ 9] += mV[ 9];
    ffC[13] += mV[13];
    ffC[14] += mV[14];
    ffC[18] += mV[18];
    ffC[19] += mV[19];
    ffC[20] += mV[20];
    ffC[24] += mV[24];
    ffC[25] += mV[25];
    ffC[26] += mV[26];
    ffC[27] += mV[27];

    ffC[6 ] += mDf[3][0]; ffC[7 ] += mDf[3][1]; ffC[8 ] += mDf[3][2];
    ffC[10] += mDf[4][0]; ffC[11] += mDf[4][1]; ffC[12] += mDf[4][2];
    ffC[15] += mDf[5][0]; ffC[16] += mDf[5][1]; ffC[17] += mDf[5][2];
    ffC[21] += mDf[6][0]; ffC[22] += mDf[6][1]; ffC[23] += mDf[6][2];

    ffC[9 ] += mDf[3][3] + mDf[3][3];
    ffC[13] += mDf[4][3] + mDf[3][4]; ffC[14] += mDf[4][4] + mDf[4][4];
    ffC[18] += mDf[5][3] + mDf[3][5]; ffC[19] += mDf[5][4] + mDf[4][5]; ffC[20] += mDf[5][5] + mDf[5][5];
    ffC[24] += mDf[6][3] + mDf[3][6]; ffC[25] += mDf[6][4] + mDf[4][6]; ffC[26] += mDf[6][5] + mDf[5][6]; ffC[27] += mDf[6][6] + mDf[6][6];

   //* New estimation of the vertex position r += K*zeta

    for(Int_t i=0;i<7;++i) 
      fP[i] = ffP[i];

    //* New covariance matrix C -= K*(mCH')'

    for(Int_t i=0, k=0;i<7;++i){
      for(Int_t j=0;j<=i;++j,++k){
        fC[k] = ffC[k];
      }
    }
    //* Calculate Chi^2 

    fNDF  += 2;
    fQ    +=  Daughter.GetQ();
    fSFromDecay = 0;    
    fChi2 += (mS[0]*zeta[0] + mS[1]*zeta[1] + mS[3]*zeta[2])*zeta[0]
      +      (mS[1]*zeta[0] + mS[2]*zeta[1] + mS[4]*zeta[2])*zeta[1]
      +      (mS[3]*zeta[0] + mS[4]*zeta[1] + mS[5]*zeta[2])*zeta[2];
  }
}

void KFParticleBase::SetProductionVertex( const KFParticleBase &Vtx )
{
  //* Set production vertex for the particle, when the particle was not used in the vertex fit

  const Double_t *m = Vtx.fP, *mV = Vtx.fC;

  Bool_t noS = ( fC[35]<=0 ); // no decay length allowed

  if( noS ){ 
    TransportToDecayVertex();
    fP[7] = 0;
    fC[28] = fC[29] = fC[30] = fC[31] = fC[32] = fC[33] = fC[34] = fC[35] = 0;
  } else {
    TransportToDS( GetDStoPoint( m ) );
    fP[7] = -fSFromDecay;
    fC[28] = fC[29] = fC[30] = fC[31] = fC[32] = fC[33] = fC[34] = 0;
    fC[35] = 0.1;

    Convert(1);
  }

  Double_t mAi[6];

  InvertSym3( fC, mAi );

  Double_t mB[5][3];

  mB[0][0] = fC[ 6]*mAi[0] + fC[ 7]*mAi[1] + fC[ 8]*mAi[3];
  mB[0][1] = fC[ 6]*mAi[1] + fC[ 7]*mAi[2] + fC[ 8]*mAi[4];
  mB[0][2] = fC[ 6]*mAi[3] + fC[ 7]*mAi[4] + fC[ 8]*mAi[5];

  mB[1][0] = fC[10]*mAi[0] + fC[11]*mAi[1] + fC[12]*mAi[3];
  mB[1][1] = fC[10]*mAi[1] + fC[11]*mAi[2] + fC[12]*mAi[4];
  mB[1][2] = fC[10]*mAi[3] + fC[11]*mAi[4] + fC[12]*mAi[5];

  mB[2][0] = fC[15]*mAi[0] + fC[16]*mAi[1] + fC[17]*mAi[3];
  mB[2][1] = fC[15]*mAi[1] + fC[16]*mAi[2] + fC[17]*mAi[4];
  mB[2][2] = fC[15]*mAi[3] + fC[16]*mAi[4] + fC[17]*mAi[5];

  mB[3][0] = fC[21]*mAi[0] + fC[22]*mAi[1] + fC[23]*mAi[3];
  mB[3][1] = fC[21]*mAi[1] + fC[22]*mAi[2] + fC[23]*mAi[4];
  mB[3][2] = fC[21]*mAi[3] + fC[22]*mAi[4] + fC[23]*mAi[5];

  mB[4][0] = fC[28]*mAi[0] + fC[29]*mAi[1] + fC[30]*mAi[3];
  mB[4][1] = fC[28]*mAi[1] + fC[29]*mAi[2] + fC[30]*mAi[4];
  mB[4][2] = fC[28]*mAi[3] + fC[29]*mAi[4] + fC[30]*mAi[5];

  Double_t z[3] = { m[0]-fP[0], m[1]-fP[1], m[2]-fP[2] };

  {
    Double_t mAVi[6] = { fC[0]-mV[0], fC[1]-mV[1], fC[2]-mV[2], 
                        fC[3]-mV[3], fC[4]-mV[4], fC[5]-mV[5] };
    
    if( !InvertSym3( mAVi, mAVi ) ){

      Double_t dChi2 = ( +(mAVi[0]*z[0] + mAVi[1]*z[1] + mAVi[3]*z[2])*z[0]
                         +(mAVi[1]*z[0] + mAVi[2]*z[1] + mAVi[4]*z[2])*z[1]
                         +(mAVi[3]*z[0] + mAVi[4]*z[1] + mAVi[5]*z[2])*z[2] );
      
      // Take Abs(dChi2) here. Negative value of 'det' or 'dChi2' shows that the particle 
      // was not used in the production vertex fit
      
      fChi2+= fabs( dChi2 );
    }
    fNDF  += 2;
  }
  
  fP[0] = m[0];
  fP[1] = m[1];
  fP[2] = m[2];
  fP[3]+= mB[0][0]*z[0] + mB[0][1]*z[1] + mB[0][2]*z[2];
  fP[4]+= mB[1][0]*z[0] + mB[1][1]*z[1] + mB[1][2]*z[2];
  fP[5]+= mB[2][0]*z[0] + mB[2][1]*z[1] + mB[2][2]*z[2];
  fP[6]+= mB[3][0]*z[0] + mB[3][1]*z[1] + mB[3][2]*z[2];
  fP[7]+= mB[4][0]*z[0] + mB[4][1]*z[1] + mB[4][2]*z[2];
  
  Double_t d0, d1, d2;

  fC[0] = mV[0];
  fC[1] = mV[1];
  fC[2] = mV[2];
  fC[3] = mV[3];
  fC[4] = mV[4];
  fC[5] = mV[5];

  d0= mB[0][0]*mV[0] + mB[0][1]*mV[1] + mB[0][2]*mV[3] - fC[ 6];
  d1= mB[0][0]*mV[1] + mB[0][1]*mV[2] + mB[0][2]*mV[4] - fC[ 7];
  d2= mB[0][0]*mV[3] + mB[0][1]*mV[4] + mB[0][2]*mV[5] - fC[ 8];

  fC[ 6]+= d0;
  fC[ 7]+= d1;
  fC[ 8]+= d2;
  fC[ 9]+= d0*mB[0][0] + d1*mB[0][1] + d2*mB[0][2];

  d0= mB[1][0]*mV[0] + mB[1][1]*mV[1] + mB[1][2]*mV[3] - fC[10];
  d1= mB[1][0]*mV[1] + mB[1][1]*mV[2] + mB[1][2]*mV[4] - fC[11];
  d2= mB[1][0]*mV[3] + mB[1][1]*mV[4] + mB[1][2]*mV[5] - fC[12];

  fC[10]+= d0;
  fC[11]+= d1;
  fC[12]+= d2;
  fC[13]+= d0*mB[0][0] + d1*mB[0][1] + d2*mB[0][2];
  fC[14]+= d0*mB[1][0] + d1*mB[1][1] + d2*mB[1][2];

  d0= mB[2][0]*mV[0] + mB[2][1]*mV[1] + mB[2][2]*mV[3] - fC[15];
  d1= mB[2][0]*mV[1] + mB[2][1]*mV[2] + mB[2][2]*mV[4] - fC[16];
  d2= mB[2][0]*mV[3] + mB[2][1]*mV[4] + mB[2][2]*mV[5] - fC[17];

  fC[15]+= d0;
  fC[16]+= d1;
  fC[17]+= d2;
  fC[18]+= d0*mB[0][0] + d1*mB[0][1] + d2*mB[0][2];
  fC[19]+= d0*mB[1][0] + d1*mB[1][1] + d2*mB[1][2];
  fC[20]+= d0*mB[2][0] + d1*mB[2][1] + d2*mB[2][2];

  d0= mB[3][0]*mV[0] + mB[3][1]*mV[1] + mB[3][2]*mV[3] - fC[21];
  d1= mB[3][0]*mV[1] + mB[3][1]*mV[2] + mB[3][2]*mV[4] - fC[22];
  d2= mB[3][0]*mV[3] + mB[3][1]*mV[4] + mB[3][2]*mV[5] - fC[23];

  fC[21]+= d0;
  fC[22]+= d1;
  fC[23]+= d2;
  fC[24]+= d0*mB[0][0] + d1*mB[0][1] + d2*mB[0][2];
  fC[25]+= d0*mB[1][0] + d1*mB[1][1] + d2*mB[1][2];
  fC[26]+= d0*mB[2][0] + d1*mB[2][1] + d2*mB[2][2];
  fC[27]+= d0*mB[3][0] + d1*mB[3][1] + d2*mB[3][2];

  d0= mB[4][0]*mV[0] + mB[4][1]*mV[1] + mB[4][2]*mV[3] - fC[28];
  d1= mB[4][0]*mV[1] + mB[4][1]*mV[2] + mB[4][2]*mV[4] - fC[29];
  d2= mB[4][0]*mV[3] + mB[4][1]*mV[4] + mB[4][2]*mV[5] - fC[30];

  fC[28]+= d0;
  fC[29]+= d1;
  fC[30]+= d2;
  fC[31]+= d0*mB[0][0] + d1*mB[0][1] + d2*mB[0][2];
  fC[32]+= d0*mB[1][0] + d1*mB[1][1] + d2*mB[1][2];
  fC[33]+= d0*mB[2][0] + d1*mB[2][1] + d2*mB[2][2];
  fC[34]+= d0*mB[3][0] + d1*mB[3][1] + d2*mB[3][2];
  fC[35]+= d0*mB[4][0] + d1*mB[4][1] + d2*mB[4][2];
  
  if( noS ){ 
    fP[7] = 0;
    fC[28] = fC[29] = fC[30] = fC[31] = fC[32] = fC[33] = fC[34] = fC[35] = 0;
  } else {
    TransportToDS( fP[7] );
    Convert(0);
  }

  fSFromDecay = 0;
}

void KFParticleBase::SetMassConstraint( Double_t *mP, Double_t *mC, Double_t mJ[7][7], Double_t mass )
{
  //* Set nonlinear mass constraint (Mass) on the state vector mP with a covariance matrix mC.
  
  const Double_t energy2 = mP[6]*mP[6], p2 = mP[3]*mP[3]+mP[4]*mP[4]+mP[5]*mP[5], mass2 = mass*mass;

  const Double_t a = energy2 - p2 + 2.*mass2;
  const Double_t b = -2.*(energy2 + p2);
  const Double_t c = energy2 - p2 - mass2;

  Double_t lambda = 0;
  if(fabs(b) > 1.e-10) lambda = -c / b;

  Double_t d = 4.*energy2*p2 - mass2*(energy2-p2-2.*mass2);
  if(d>=0 && fabs(a) > 1.e-10) lambda = (energy2 + p2 - sqrt(d))/a;

  if(mP[6] < 0) //If energy < 0 we need a lambda < 0
    lambda = -1000000.; //Empirical, a better solution should be found

  Int_t iIter=0;
  for(iIter=0; iIter<100; iIter++)
  {
    Double_t lambda2 = lambda*lambda;
    Double_t lambda4 = lambda2*lambda2;

    Double_t lambda0 = lambda;

    Double_t f  = -mass2 * lambda4 + a*lambda2 + b*lambda + c;
    Double_t df = -4.*mass2 * lambda2*lambda + 2.*a*lambda + b;
    if(fabs(df) < 1.e-10) break;
    lambda -= f/df;
    if(fabs(lambda0 - lambda) < 1.e-8) break;
  }

  const Double_t lpi = 1./(1. + lambda);
  const Double_t lmi = 1./(1. - lambda);
  const Double_t lp2i = lpi*lpi;
  const Double_t lm2i = lmi*lmi;

  Double_t lambda2 = lambda*lambda;

  Double_t dfl  = -4.*mass2 * lambda2*lambda + 2.*a*lambda + b;
  Double_t dfx[7] = {0};//,0,0,0};
  dfx[0] = -2.*(1. + lambda)*(1. + lambda)*mP[3];
  dfx[1] = -2.*(1. + lambda)*(1. + lambda)*mP[4];
  dfx[2] = -2.*(1. + lambda)*(1. + lambda)*mP[5];
  dfx[3] = 2.*(1. - lambda)*(1. - lambda)*mP[6];
  Double_t dlx[4] = {1,1,1,1};
  if(fabs(dfl) > 1.e-10 )
  {
    for(int i=0; i<4; i++)
      dlx[i] = -dfx[i] / dfl;
  }

  Double_t dxx[4] = {mP[3]*lm2i, mP[4]*lm2i, mP[5]*lm2i, -mP[6]*lp2i};

  for(Int_t i=0; i<7; i++)
    for(Int_t j=0; j<7; j++)
      mJ[i][j]=0;
  mJ[0][0] = 1.;
  mJ[1][1] = 1.;
  mJ[2][2] = 1.;

  for(Int_t i=3; i<7; i++)
    for(Int_t j=3; j<7; j++)
      mJ[i][j] = dlx[j-3]*dxx[i-3];

  for(Int_t i=3; i<6; i++)
    mJ[i][i] += lmi;
  mJ[6][6] += lpi;

  Double_t mCJ[7][7];

  for(Int_t i=0; i<7; i++) {
    for(Int_t j=0; j<7; j++) {
      mCJ[i][j] = 0;
      for(Int_t k=0; k<7; k++) {
        mCJ[i][j] += mC[IJ(i,k)]*mJ[j][k];
      }
    }
  }

  for(Int_t i=0; i<7; ++i){
    for(Int_t j=0; j<=i; ++j){
      mC[IJ(i,j)]=0;
      for(Int_t l=0; l<7; l++){
        mC[IJ(i,j)] += mJ[i][l]*mCJ[l][j];
      }
    }
  }

  mP[3] *= lmi;
  mP[4] *= lmi;
  mP[5] *= lmi;
  mP[6] *= lpi;
}

void KFParticleBase::SetNonlinearMassConstraint( Double_t mass )
{
  //* Set nonlinear mass constraint (mass)

  Double_t mJ[7][7];
  SetMassConstraint( fP, fC, mJ, mass );
  fMassHypo = mass;
  SumDaughterMass = mass;
}

void KFParticleBase::SetMassConstraint( Double_t Mass, Double_t SigmaMass )
{  
  //* Set hard( SigmaMass=0 ) or soft (SigmaMass>0) mass constraint 

  fMassHypo = Mass;
  SumDaughterMass = Mass;

  Double_t m2 = Mass*Mass;            // measurement, weighted by Mass 
  Double_t s2 = m2*SigmaMass*SigmaMass; // sigma^2

  Double_t p2 = fP[3]*fP[3] + fP[4]*fP[4] + fP[5]*fP[5]; 
  Double_t e0 = sqrt(m2+p2);

  Double_t mH[8];
  mH[0] = mH[1] = mH[2] = 0.;
  mH[3] = -2*fP[3]; 
  mH[4] = -2*fP[4]; 
  mH[5] = -2*fP[5]; 
  mH[6] =  2*fP[6];//e0;
  mH[7] = 0; 

  Double_t zeta = e0*e0 - e0*fP[6];
  zeta = m2 - (fP[6]*fP[6]-p2);
  
  Double_t mCHt[8], s2_est=0;
  for( Int_t i=0; i<8; ++i ){
    mCHt[i] = 0.0;
    for (Int_t j=0;j<8;++j) mCHt[i] += Cij(i,j)*mH[j];
    s2_est += mH[i]*mCHt[i];
  }
  
  if( s2_est<1.e-20 ) return; // calculated mass error is already 0, 
                              // the particle can not be constrained on mass

  Double_t w2 = 1./( s2 + s2_est );
  fChi2 += zeta*zeta*w2;
  fNDF  += 1;
  for( Int_t i=0, ii=0; i<8; ++i ){
    Double_t ki = mCHt[i]*w2;
    fP[i]+= ki*zeta;
    for(Int_t j=0;j<=i;++j) fC[ii++] -= ki*mCHt[j];    
  }
}


void KFParticleBase::SetNoDecayLength()
{  
  //* Set no decay length for resonances

  TransportToDecayVertex();

  Double_t h[8];
  h[0] = h[1] = h[2] = h[3] = h[4] = h[5] = h[6] = 0;
  h[7] = 1; 

  Double_t zeta = 0 - fP[7];
  for(Int_t i=0;i<8;++i) zeta -= h[i]*(fP[i]-fP[i]);
  
  Double_t s = fC[35];   
  if( s>1.e-20 ){
    s = 1./s;
    fChi2 += zeta*zeta*s;
    fNDF  += 1;
    for( Int_t i=0, ii=0; i<7; ++i ){
      Double_t ki = fC[28+i]*s;
      fP[i]+= ki*zeta;
      for(Int_t j=0;j<=i;++j) fC[ii++] -= ki*fC[28+j];    
    }
  }
  fP[7] = 0;
  fC[28] = fC[29] = fC[30] = fC[31] = fC[32] = fC[33] = fC[34] = fC[35] = 0;
}


void KFParticleBase::Construct( const KFParticleBase* vDaughters[], Int_t nDaughters,
                                   const KFParticleBase *Parent,  Double_t Mass, Bool_t IsConstrained         )
{ 
  //* Full reconstruction in one go

  Int_t maxIter = 1;
  bool wasLinearized = fIsLinearized;
  if( !fIsLinearized || IsConstrained ){
    //fVtxGuess[0] = fVtxGuess[1] = fVtxGuess[2] = 0;  //!!!!
    Double_t ds=0., ds1=0.;
    Double_t P[8], C[36];
    vDaughters[0]->GetDStoParticle(*vDaughters[1], ds, ds1);
    vDaughters[0]->Transport(ds,P,C);
    fVtxGuess[0] = P[0];
    fVtxGuess[1] = P[1];
    fVtxGuess[2] = P[2];
/*    fVtxGuess[0] = GetX();
    fVtxGuess[1] = GetY();
    fVtxGuess[2] = GetZ();*/

    fIsLinearized = 1;
    maxIter = 3;
  }

  Double_t constraintC[6];

  if( IsConstrained ){
    for(Int_t i=0;i<6;++i) constraintC[i]=fC[i];
  } else {
    for(Int_t i=0;i<6;++i) constraintC[i]=0.;
//    constraintC[0] = constraintC[2] = constraintC[5] = 100.;
    constraintC[0] = 100.*vDaughters[0]->fC[0];
    constraintC[2] = 100.*vDaughters[0]->fC[2];
    constraintC[5] = 100.*vDaughters[0]->fC[5];
  }


  for( Int_t iter=0; iter<maxIter; iter++ ){
    fAtProductionVertex = 0;
    fSFromDecay = 0;
    fP[0] = fVtxGuess[0];
    fP[1] = fVtxGuess[1];
    fP[2] = fVtxGuess[2];
    fP[3] = 0;
    fP[4] = 0;
    fP[5] = 0;
    fP[6] = 0;
    fP[7] = 0;
    SumDaughterMass = 0;

    for(Int_t i=0;i<6; ++i) fC[i]=constraintC[i];
    for(Int_t i=6;i<36;++i) fC[i]=0.;
    fC[35] = 1.;
    
    fNDF  = IsConstrained ?0 :-3;
    fChi2 =  0.;
    fQ = 0;

    for( Int_t itr =0; itr<nDaughters; itr++ ){
      AddDaughter( *vDaughters[itr] );    
    }
    if( iter<maxIter-1){
      for( Int_t i=0; i<3; i++ ) fVtxGuess[i] = fP[i];  
    }
  }
  fIsLinearized = wasLinearized;    

  if( Mass>=0 ) SetMassConstraint( Mass );
  if( Parent ) SetProductionVertex( *Parent );
}


void KFParticleBase::Convert( bool ToProduction )
{
  //* Tricky function - convert the particle error along its trajectory to 
  //* the value which corresponds to its production/decay vertex
  //* It is done by combination of the error of decay length with the position errors

  Double_t fld[3];
  {
    GetFieldValue( fP, fld );
    const Double_t kCLight =  fQ*0.000299792458;
    fld[0]*=kCLight; fld[1]*=kCLight; fld[2]*=kCLight;
  }

  Double_t h[6];
  
  h[0] = fP[3];
  h[1] = fP[4];
  h[2] = fP[5];
  if( ToProduction ){ h[0]=-h[0]; h[1]=-h[1]; h[2]=-h[2]; } 
  h[3] = h[1]*fld[2]-h[2]*fld[1];
  h[4] = h[2]*fld[0]-h[0]*fld[2];
  h[5] = h[0]*fld[1]-h[1]*fld[0];
  
  Double_t c;

  c = fC[28]+h[0]*fC[35];
  fC[ 0]+= h[0]*(c+fC[28]);
  fC[28] = c;

  fC[ 1]+= h[1]*fC[28] + h[0]*fC[29];
  c = fC[29]+h[1]*fC[35];
  fC[ 2]+= h[1]*(c+fC[29]);
  fC[29] = c;

  fC[ 3]+= h[2]*fC[28] + h[0]*fC[30];
  fC[ 4]+= h[2]*fC[29] + h[1]*fC[30];
  c = fC[30]+h[2]*fC[35];
  fC[ 5]+= h[2]*(c+fC[30]);
  fC[30] = c;

  fC[ 6]+= h[3]*fC[28] + h[0]*fC[31];
  fC[ 7]+= h[3]*fC[29] + h[1]*fC[31];
  fC[ 8]+= h[3]*fC[30] + h[2]*fC[31];
  c = fC[31]+h[3]*fC[35];
  fC[ 9]+= h[3]*(c+fC[31]);
  fC[31] = c;
  
  fC[10]+= h[4]*fC[28] + h[0]*fC[32];
  fC[11]+= h[4]*fC[29] + h[1]*fC[32];
  fC[12]+= h[4]*fC[30] + h[2]*fC[32];
  fC[13]+= h[4]*fC[31] + h[3]*fC[32];
  c = fC[32]+h[4]*fC[35];
  fC[14]+= h[4]*(c+fC[32]);
  fC[32] = c;
  
  fC[15]+= h[5]*fC[28] + h[0]*fC[33];
  fC[16]+= h[5]*fC[29] + h[1]*fC[33];
  fC[17]+= h[5]*fC[30] + h[2]*fC[33];
  fC[18]+= h[5]*fC[31] + h[3]*fC[33];
  fC[19]+= h[5]*fC[32] + h[4]*fC[33];
  c = fC[33]+h[5]*fC[35];
  fC[20]+= h[5]*(c+fC[33]);
  fC[33] = c;

  fC[21]+= h[0]*fC[34];
  fC[22]+= h[1]*fC[34];
  fC[23]+= h[2]*fC[34];
  fC[24]+= h[3]*fC[34];
  fC[25]+= h[4]*fC[34];
  fC[26]+= h[5]*fC[34];
}


void KFParticleBase::TransportToDecayVertex()
{
  //* Transport the particle to its decay vertex 

  if( fSFromDecay != 0 ) TransportToDS( -fSFromDecay );
  if( fAtProductionVertex ) Convert(0);
  fAtProductionVertex = 0;
}

void KFParticleBase::TransportToProductionVertex()
{
  //* Transport the particle to its production vertex 
  
  if( fSFromDecay != -fP[7] ) TransportToDS( -fSFromDecay-fP[7] );
  if( !fAtProductionVertex ) Convert( 1 );
  fAtProductionVertex = 1;
}


void KFParticleBase::TransportToDS( Double_t dS )
{ 
  //* Transport the particle on dS parameter (SignedPath/Momentum) 
 
  Transport( dS, fP, fC );
  fSFromDecay+= dS;
}


Double_t KFParticleBase::GetDStoPointLine( const Double_t xyz[] ) const 
{
  //* Get dS to a certain space point without field

  Double_t p2 = fP[3]*fP[3] + fP[4]*fP[4] + fP[5]*fP[5];  
  if( p2<1.e-4 ) p2 = 1;
  return ( fP[3]*(xyz[0]-fP[0]) + fP[4]*(xyz[1]-fP[1]) + fP[5]*(xyz[2]-fP[2]) )/p2;
}


Double_t KFParticleBase::GetDStoPointBz( Double_t B, const Double_t xyz[] ) 
  const
{ 
  
  //* Get dS to a certain space point for Bz field
  const Double_t kCLight = 0.000299792458;
  Double_t bq = B*fQ*kCLight;
  Double_t pt2 = fP[3]*fP[3] + fP[4]*fP[4];
  if( pt2<1.e-4 ) return 0;
  Double_t dx = xyz[0] - fP[0];
  Double_t dy = xyz[1] - fP[1]; 
  Double_t a = dx*fP[3]+dy*fP[4];
  Double_t dS;

  if( fabs(bq)<1.e-8 ) dS = a/pt2;  
  else dS =  atan2( bq*a, pt2 + bq*(dy*fP[3] -dx*fP[4]) )/bq;

  if(0){

    Double_t px = fP[3];
    Double_t py = fP[4];
    Double_t pz = fP[5];
    Double_t ss[2], g[2][5];
  
    ss[0] = dS;
    ss[1] = -dS;
    for( Int_t i=0; i<2; i++){
      Double_t bs = bq*ss[i];
      Double_t c = cos(bs), s = sin(bs);
      Double_t cB,sB;
      if( fabs(bq)>1.e-8){
        cB= (1-c)/bq;     
        sB= s/bq;  
      }else{
        const Double_t kOvSqr6 = 1./sqrt(6.);
        sB = (1.-bs*kOvSqr6)*(1.+bs*kOvSqr6)*ss[i];
        cB = .5*sB*bs;
      }
      g[i][0] = fP[0] + sB*px + cB*py;
      g[i][1] = fP[1] - cB*px + sB*py;
      g[i][2] = fP[2] + ss[i]*pz;
      g[i][3] =       + c*px + s*py;
      g[i][4] =       - s*px + c*py;      
    }

    Int_t i=0;
  
    Double_t dMin = 1.e10;
    for( Int_t j=0; j<2; j++){
      Double_t xx = g[j][0]-xyz[0];
      Double_t yy = g[j][1]-xyz[1];
      Double_t zz = g[j][2]-xyz[2];
      Double_t d = xx*xx + yy*yy + zz*zz;
      if( d<dMin ){
        dMin = d;
        i = j;
      }
    }

    dS = ss[i];

    Double_t x= g[i][0], y= g[i][1], z= g[i][2], ppx= g[i][3], ppy= g[i][4];      
    Double_t ddx = x-xyz[0];
    Double_t ddy = y-xyz[1];
    Double_t ddz = z-xyz[2];
    Double_t c = ddx*ppx  + ddy*ppy  + ddz*pz ;
    Double_t pp2 = ppx*ppx + ppy*ppy + pz*pz;    
    if( fabs(pp2)>1.e-8 ){
      dS+=c/pp2;
    }
  }
  return dS;
}

Double_t KFParticleBase::GetDStoPointBy( Double_t B, const Double_t xyz[] ) 
  const
{ 
  
  //* Get dS to a certain space point for Bz field
  const Double_t kCLight = 0.000299792458;
  Double_t bq = B*fQ*kCLight;
  Double_t pt2 = fP[3]*fP[3] + fP[5]*fP[5];
  if( pt2<1.e-4 ) return 0;
  Double_t dx = xyz[0] - fP[0];
  Double_t dy = -xyz[2] + fP[2]; 
  Double_t a = dx*fP[3]-dy*fP[5];
  Double_t dS;

  if( fabs(bq)<1.e-8 ) dS = a/pt2;  
  else dS =  atan2( bq*a, pt2 + bq*(dy*fP[3] +dx*fP[5]) )/bq;

  return dS;
}

void KFParticleBase::GetDStoParticleBz( Double_t B, const KFParticleBase &p, 
                                           Double_t &DS, Double_t &DS1 ) 
  const
{ 
  //* Get dS to another particle for Bz field
  Double_t px = fP[3];
  Double_t py = fP[4];
  Double_t pz = fP[5];

  Double_t px1 = p.fP[3];
  Double_t py1 = p.fP[4];
  Double_t pz1 = p.fP[5];

  const Double_t kCLight = 0.000299792458;

  Double_t bq = B*fQ*kCLight;
  Double_t bq1 = B*p.fQ*kCLight;
  Double_t s=0, ds=0, s1=0, ds1=0;

  if( fabs(bq)>1.e-8 || fabs(bq1)>1.e-8 ){

    Double_t dx = (p.fP[0] - fP[0]);
    Double_t dy = (p.fP[1] - fP[1]);
    Double_t d2 = (dx*dx+dy*dy);

    Double_t p2  = (px *px  + py *py); 
    Double_t p21 = (px1*px1 + py1*py1);

    if( fabs(p2) < 1.e-8 || fabs(p21) < 1.e-8 )
    {
      DS=0.;
      DS1=0.;
      return;
    }

    Double_t a = (px*py1 - py*px1);
    Double_t b = (px*px1 + py*py1);

    Double_t ldx = bq*bq1*dx - bq1*py + bq*py1 ;
    Double_t ldy = bq*bq1*dy + bq1*px - bq*px1 ;
    Double_t l2 = ldx*ldx + ldy*ldy;
    
    Double_t cS = bq1*p2 + bq*bq1*(dy* px - dx* py) -  bq*b;
    Double_t cS1= bq*p21 - bq*bq1*(dy*px1 - dx*py1) - bq1*b;

    Double_t ca  = bq*bq*bq1*d2  +2*( cS + bq*bq*(py1*dx-px1*dy)) ;
    Double_t ca1 = bq*bq1*bq1*d2 +2*( cS1 - bq1*bq1*(py*dx-px*dy)) ;  

    Double_t sa = 4*l2*p2 - ca*ca;
    Double_t sa1 = 4*l2*p21 - ca1*ca1;

    if(sa<0) sa=0;
    if(sa1<0)sa1=0;

    if( fabs(bq)>1.e-8){
      s  = atan2(   bq*( bq1*(dx*px +dy*py) + a ) , cS )/bq;
      ds = atan2(sqrt(sa),ca)/bq;
    } else {
      s = ( (dx*px + dy*py) + (py*px1-px*py1)/bq1)/p2;
      ds = s*s - (d2-2*(px1*dy-py1*dx)/bq1)/p2; 
      if( ds<0 ) ds = 0;
      ds = sqrt(ds);   
    }

    if( fabs(bq1)>1.e-8){
      s1 = atan2( -bq1*( bq*(dx*px1+dy*py1) + a), cS1 )/bq1;
      ds1 = atan2(sqrt(sa1),ca1)/bq1;  
    } else {
      s1 = (-(dx*px1 + dy*py1) + (py*px1-px*py1)/bq)/p21;
      ds1 = s1*s1 - (d2+2*(px*dy-py*dx)/bq)/p21; 
      if( ds1<0 ) ds1 = 0;
      ds1 = sqrt(ds1);
    }
  }
  Double_t ss[2], ss1[2], g[2][5],g1[2][5];
  
  ss[0] = s + ds;
  ss[1] = s - ds;
  ss1[0] = s1 + ds1;
  ss1[1] = s1 - ds1;

  for( Int_t i=0; i<2; i++){
    Double_t bs = bq*ss[i];
    Double_t c = cos(bs), sss = sin(bs);
    Double_t cB,sB;
    if( fabs(bq)>1.e-8){
      cB= (1-c)/bq;     
      sB= sss/bq;  
    }else{
      const Double_t kOvSqr6 = 1./sqrt(6.);
      sB = (1.-bs*kOvSqr6)*(1.+bs*kOvSqr6)*ss[i];
      cB = .5*sB*bs;
    }
    g[i][0] = fP[0] + sB*px + cB*py;
    g[i][1] = fP[1] - cB*px + sB*py;
    g[i][2] = fP[2] + ss[i]*pz;
    g[i][3] =       + c*px + sss*py;
    g[i][4] =       - sss*px + c*py;

    bs = bq1*ss1[i];  
    c =  cos(bs); sss = sin(bs);
    if( fabs(bq1)>1.e-8){
      cB= (1-c)/bq1;   
      sB= sss/bq1;  
    }else{
      const Double_t kOvSqr6 = 1./sqrt(6.);
      sB = (1.-bs*kOvSqr6)*(1.+bs*kOvSqr6)*ss1[i];
      cB = .5*sB*bs;
    }
      
    g1[i][0] = p.fP[0] + sB*px1 + cB*py1;
    g1[i][1] = p.fP[1] - cB*px1 + sB*py1;
    g1[i][2] = p.fP[2] + ss1[i]*pz1;
    g1[i][3] =         + c*px1 + sss*py1;
    g1[i][4] =         - sss*px1 + c*py1;
  }

  Int_t i=0, i1=0;
  
  Double_t dMin = 1.e10;
  for( Int_t j=0; j<2; j++){
    for( Int_t j1=0; j1<2; j1++){
      Double_t xx = g[j][0]-g1[j1][0];
      Double_t yy = g[j][1]-g1[j1][1];
      Double_t zz = g[j][2]-g1[j1][2];
      Double_t d = xx*xx + yy*yy + zz*zz;
      if( d<dMin ){
        dMin = d;
        i = j;
        i1 = j1;
      }
    }
  }  

  DS = ss[i];
  DS1 = ss1[i1];
  if(0){
    Double_t x= g[i][0], y= g[i][1], z= g[i][2], ppx= g[i][3], ppy= g[i][4];  
    Double_t x1=g1[i1][0], y1= g1[i1][1], z1= g1[i1][2], ppx1= g1[i1][3], ppy1= g1[i1][4];  
    Double_t dx = x1-x;
    Double_t dy = y1-y;
    Double_t dz = z1-z;
    Double_t a = ppx*ppx1 + ppy*ppy1 + pz*pz1;
    Double_t b = dx*ppx1 + dy*ppy1 + dz*pz1;
    Double_t c = dx*ppx  + dy*ppy  + dz*pz ;
    Double_t pp2 = ppx*ppx + ppy*ppy + pz*pz;
    Double_t pp21= ppx1*ppx1 + ppy1*ppy1 + pz1*pz1;
    Double_t det = pp2*pp21 - a*a;    
    if( fabs(det)>1.e-8 ){
      DS+=(a*b-pp21*c)/det;
      DS1+=(a*c-pp2*b)/det;
    }
  }
}

void KFParticleBase::GetDStoParticleBy( Double_t B, const KFParticleBase &p, 
                                        Double_t &DS, Double_t &DS1 ) const
{ 
  //* Get dS to another particle for Bz field
  Double_t px = fP[3];
  Double_t py = -fP[5];
  Double_t pz = fP[4];

  Double_t px1 = p.fP[3];
  Double_t py1 = -p.fP[5];
  Double_t pz1 = p.fP[4];

  const Double_t kCLight = 0.000299792458;

  Double_t bq = B*fQ*kCLight;
  Double_t bq1 = B*p.fQ*kCLight;
  Double_t s=0, ds=0, s1=0, ds1=0;

  if( fabs(bq)>1.e-8 || fabs(bq1)>1.e-8 ){

    Double_t dx = (p.fP[0] - fP[0]);
    Double_t dy = (-p.fP[2] + fP[2]);
    Double_t d2 = (dx*dx+dy*dy);

    Double_t p2  = (px *px  + py *py); 
    Double_t p21 = (px1*px1 + py1*py1);

    if( fabs(p2) < 1.e-8 || fabs(p21) < 1.e-8 )
    {
      DS=0.;
      DS1=0.;
      return;
    }

    Double_t a = (px*py1 - py*px1);
    Double_t b = (px*px1 + py*py1);

    Double_t ldx = bq*bq1*dx - bq1*py + bq*py1 ;
    Double_t ldy = bq*bq1*dy + bq1*px - bq*px1 ;
    Double_t l2 = ldx*ldx + ldy*ldy;
    
    Double_t cS = bq1*p2 + bq*bq1*(dy* px - dx* py) -  bq*b;
    Double_t cS1= bq*p21 - bq*bq1*(dy*px1 - dx*py1) - bq1*b;

    Double_t ca  = bq*bq*bq1*d2  +2*( cS + bq*bq*(py1*dx-px1*dy)) ;
    Double_t ca1 = bq*bq1*bq1*d2 +2*( cS1 - bq1*bq1*(py*dx-px*dy)) ;  

    Double_t sa = 4*l2*p2 - ca*ca;
    Double_t sa1 = 4*l2*p21 - ca1*ca1;

    if(sa<0) sa=0;
    if(sa1<0)sa1=0;

    if( fabs(bq)>1.e-8){
      s  = atan2(   bq*( bq1*(dx*px +dy*py) + a ) , cS )/bq;
      ds = atan2(sqrt(sa),ca)/bq;
    } else {
      s = ( (dx*px + dy*py) + (py*px1-px*py1)/bq1)/p2;
      ds = s*s - (d2-2*(px1*dy-py1*dx)/bq1)/p2; 
      if( ds<0 ) ds = 0;
      ds = sqrt(ds);   
    }

    if( fabs(bq1)>1.e-8){
      s1 = atan2( -bq1*( bq*(dx*px1+dy*py1) + a), cS1 )/bq1;
      ds1 = atan2(sqrt(sa1),ca1)/bq1;  
    } else {
      s1 = (-(dx*px1 + dy*py1) + (py*px1-px*py1)/bq)/p21;
      ds1 = s1*s1 - (d2+2*(px*dy-py*dx)/bq)/p21; 
      if( ds1<0 ) ds1 = 0;
      ds1 = sqrt(ds1);
    }
  }
  Double_t ss[2], ss1[2], g[2][5],g1[2][5];
  
  ss[0] = s + ds;
  ss[1] = s - ds;
  ss1[0] = s1 + ds1;
  ss1[1] = s1 - ds1;

  for( Int_t i=0; i<2; i++){
    Double_t bs = bq*ss[i];
    Double_t c = cos(bs), sss = sin(bs);
    Double_t cB,sB;
    if( fabs(bq)>1.e-8){
      cB= (1-c)/bq;     
      sB= sss/bq;  
    }else{
      const Double_t kOvSqr6 = 1./sqrt(6.);
      sB = (1.-bs*kOvSqr6)*(1.+bs*kOvSqr6)*ss[i];
      cB = .5*sB*bs;
    }
    g[i][0] = fP[0] + sB*px + cB*py;
    g[i][1] = -fP[2] - cB*px + sB*py;
    g[i][2] = fP[1] + ss[i]*pz;
    g[i][3] =       + c*px + sss*py;
    g[i][4] =       - sss*px + c*py;

    bs = bq1*ss1[i];  
    c =  cos(bs); sss = sin(bs);
    if( fabs(bq1)>1.e-8){
      cB= (1-c)/bq1;   
      sB= sss/bq1;  
    }else{
      const Double_t kOvSqr6 = 1./sqrt(6.);
      sB = (1.-bs*kOvSqr6)*(1.+bs*kOvSqr6)*ss1[i];
      cB = .5*sB*bs;
    }
      
    g1[i][0] = p.fP[0] + sB*px1 + cB*py1;
    g1[i][1] = -p.fP[2] - cB*px1 + sB*py1;
    g1[i][2] = p.fP[1] + ss1[i]*pz1;
    g1[i][3] =         + c*px1 + sss*py1;
    g1[i][4] =         - sss*px1 + c*py1;
  }

  Int_t i=0, i1=0;
  
  Double_t dMin = 1.e10;
  for( Int_t j=0; j<2; j++){
    for( Int_t j1=0; j1<2; j1++){
      Double_t xx = g[j][0]-g1[j1][0];
      Double_t yy = g[j][1]-g1[j1][1];
      Double_t zz = g[j][2]-g1[j1][2];
      Double_t d = xx*xx + yy*yy + zz*zz;
      if( d<dMin ){
        dMin = d;
        i = j;
        i1 = j1;
      }
    }
  }  

  DS = ss[i];
  DS1 = ss1[i1];
}

void KFParticleBase::GetDSIter(const KFParticleBase &p, Double_t const &dS, Double_t x[3], Double_t dx[3], Double_t ddx[3]) const
{
  Double_t ssx=0, ssy=0, ssz=0, ssyy=0, ssyz=0, ssyyy=0;
  Double_t dssx=0, dssy=0, dssz=0, dssyy=0, dssyz=0, dssyyy=0; // d(...)/dS
  Double_t ddssx=0, ddssy=0, ddssz=0, ddssyy=0, ddssyz=0, ddssyyy=0; // d2(...)/dS2
  Double_t Kssx=0, Kssy=0, Kssz=0, Kssyy=0, Kssyz=0, Kssyyy=0;

  const Double_t kCLight = 0.000299792458;
  Double_t c = fQ*kCLight;

  // get field integrals

  Double_t fld[3][3];   
  Double_t p0[3], p1[3], p2[3];

  // line track approximation

  p0[0] = p.fP[0];
  p0[1] = p.fP[1];
  p0[2] = p.fP[2];

  p2[0] = p.fP[0] + p.fP[3]*dS;
  p2[1] = p.fP[1] + p.fP[4]*dS;
  p2[2] = p.fP[2] + p.fP[5]*dS;

  p1[0] = 0.5*(p0[0]+p2[0]);
  p1[1] = 0.5*(p0[1]+p2[1]);
  p1[2] = 0.5*(p0[2]+p2[2]);

  // first order track approximation
  {
    GetFieldValue( p0, fld[0] );
    GetFieldValue( p1, fld[1] );
    GetFieldValue( p2, fld[2] );

    Double_t ssy1 = ( 7*fld[0][1] + 6*fld[1][1]-fld[2][1] )*c*dS*dS/96.;
    Double_t ssy2 = (   fld[0][1] + 2*fld[1][1]         )*c*dS*dS/6.;

    p1[0] -= ssy1*p.fP[5];
    p1[2] += ssy1*p.fP[3];
    p2[0] -= ssy2*p.fP[5];
    p2[2] += ssy2*p.fP[3];
  }

  GetFieldValue( p0, fld[0] );
  GetFieldValue( p1, fld[1] );
  GetFieldValue( p2, fld[2] );

  Kssx = c*( fld[0][0] + 2*fld[1][0]) / 6.;
  Kssy = c*( fld[0][1] + 2*fld[1][1]) / 6.;
  Kssz = c*( fld[0][2] + 2*fld[1][2]) / 6.;

//  Double_t c2[3][3]    =   { {  5, -4, -1},{  44,  80,  -4},{ 11, 44, 5} }; // /=360.    
  Double_t cc2[3][3]    =   { { 38,  8, -4},{ 148, 208, -20},{  3, 36, 3} }; // /=2520.
  for(Int_t n=0; n<3; n++)
    for(Int_t m=0; m<3; m++) 
    {
      Kssyz += cc2[n][m]*fld[n][1]*fld[m][2];
    }
  Kssyz *= c*c / 2520.;

  Kssyy = ( fld[0][1]*( 38*fld[0][1] + 156*fld[1][1]  -   fld[2][1] )+
            fld[1][1]*(              208*fld[1][1]  +16*fld[2][1] )+
            fld[2][1]*(                             3*fld[2][1] )  
          )*c*c/2520.;
  Kssyyy = ( fld[0][1]*( fld[0][1]*( 85*fld[0][1] + 526*fld[1][1]  - 7*fld[2][1] )+
             fld[1][1]*(             1376*fld[1][1]  +84*fld[2][1] )+
             fld[2][1]*(                            19*fld[2][1] )  )+
             fld[1][1]*( fld[1][1]*(             1376*fld[1][1] +256*fld[2][1] )+
             fld[2][1]*(                            62*fld[2][1] )  )+
             fld[2][1]*fld[2][1]  *(                             3*fld[2][1] )
           )*c*c*c/90720.;

  ssx = Kssx * dS*dS;
  ssy = Kssy * dS*dS;
  ssz = Kssz * dS*dS;
  ssyz = Kssyz * dS*dS*dS;
  ssyy = Kssyy * dS*dS*dS;
  ssyyy = Kssyyy * dS*dS*dS*dS;

  dssx = 2.*Kssx * dS;
  dssy = 2.*Kssy * dS;
  dssz = 2.*Kssz * dS;
  dssyz = 3.*Kssyz * dS*dS;
  dssyy = 3.*Kssyy * dS*dS;
  dssyyy = 4.*Kssyyy * dS*dS*dS;

  ddssx = 2.*Kssx;
  ddssy = 2.*Kssy;
  ddssz = 2.*Kssz;
  ddssyz = 2.*3.*Kssyz * dS;
  ddssyy = 2.*3.*Kssyy * dS;
  ddssyyy = 3.*4.*Kssyyy * dS*dS;

  Double_t mJ[3][3];
  for( Int_t iJ=0; iJ<3; iJ++ ) for( Int_t jJ=0; jJ<3; jJ++) mJ[iJ][jJ]=0;

  mJ[0][0]=dS-ssyy;   mJ[0][1]=ssx;  mJ[0][2]=ssyyy-ssy;
  mJ[1][0]=-ssz;      mJ[1][1]=dS;   mJ[1][2]=ssx+ssyz;
  mJ[2][0]=ssy-ssyyy; mJ[2][1]=-ssx; mJ[2][2]=dS-ssyy;

  x[0] = p.fP[0] + mJ[0][0]*p.fP[3] + mJ[0][1]*p.fP[4] + mJ[0][2]*p.fP[5];
  x[1] = p.fP[1] + mJ[1][0]*p.fP[3] + mJ[1][1]*p.fP[4] + mJ[1][2]*p.fP[5];
  x[2] = p.fP[2] + mJ[2][0]*p.fP[3] + mJ[2][1]*p.fP[4] + mJ[2][2]*p.fP[5];

  mJ[0][0]= 1-dssyy;      mJ[0][1]= dssx;  mJ[0][2]= dssyyy-dssy;
  mJ[1][0]= -dssz;        mJ[1][1]= 1;     mJ[1][2]= dssx+dssyz;
  mJ[2][0]= dssy-dssyyy;  mJ[2][1]= -dssx; mJ[2][2]= 1-dssyy;

  dx[0] = p.fP[0] + mJ[0][0]*p.fP[3] + mJ[0][1]*p.fP[4] + mJ[0][2]*p.fP[5];
  dx[1] = p.fP[1] + mJ[1][0]*p.fP[3] + mJ[1][1]*p.fP[4] + mJ[1][2]*p.fP[5];
  dx[2] = p.fP[2] + mJ[2][0]*p.fP[3] + mJ[2][1]*p.fP[4] + mJ[2][2]*p.fP[5];

  mJ[0][0]= -ddssyy;        mJ[0][1]= ddssx;  mJ[0][2]= ddssyyy-ddssy;
  mJ[1][0]= -ddssz;         mJ[1][1]= 0;      mJ[1][2]= ddssx+ddssyz;
  mJ[2][0]= ddssy-ddssyyy;  mJ[2][1]= -ddssx; mJ[2][2]= -ddssyy;

  ddx[0] = p.fP[0] + mJ[0][0]*p.fP[3] + mJ[0][1]*p.fP[4] + mJ[0][2]*p.fP[5];
  ddx[1] = p.fP[1] + mJ[1][0]*p.fP[3] + mJ[1][1]*p.fP[4] + mJ[1][2]*p.fP[5];
  ddx[2] = p.fP[2] + mJ[2][0]*p.fP[3] + mJ[2][1]*p.fP[4] + mJ[2][2]*p.fP[5];
}

Double_t KFParticleBase::GetDStoPointCBM( const Double_t xyz[] ) const
{
  //* Transport the particle on dS, output to P[],C[], for CBM field

  Double_t dS = 0;
  //Linear approximation

  Double_t fld[3];
  GetFieldValue( fP, fld );
// 
//   GetDStoParticleBy(fld[1],p,dS,dS1);
  dS = GetDStoPointLine( xyz );

  if( fQ==0 ){
    return dS;
  }

  dS = GetDStoPointBy( fld[1],xyz );

//  const Double_t &px   = fP[3], &py   = fP[4], &pz   = fP[5];


  // construct coefficients 
// int NIt;
//   for(int i=0; i<100; i++)
//   {
// //std::cout << "  dS temp "<<dS << std::endl;
//     Double_t x[3], dx[3], ddx[3];
// 
//     GetDSIter(*this, dS, x, dx, ddx);
// 
//     Double_t dr[3] = { x[0] - xyz[0], x[1] - xyz[1], x[2] - xyz[2] };
// 
//     Double_t dS0 = dS;
// 
//     Double_t f  = dx[0] * dr[0] + dx[1] * dr[1] + dx[2] * dr[2];
//     Double_t df  = ddx[0] * dr[0] + ddx[1] * dr[1] + ddx[2] * dr[2] + dx[0]*dx[0] + dx[1]*dx[1] + dx[2]*dx[2];
// 
//     dS = dS - f/df;
//     NIt++;
//     if(fabs(dS - dS0) < fabs(dS)*0.001) break;
//   }
//std::cout << "NIt  " << NIt <<"  dS  "<<  dS << std::endl;
  return dS;
}

void KFParticleBase::GetDStoParticleLine( const KFParticleBase &p, Double_t &dS, Double_t &dS1 ) const
{
  Double_t p12 = fP[3]*fP[3] + fP[4]*fP[4] + fP[5]*fP[5];
  Double_t p22 = p.fP[3]*p.fP[3] + p.fP[4]*p.fP[4] + p.fP[5]*p.fP[5];
  Double_t p1p2 = fP[3]*p.fP[3] + fP[4]*p.fP[4] + fP[5]*p.fP[5];

  Double_t drp1 = fP[3]*(p.fP[0]-fP[0]) + fP[4]*(p.fP[1]-fP[1]) + fP[5]*(p.fP[2]-fP[2]);
  Double_t drp2 = p.fP[3]*(p.fP[0]-fP[0]) + p.fP[4]*(p.fP[1]-fP[1]) + p.fP[5]*(p.fP[2]-fP[2]);

  Double_t detp =  p1p2*p1p2 - p12*p22;
  if( fabs(detp)<1.e-4 ) detp = 1; //TODO correct!!!

  dS  = (drp2*p1p2 - drp1*p22) /detp;
  dS1 = (drp2*p12  - drp1*p1p2)/detp;
}

void KFParticleBase::GetDStoParticleCBM( const KFParticleBase &p, Double_t &dS, Double_t &dS1 ) const
{
  //* Transport the particle on dS, output to P[],C[], for CBM field

  GetDStoParticleLine( p, dS, dS1 );
  if( fQ==0 ){
    return;
  }

  Double_t fld[3];
  GetFieldValue( fP, fld );

  Double_t fld1[3];
  GetFieldValue( p.fP, fld1 );


  GetDStoParticleBy((fld[1]+fld1[1])/2,p,dS,dS1);

//   construct coefficients 
// int NIt;
//   for(int i=0; i<10; i++)
//   {
// /*std::cout << "  dS temp "<<dS <<  "  dS1 temp "<< dS1 << std::endl;*/
//     Double_t x[3],  dx[3],  ddx[3];
//     Double_t x1[3], dx1[3], ddx1[3];
// 
//     GetDSIter(*this, dS, x, dx, ddx);
//     GetDSIter(p, dS1, x1, dx1, ddx1);
// 
//     Double_t dr[3] = { x[0] - x1[0], x[1] - x1[1], x[2] - x1[2] };
// 
//     Double_t dS0 = dS;
//     Double_t dS10 = dS1;
// 
//     Double_t f    = dx[0]  * dr[0] + dx[1]  * dr[1] + dx[2]  * dr[2];
//     Double_t dfs  = ddx[0] * dr[0] + ddx[1] * dr[1] + ddx[2] * dr[2] + dx[0]*dx[0] + dx[1]*dx[1] + dx[2]*dx[2];
//     Double_t dfs1 = -ddx[0] * ddx1[0] - ddx[1] * ddx1[1] - ddx[2] * ddx1[2];
// 
//     Double_t f1    = dx1[0]  * dr[0] + dx1[1]  * dr[1] + dx1[2]  * dr[2];
//     Double_t df1s1 = ddx1[0] * dr[0] + ddx1[1] * dr[1] + ddx1[2] * dr[2] - dx1[0]*dx1[0] - dx1[1]*dx1[1] - dx1[2]*dx1[2];
//     Double_t df1s  = -dfs1;
// 
//     Double_t det = dfs*df1s1 - dfs1*df1s;
//     if(fabs(det) < 1.e-8) det = 1.e-8;
// 
//     Double_t DS  = dfs1*f1 - f*df1s1;
//     Double_t DS1 = f*df1s - f1*dfs;
// 
//     dS  += DS/det;
//     dS1 += DS1/det;
//     NIt++;
// /*    if( (fabs(dS - dS0) < fabs(dS)*0.001) && (fabs(dS1 - dS10) < fabs(dS1)*0.001)) break;*/
//   }
//std::cout << "NIt  " << NIt <<"  dS  "<<  dS << "  dS1  "<<  dS1 << std::endl;
}

void KFParticleBase::TransportCBM( Double_t dS, 
                                 Double_t P[], Double_t C[] ) const
{  
  //* Transport the particle on dS, output to P[],C[], for CBM field
 
  if( fQ==0 ){
    TransportLine( dS, P, C );
    return;
  }

  const Double_t kCLight = 0.000299792458;

  Double_t c = fQ*kCLight;

  // construct coefficients 

  Double_t 
    px   = fP[3],
    py   = fP[4],
    pz   = fP[5];
      
  Double_t sx=0, sy=0, sz=0, syy=0, syz=0, syyy=0, ssx=0, ssy=0, ssz=0, ssyy=0, ssyz=0, ssyyy=0;

  { // get field integrals

    Double_t fld[3][3];   
    Double_t p0[3], p1[3], p2[3];

    // line track approximation

    p0[0] = fP[0];
    p0[1] = fP[1];
    p0[2] = fP[2];
  
    p2[0] = fP[0] + px*dS;
    p2[1] = fP[1] + py*dS;
    p2[2] = fP[2] + pz*dS;
  
    p1[0] = 0.5*(p0[0]+p2[0]);
    p1[1] = 0.5*(p0[1]+p2[1]);
    p1[2] = 0.5*(p0[2]+p2[2]);

    // first order track approximation
    {
      GetFieldValue( p0, fld[0] );
      GetFieldValue( p1, fld[1] );
      GetFieldValue( p2, fld[2] );

      Double_t ssy1 = ( 7*fld[0][1] + 6*fld[1][1]-fld[2][1] )*c*dS*dS/96.;
      Double_t ssy2 = (   fld[0][1] + 2*fld[1][1]         )*c*dS*dS/6.;

      p1[0] -= ssy1*pz;
      p1[2] += ssy1*px;
      p2[0] -= ssy2*pz;
      p2[2] += ssy2*px;   
    }

    GetFieldValue( p0, fld[0] );
    GetFieldValue( p1, fld[1] );
    GetFieldValue( p2, fld[2] );
    
    sx = c*( fld[0][0] + 4*fld[1][0] + fld[2][0] )*dS/6.;
    sy = c*( fld[0][1] + 4*fld[1][1] + fld[2][1] )*dS/6.;
    sz = c*( fld[0][2] + 4*fld[1][2] + fld[2][2] )*dS/6.;

    ssx = c*( fld[0][0] + 2*fld[1][0])*dS*dS/6.;
    ssy = c*( fld[0][1] + 2*fld[1][1])*dS*dS/6.;
    ssz = c*( fld[0][2] + 2*fld[1][2])*dS*dS/6.;

    Double_t c2[3][3]    =   { {  5, -4, -1},{  44,  80,  -4},{ 11, 44, 5} }; // /=360.    
    Double_t cc2[3][3]    =   { { 38,  8, -4},{ 148, 208, -20},{  3, 36, 3} }; // /=2520.
    for(Int_t n=0; n<3; n++)
      for(Int_t m=0; m<3; m++) 
        {
          syz += c2[n][m]*fld[n][1]*fld[m][2];
          ssyz += cc2[n][m]*fld[n][1]*fld[m][2];
        }
 
    syz  *= c*c*dS*dS/360.;
    ssyz  *= c*c*dS*dS*dS/2520.;
    
    syy  = c*( fld[0][1] + 4*fld[1][1] + fld[2][1] )*dS;
    syyy = syy*syy*syy / 1296;
    syy  = syy*syy/72;

    ssyy = ( fld[0][1]*( 38*fld[0][1] + 156*fld[1][1]  -   fld[2][1] )+
            fld[1][1]*(              208*fld[1][1]  +16*fld[2][1] )+
            fld[2][1]*(                             3*fld[2][1] )  
            )*dS*dS*dS*c*c/2520.;
    ssyyy = 
      (
       fld[0][1]*( fld[0][1]*( 85*fld[0][1] + 526*fld[1][1]  - 7*fld[2][1] )+
                 fld[1][1]*(             1376*fld[1][1]  +84*fld[2][1] )+
                 fld[2][1]*(                            19*fld[2][1] )  )+
       fld[1][1]*( fld[1][1]*(             1376*fld[1][1] +256*fld[2][1] )+
                 fld[2][1]*(                            62*fld[2][1] )  )+
       fld[2][1]*fld[2][1]  *(                             3*fld[2][1] )       
       )*dS*dS*dS*dS*c*c*c/90720.;    
 
  }

  Double_t mJ[8][8];
  for( Int_t i=0; i<8; i++ ) for( Int_t j=0; j<8; j++) mJ[i][j]=0;

  mJ[0][0]=1; mJ[0][1]=0; mJ[0][2]=0; mJ[0][3]=dS-ssyy;  mJ[0][4]=ssx;  mJ[0][5]=ssyyy-ssy;
  mJ[1][0]=0; mJ[1][1]=1; mJ[1][2]=0; mJ[1][3]=-ssz;     mJ[1][4]=dS;  mJ[1][5]=ssx+ssyz;
  mJ[2][0]=0; mJ[2][1]=0; mJ[2][2]=1; mJ[2][3]=ssy-ssyyy; mJ[2][4]=-ssx; mJ[2][5]=dS-ssyy;
  
  mJ[3][0]=0; mJ[3][1]=0; mJ[3][2]=0; mJ[3][3]=1-syy;   mJ[3][4]=sx;  mJ[3][5]=syyy-sy;
  mJ[4][0]=0; mJ[4][1]=0; mJ[4][2]=0; mJ[4][3]=-sz;     mJ[4][4]=1;   mJ[4][5]=sx+syz;
  mJ[5][0]=0; mJ[5][1]=0; mJ[5][2]=0; mJ[5][3]=sy-syyy; mJ[5][4]=-sx; mJ[5][5]=1-syy;
  mJ[6][6] = mJ[7][7] = 1;
  
  P[0] = fP[0] + mJ[0][3]*px + mJ[0][4]*py + mJ[0][5]*pz;
  P[1] = fP[1] + mJ[1][3]*px + mJ[1][4]*py + mJ[1][5]*pz;
  P[2] = fP[2] + mJ[2][3]*px + mJ[2][4]*py + mJ[2][5]*pz;
  P[3] =        mJ[3][3]*px + mJ[3][4]*py + mJ[3][5]*pz;
  P[4] =        mJ[4][3]*px + mJ[4][4]*py + mJ[4][5]*pz;
  P[5] =        mJ[5][3]*px + mJ[5][4]*py + mJ[5][5]*pz;
  P[6] = fP[6];
  P[7] = fP[7];

  MultQSQt( mJ[0], fC, C);

}


void KFParticleBase::TransportBz( Double_t b, Double_t t,
                                     Double_t p[], Double_t e[] ) const 
{ 
  //* Transport the particle on dS, output to P[],C[], for Bz field
 
  const Double_t kCLight = 0.000299792458;
  b = b*fQ*kCLight;
  Double_t bs= b*t;
  Double_t s = sin(bs), c = cos(bs);
  Double_t sB, cB;
  if( fabs(bs)>1.e-10){
    sB= s/b;
    cB= (1-c)/b;
  }else{
    const Double_t kOvSqr6 = 1./sqrt(6.);
    sB = (1.-bs*kOvSqr6)*(1.+bs*kOvSqr6)*t;
    cB = .5*sB*bs;
  }
  
  Double_t px = fP[3];
  Double_t py = fP[4];
  Double_t pz = fP[5];

  p[0] = fP[0] + sB*px + cB*py;
  p[1] = fP[1] - cB*px + sB*py;
  p[2] = fP[2] +  t*pz;
  p[3] =          c*px + s*py;
  p[4] =         -s*px + c*py;
  p[5] = fP[5];
  p[6] = fP[6];
  p[7] = fP[7];

  /* 
  Double_t mJ[8][8] = { {1,0,0,   sB, cB,  0, 0, 0 },
                        {0,1,0,  -cB, sB,  0, 0, 0 },
                        {0,0,1,    0,  0,  t, 0, 0 },
                        {0,0,0,    c,  s,  0, 0, 0 },
                        {0,0,0,   -s,  c,  0, 0, 0 },
                        {0,0,0,    0,  0,  1, 0, 0 },
                        {0,0,0,    0,  0,  0, 1, 0 },
                        {0,0,0,    0,  0,  0, 0, 1 }  };
  Double_t mA[8][8];
  for( Int_t k=0,i=0; i<8; i++)
    for( Int_t j=0; j<=i; j++, k++ ) mA[i][j] = mA[j][i] = fC[k]; 

  Double_t mJC[8][8];
  for( Int_t i=0; i<8; i++ )
    for( Int_t j=0; j<8; j++ ){
      mJC[i][j]=0;
      for( Int_t k=0; k<8; k++ ) mJC[i][j]+=mJ[i][k]*mA[k][j];
    }
  
  for( Int_t k=0,i=0; i<8; i++)
    for( Int_t j=0; j<=i; j++, k++ ){
      e[k] = 0;
      for( Int_t l=0; l<8; l++ ) e[k]+=mJC[i][l]*mJ[j][l];
    }
  
  return;
  */

  Double_t 
    c6=fC[6], c7=fC[7], c8=fC[8], c17=fC[17], c18=fC[18],
    c24 = fC[24], c31 = fC[31];

  Double_t 
    cBC13 = cB*fC[13],
    mJC13 = c7 - cB*fC[9] + sB*fC[13],
    mJC14 = fC[11] - cBC13 + sB*fC[14],
    mJC23 = c8 + t*c18,
    mJC24 = fC[12] + t*fC[19],
    mJC33 = c*fC[9] + s*fC[13],
    mJC34 = c*fC[13] + s*fC[14],
    mJC43 = -s*fC[9] + c*fC[13],
    mJC44 = -s*fC[13] + c*fC[14];


  e[0]= fC[0] + 2*(sB*c6 + cB*fC[10]) + (sB*fC[9] + 2*cBC13)*sB + cB*cB*fC[14];
  e[1]= fC[1] - cB*c6 + sB*fC[10] + mJC13*sB + mJC14*cB;
  e[2]= fC[2] - cB*c7 + sB*fC[11] - mJC13*cB + mJC14*sB;
  e[3]= fC[3] + t*fC[15] + mJC23*sB + mJC24*cB;
  e[4]= fC[4] + t*fC[16] - mJC23*cB + mJC24*sB;

  e[15]= fC[15] + c18*sB + fC[19]*cB;
  e[16]= fC[16] - c18*cB + fC[19]*sB;
  e[17]= c17 + fC[20]*t;
  e[18]= c18*c + fC[19]*s;
  e[19]= -c18*s + fC[19]*c;

  e[5]= fC[5] + (c17 + e[17] )*t;

  e[6]= c*c6 + s*fC[10] + mJC33*sB + mJC34*cB;
  e[7]= c*c7 + s*fC[11] - mJC33*cB + mJC34*sB;
  e[8]= c*c8 + s*fC[12] + e[18]*t;
  e[9]= mJC33*c + mJC34*s;
  e[10]= -s*c6 + c*fC[10] + mJC43*sB + mJC44*cB;

    
  e[11]= -s*c7 + c*fC[11] - mJC43*cB + mJC44*sB;
  e[12]= -s*c8 + c*fC[12] + e[19]*t;
  e[13]= mJC43*c + mJC44*s;
  e[14]= -mJC43*s + mJC44*c;
  e[20]= fC[20];
  e[21]= fC[21] + fC[25]*cB + c24*sB;
  e[22]= fC[22] - c24*cB + fC[25]*sB;
  e[23]= fC[23] + fC[26]*t;
  e[24]= c*c24 + s*fC[25];
  e[25]= c*fC[25] - c24*s;
  e[26]= fC[26];
  e[27]= fC[27];
  e[28]= fC[28] + fC[32]*cB + c31*sB;
  e[29]= fC[29] - c31*cB + fC[32]*sB;
  e[30]= fC[30] + fC[33]*t;
  e[31]= c*c31 + s*fC[32];
  e[32]= c*fC[32] - s*c31;
  e[33]= fC[33];
  e[34]= fC[34];
  e[35]= fC[35];     
}


Double_t KFParticleBase::GetDistanceFromVertex( const KFParticleBase &Vtx ) const
{
  //* Calculate distance from vertex [cm]

  return GetDistanceFromVertex( Vtx.fP );
}

Double_t KFParticleBase::GetDistanceFromVertex( const Double_t vtx[] ) const
{
  //* Calculate distance from vertex [cm]

  Double_t mP[8], mC[36];  
  Transport( GetDStoPoint(vtx), mP, mC );
  Double_t d[3]={ vtx[0]-mP[0], vtx[1]-mP[1], vtx[2]-mP[2]};
  return sqrt( d[0]*d[0]+d[1]*d[1]+d[2]*d[2] );
}

Double_t KFParticleBase::GetDistanceFromParticle( const KFParticleBase &p ) 
  const
{ 
  //* Calculate distance to other particle [cm]

  Double_t dS, dS1;
  GetDStoParticle( p, dS, dS1 );   
  Double_t mP[8], mC[36], mP1[8], mC1[36];
  Transport( dS, mP, mC ); 
  p.Transport( dS1, mP1, mC1 ); 
  Double_t dx = mP[0]-mP1[0]; 
  Double_t dy = mP[1]-mP1[1]; 
  Double_t dz = mP[2]-mP1[2]; 
  return sqrt(dx*dx+dy*dy+dz*dz);
}

Double_t KFParticleBase::GetDeviationFromVertex( const KFParticleBase &Vtx ) const
{
  //* Calculate sqrt(Chi2/ndf) deviation from vertex

  return GetDeviationFromVertex( Vtx.fP, Vtx.fC );
}


Double_t KFParticleBase::GetDeviationFromVertex( const Double_t v[], const Double_t Cv[] ) const
{
  //* Calculate sqrt(Chi2/ndf) deviation from vertex
  //* v = [xyz], Cv=[Cxx,Cxy,Cyy,Cxz,Cyz,Czz]-covariance matrix

  Double_t mP[8];
  Double_t mC[36];
  
  Transport( GetDStoPoint(v), mP, mC );  

  Double_t d[3]={ v[0]-mP[0], v[1]-mP[1], v[2]-mP[2]};

  Double_t sigmaS = .1+10.*sqrt( (d[0]*d[0]+d[1]*d[1]+d[2]*d[2])/
                                 (mP[3]*mP[3]+mP[4]*mP[4]+mP[5]*mP[5])  );

   
  Double_t h[3] = { mP[3]*sigmaS, mP[4]*sigmaS, mP[5]*sigmaS };       
  
  Double_t mSi[6] = 
    { mC[0] +h[0]*h[0], 
      mC[1] +h[1]*h[0], mC[2] +h[1]*h[1], 
      mC[3] +h[2]*h[0], mC[4] +h[2]*h[1], mC[5] +h[2]*h[2] };

  if( Cv ){
    mSi[0]+=Cv[0];
    mSi[1]+=Cv[1];
    mSi[2]+=Cv[2];
    mSi[3]+=Cv[3];
    mSi[4]+=Cv[4];
    mSi[5]+=Cv[5];
  }
  
  Double_t mS[6];

  mS[0] = mSi[2]*mSi[5] - mSi[4]*mSi[4];
  mS[1] = mSi[3]*mSi[4] - mSi[1]*mSi[5];
  mS[2] = mSi[0]*mSi[5] - mSi[3]*mSi[3];
  mS[3] = mSi[1]*mSi[4] - mSi[2]*mSi[3];
  mS[4] = mSi[1]*mSi[3] - mSi[0]*mSi[4];
  mS[5] = mSi[0]*mSi[2] - mSi[1]*mSi[1];         
      
  Double_t s = ( mSi[0]*mS[0] + mSi[1]*mS[1] + mSi[3]*mS[3] );
  s = ( s > 1.E-20 )  ?1./s :0;   

  return sqrt( fabs(s*( ( mS[0]*d[0] + mS[1]*d[1] + mS[3]*d[2])*d[0]
                   +(mS[1]*d[0] + mS[2]*d[1] + mS[4]*d[2])*d[1]
                   +(mS[3]*d[0] + mS[4]*d[1] + mS[5]*d[2])*d[2] ))/2);
}


Double_t KFParticleBase::GetDeviationFromParticle( const KFParticleBase &p ) 
  const
{ 
  //* Calculate sqrt(Chi2/ndf) deviation from other particle

  Double_t dS, dS1;
  GetDStoParticle( p, dS, dS1 );   
  Double_t mP1[8], mC1[36];
  p.Transport( dS1, mP1, mC1 ); 

  Double_t d[3]={ fP[0]-mP1[0], fP[1]-mP1[1], fP[2]-mP1[2]};

  Double_t sigmaS = .1+10.*sqrt( (d[0]*d[0]+d[1]*d[1]+d[2]*d[2])/
                                        (mP1[3]*mP1[3]+mP1[4]*mP1[4]+mP1[5]*mP1[5])  );

  Double_t h[3] = { mP1[3]*sigmaS, mP1[4]*sigmaS, mP1[5]*sigmaS };       
  
  mC1[0] +=h[0]*h[0];
  mC1[1] +=h[1]*h[0]; 
  mC1[2] +=h[1]*h[1]; 
  mC1[3] +=h[2]*h[0]; 
  mC1[4] +=h[2]*h[1];
  mC1[5] +=h[2]*h[2];

  return GetDeviationFromVertex( mP1, mC1 )*sqrt(2./1.);
}



void KFParticleBase::SubtractFromVertex(  KFParticleBase &Vtx ) const
{
  //* Subtract the particle from the vertex  

  Double_t fld[3];  
  {
    GetFieldValue( Vtx.fP, fld );
    const Double_t kCLight =  0.000299792458;
    fld[0]*=kCLight; fld[1]*=kCLight; fld[2]*=kCLight;
  }

  Double_t m[8];
  Double_t mCm[36];

  if( Vtx.fIsLinearized ){
    GetMeasurement( Vtx.fVtxGuess, m, mCm );
  } else {
    GetMeasurement( Vtx.fP, m, mCm );
  }

  Double_t mV[6];

  mV[ 0] = mCm[ 0];
  mV[ 1] = mCm[ 1];
  mV[ 2] = mCm[ 2];
  mV[ 3] = mCm[ 3];
  mV[ 4] = mCm[ 4];
  mV[ 5] = mCm[ 5];
     
  //* 
            
  Double_t mS[6];
  {
    Double_t mSi[6] = { mV[0]-Vtx.fC[0], 
                        mV[1]-Vtx.fC[1], mV[2]-Vtx.fC[2], 
                        mV[3]-Vtx.fC[3], mV[4]-Vtx.fC[4], mV[5]-Vtx.fC[5] };
    
    mS[0] = mSi[2]*mSi[5] - mSi[4]*mSi[4];
    mS[1] = mSi[3]*mSi[4] - mSi[1]*mSi[5];
    mS[2] = mSi[0]*mSi[5] - mSi[3]*mSi[3];
    mS[3] = mSi[1]*mSi[4] - mSi[2]*mSi[3];
    mS[4] = mSi[1]*mSi[3] - mSi[0]*mSi[4];
    mS[5] = mSi[0]*mSi[2] - mSi[1]*mSi[1];       
    
    Double_t s = ( mSi[0]*mS[0] + mSi[1]*mS[1] + mSi[3]*mS[3] );
    s = ( s > 1.E-20 )  ?1./s :0;         
    mS[0]*=s;
    mS[1]*=s;
    mS[2]*=s;
    mS[3]*=s;
    mS[4]*=s;
    mS[5]*=s;
  }
    
  //* Residual (measured - estimated)
    
  Double_t zeta[3] = { m[0]-Vtx.fP[0], m[1]-Vtx.fP[1], m[2]-Vtx.fP[2] };
        
  //* mCHt = mCH' - D'
    
  Double_t mCHt0[3], mCHt1[3], mCHt2[3];
    
  mCHt0[0]=Vtx.fC[ 0] ;      mCHt1[0]=Vtx.fC[ 1] ;      mCHt2[0]=Vtx.fC[ 3] ;
  mCHt0[1]=Vtx.fC[ 1] ;      mCHt1[1]=Vtx.fC[ 2] ;      mCHt2[1]=Vtx.fC[ 4] ;
  mCHt0[2]=Vtx.fC[ 3] ;      mCHt1[2]=Vtx.fC[ 4] ;      mCHt2[2]=Vtx.fC[ 5] ;
  
  //* Kalman gain K = mCH'*S
    
  Double_t k0[3], k1[3], k2[3];
    
  for(Int_t i=0;i<3;++i){
    k0[i] = mCHt0[i]*mS[0] + mCHt1[i]*mS[1] + mCHt2[i]*mS[3];
    k1[i] = mCHt0[i]*mS[1] + mCHt1[i]*mS[2] + mCHt2[i]*mS[4];
    k2[i] = mCHt0[i]*mS[3] + mCHt1[i]*mS[4] + mCHt2[i]*mS[5];
  }
    
  //* New estimation of the vertex position r += K*zeta
    
  Double_t dChi2 = -(mS[0]*zeta[0] + mS[1]*zeta[1] + mS[3]*zeta[2])*zeta[0]
    +      (mS[1]*zeta[0] + mS[2]*zeta[1] + mS[4]*zeta[2])*zeta[1]
    +      (mS[3]*zeta[0] + mS[4]*zeta[1] + mS[5]*zeta[2])*zeta[2];

  if( Vtx.fChi2 - dChi2 < 0 ) return;

  for(Int_t i=0;i<3;++i) 
    Vtx.fP[i] -= k0[i]*zeta[0] + k1[i]*zeta[1] + k2[i]*zeta[2];       
    
  //* New covariance matrix C -= K*(mCH')'
    
  for(Int_t i=0, k=0;i<3;++i){
    for(Int_t j=0;j<=i;++j,++k) 
      Vtx.fC[k] += k0[i]*mCHt0[j] + k1[i]*mCHt1[j] + k2[i]*mCHt2[j];
  }
    
  //* Calculate Chi^2 

  Vtx.fNDF  -= 2;
  Vtx.fChi2 -= dChi2;
}

void KFParticleBase::TransportLine( Double_t dS, 
                                       Double_t P[], Double_t C[] ) const 
{
  //* Transport the particle as a straight line

  P[0] = fP[0] + dS*fP[3];
  P[1] = fP[1] + dS*fP[4];
  P[2] = fP[2] + dS*fP[5];
  P[3] = fP[3];
  P[4] = fP[4];
  P[5] = fP[5];
  P[6] = fP[6];
  P[7] = fP[7];
 
  Double_t c6  = fC[ 6] + dS*fC[ 9];
  Double_t c11 = fC[11] + dS*fC[14];
  Double_t c17 = fC[17] + dS*fC[20];
  Double_t sc13 = dS*fC[13];
  Double_t sc18 = dS*fC[18];
  Double_t sc19 = dS*fC[19];

  C[ 0] = fC[ 0] + dS*( fC[ 6] + c6  );
  C[ 2] = fC[ 2] + dS*( fC[11] + c11 );
  C[ 5] = fC[ 5] + dS*( fC[17] + c17 );

  C[ 7] = fC[ 7] + sc13;
  C[ 8] = fC[ 8] + sc18;
  C[ 9] = fC[ 9];

  C[12] = fC[12] + sc19;

  C[ 1] = fC[ 1] + dS*( fC[10] + C[ 7] );
  C[ 3] = fC[ 3] + dS*( fC[15] + C[ 8] );
  C[ 4] = fC[ 4] + dS*( fC[16] + C[12] ); 
  C[ 6] = c6;

  C[10] = fC[10] + sc13;
  C[11] = c11;

  C[13] = fC[13];
  C[14] = fC[14];
  C[15] = fC[15] + sc18;
  C[16] = fC[16] + sc19;
  C[17] = c17;
  
  C[18] = fC[18];
  C[19] = fC[19];
  C[20] = fC[20];
  C[21] = fC[21] + dS*fC[24];
  C[22] = fC[22] + dS*fC[25];
  C[23] = fC[23] + dS*fC[26];

  C[24] = fC[24];
  C[25] = fC[25];
  C[26] = fC[26];
  C[27] = fC[27];
  C[28] = fC[28] + dS*fC[31];
  C[29] = fC[29] + dS*fC[32];
  C[30] = fC[30] + dS*fC[33];

  C[31] = fC[31];
  C[32] = fC[32];
  C[33] = fC[33];
  C[34] = fC[34];
  C[35] = fC[35]; 
}

void KFParticleBase::ConstructGammaBz( const KFParticleBase &daughter1,
                                          const KFParticleBase &daughter2, double Bz  )
{ 
  //* Create gamma
  
  const KFParticleBase *daughters[2] = { &daughter1, &daughter2};

  double v0[3];
  
  if( !fIsLinearized ){
    Double_t ds, ds1;
    Double_t m[8];
    Double_t mCd[36];       
    daughter1.GetDStoParticle(daughter2, ds, ds1);      
    daughter1.Transport( ds, m, mCd );
    fP[0] = m[0];
    fP[1] = m[1];
    fP[2] = m[2];
    daughter2.Transport( ds1, m, mCd );
    fP[0] = .5*( fP[0] + m[0] );
    fP[1] = .5*( fP[1] + m[1] );
    fP[2] = .5*( fP[2] + m[2] );
  } else {
    fP[0] = fVtxGuess[0];
    fP[1] = fVtxGuess[1];
    fP[2] = fVtxGuess[2];
  }

  double daughterP[2][8], daughterC[2][36];
  double vtxMom[2][3];

  int nIter = fIsLinearized ?1 :2;

  for( int iter=0; iter<nIter; iter++){

    v0[0] = fP[0];
    v0[1] = fP[1];
    v0[2] = fP[2];
    
    fAtProductionVertex = 0;
    fSFromDecay = 0;
    fP[0] = v0[0];
    fP[1] = v0[1];
    fP[2] = v0[2];
    fP[3] = 0;
    fP[4] = 0;
    fP[5] = 0;
    fP[6] = 0;
    fP[7] = 0;

  
    // fit daughters to the vertex guess  
    
    {  
      for( int id=0; id<2; id++ ){
        
        double *p = daughterP[id];
        double *mC = daughterC[id];
        
        daughters[id]->GetMeasurement( v0, p, mC );
        
        Double_t mAi[6];
        InvertSym3(mC, mAi );
        
        Double_t mB[3][3];
        
        mB[0][0] = mC[ 6]*mAi[0] + mC[ 7]*mAi[1] + mC[ 8]*mAi[3];
        mB[0][1] = mC[ 6]*mAi[1] + mC[ 7]*mAi[2] + mC[ 8]*mAi[4];
        mB[0][2] = mC[ 6]*mAi[3] + mC[ 7]*mAi[4] + mC[ 8]*mAi[5];
        
        mB[1][0] = mC[10]*mAi[0] + mC[11]*mAi[1] + mC[12]*mAi[3];
        mB[1][1] = mC[10]*mAi[1] + mC[11]*mAi[2] + mC[12]*mAi[4];
        mB[1][2] = mC[10]*mAi[3] + mC[11]*mAi[4] + mC[12]*mAi[5];
        
        mB[2][0] = mC[15]*mAi[0] + mC[16]*mAi[1] + mC[17]*mAi[3];
        mB[2][1] = mC[15]*mAi[1] + mC[16]*mAi[2] + mC[17]*mAi[4];
        mB[2][2] = mC[15]*mAi[3] + mC[16]*mAi[4] + mC[17]*mAi[5];
        
        Double_t z[3] = { v0[0]-p[0], v0[1]-p[1], v0[2]-p[2] };
        
        vtxMom[id][0] = p[3] + mB[0][0]*z[0] + mB[0][1]*z[1] + mB[0][2]*z[2];
        vtxMom[id][1] = p[4] + mB[1][0]*z[0] + mB[1][1]*z[1] + mB[1][2]*z[2];
        vtxMom[id][2] = p[5] + mB[2][0]*z[0] + mB[2][1]*z[1] + mB[2][2]*z[2];
        
        daughters[id]->Transport( daughters[id]->GetDStoPoint(v0), p, mC );
      
      }      
      
    } // fit daughters to guess

    
    // fit new vertex
    {
      
      double mpx0 =  vtxMom[0][0]+vtxMom[1][0];
      double mpy0 =  vtxMom[0][1]+vtxMom[1][1];
      double mpt0 = sqrt(mpx0*mpx0 + mpy0*mpy0);
      // double a0 = atan2(mpy0,mpx0);
      
      double ca0 = mpx0/mpt0;
      double sa0 = mpy0/mpt0;
      double r[3] = { v0[0], v0[1], v0[2] };
      double mC[3][3] = {{1000., 0 ,   0  },
                         {0,  1000.,   0  },
                         {0,     0, 1000. } };
      double chi2=0;
      
      for( int id=0; id<2; id++ ){              
        const Double_t kCLight = 0.000299792458;
        Double_t q = Bz*daughters[id]->GetQ()*kCLight;
        Double_t px0 = vtxMom[id][0];
        Double_t py0 = vtxMom[id][1];
        Double_t pz0 = vtxMom[id][2];
        Double_t pt0 = sqrt(px0*px0+py0*py0);
        Double_t mG[3][6], mB[3], mH[3][3];
        // r = {vx,vy,vz};
        // m = {x,y,z,Px,Py,Pz};
        // V = daughter.C
        // G*m + B = H*r;
        // q*x + Py - q*vx - sin(a)*Pt = 0
        // q*y - Px - q*vy + cos(a)*Pt = 0
        // (Px*cos(a) + Py*sin(a) ) (vz -z) - Pz( cos(a)*(vx-x) + sin(a)*(vy-y)) = 0
        
        mG[0][0] = q;
        mG[0][1] = 0;
        mG[0][2] = 0;
        mG[0][3] =   -sa0*px0/pt0;
        mG[0][4] = 1 -sa0*py0/pt0;
        mG[0][5] = 0;   
        mH[0][0] = q;
        mH[0][1] = 0;
        mH[0][2] = 0;      
        mB[0] = py0 - sa0*pt0 - mG[0][3]*px0 - mG[0][4]*py0 ;
        
        // q*y - Px - q*vy + cos(a)*Pt = 0
        
        mG[1][0] = 0;
        mG[1][1] = q;
        mG[1][2] = 0;
        mG[1][3] = -1 + ca0*px0/pt0;
        mG[1][4] =    + ca0*py0/pt0;
        mG[1][5] = 0;      
        mH[1][0] = 0;
        mH[1][1] = q;
        mH[1][2] = 0;      
        mB[1] = -px0 + ca0*pt0 - mG[1][3]*px0 - mG[1][4]*py0 ;
        
        // (Px*cos(a) + Py*sin(a) ) (z -vz) - Pz( cos(a)*(x-vx) + sin(a)*(y-vy)) = 0
      
        mG[2][0] = -pz0*ca0;
        mG[2][1] = -pz0*sa0;
        mG[2][2] =  px0*ca0 + py0*sa0;
        mG[2][3] = 0;
        mG[2][4] = 0;
        mG[2][5] = 0;
        
        mH[2][0] = mG[2][0];
        mH[2][1] = mG[2][1];
        mH[2][2] = mG[2][2];
        
        mB[2] = 0;
        
        // fit the vertex

        // V = GVGt

        double mGV[3][6];
        double mV[6];
        double m[3];
        for( int i=0; i<3; i++ ){
          m[i] = mB[i];
          for( int k=0; k<6; k++ ) m[i]+=mG[i][k]*daughterP[id][k];
        }
        for( int i=0; i<3; i++ ){
          for( int j=0; j<6; j++ ){
            mGV[i][j] = 0;
            for( int k=0; k<6; k++ ) mGV[i][j]+=mG[i][k]*daughterC[id][ IJ(k,j) ];
          }
        }
        for( int i=0, k=0; i<3; i++ ){
          for( int j=0; j<=i; j++,k++ ){
            mV[k] = 0;
            for( int l=0; l<6; l++ ) mV[k]+=mGV[i][l]*mG[j][l];
          }
        }
        
      
        //* CHt
        
        Double_t mCHt[3][3];
        Double_t mHCHt[6];
        Double_t mHr[3];
        for( int i=0; i<3; i++ ){         
          mHr[i] = 0;
          for( int k=0; k<3; k++ ) mHr[i]+= mH[i][k]*r[k];
        }
      
        for( int i=0; i<3; i++ ){
          for( int j=0; j<3; j++){
            mCHt[i][j] = 0;
            for( int k=0; k<3; k++ ) mCHt[i][j]+= mC[i][k]*mH[j][k];
          }
        }

        for( int i=0, k=0; i<3; i++ ){
          for( int j=0; j<=i; j++, k++ ){
            mHCHt[k] = 0;
            for( int l=0; l<3; l++ ) mHCHt[k]+= mH[i][l]*mCHt[l][j];
          }
        }
      
        Double_t mS[6] = { mHCHt[0]+mV[0], 
                           mHCHt[1]+mV[1], mHCHt[2]+mV[2], 
                           mHCHt[3]+mV[3], mHCHt[4]+mV[4], mHCHt[5]+mV[5]    }; 
      

        InvertSym3(mS,mS);
        
        //* Residual (measured - estimated)
    
        Double_t zeta[3] = { m[0]-mHr[0], m[1]-mHr[1], m[2]-mHr[2] };
            
        //* Kalman gain K = mCH'*S
    
        Double_t k[3][3];
      
        for(Int_t i=0;i<3;++i){
          k[i][0] = mCHt[i][0]*mS[0] + mCHt[i][1]*mS[1] + mCHt[i][2]*mS[3];
          k[i][1] = mCHt[i][0]*mS[1] + mCHt[i][1]*mS[2] + mCHt[i][2]*mS[4];
          k[i][2] = mCHt[i][0]*mS[3] + mCHt[i][1]*mS[4] + mCHt[i][2]*mS[5];
        }

        //* New estimation of the vertex position r += K*zeta
    
        for(Int_t i=0;i<3;++i) 
          r[i] = r[i] + k[i][0]*zeta[0] + k[i][1]*zeta[1] + k[i][2]*zeta[2];
      
        //* New covariance matrix C -= K*(mCH')'

        for(Int_t i=0;i<3;++i){
          for(Int_t j=0;j<=i;++j){
            mC[i][j] = mC[i][j] - (k[i][0]*mCHt[j][0] + k[i][1]*mCHt[j][1] + k[i][2]*mCHt[j][2]);
            mC[j][i] = mC[i][j];
          }
        }

        //* Calculate Chi^2 
        
        chi2 += ( ( mS[0]*zeta[0] + mS[1]*zeta[1] + mS[3]*zeta[2] )*zeta[0]
                  +(mS[1]*zeta[0] + mS[2]*zeta[1] + mS[4]*zeta[2] )*zeta[1]
                  +(mS[3]*zeta[0] + mS[4]*zeta[1] + mS[5]*zeta[2] )*zeta[2]  );  
      }
    
      // store vertex
    
      fNDF  = 2;
      fChi2 = chi2;
      for( int i=0; i<3; i++ ) fP[i] = r[i];
      for( int i=0,k=0; i<3; i++ ){
        for( int j=0; j<=i; j++,k++ ){
          fC[k] = mC[i][j];
        }
      }
    }

  } // iterations

  // now fit daughters to the vertex
  
  fQ     =  0;
  fSFromDecay = 0;    

  for(Int_t i=3;i<8;++i) fP[i]=0.;
  for(Int_t i=6;i<35;++i) fC[i]=0.;
  fC[35] = 100.;

  for( int id=0; id<2; id++ ){

    double *p = daughterP[id];
    double *mC = daughterC[id];      
    daughters[id]->GetMeasurement( v0, p, mC );

    const Double_t *m = fP, *mV = fC;
    
    Double_t mAi[6];
    InvertSym3(mC, mAi );

    Double_t mB[4][3];

    mB[0][0] = mC[ 6]*mAi[0] + mC[ 7]*mAi[1] + mC[ 8]*mAi[3];
    mB[0][1] = mC[ 6]*mAi[1] + mC[ 7]*mAi[2] + mC[ 8]*mAi[4];
    mB[0][2] = mC[ 6]*mAi[3] + mC[ 7]*mAi[4] + mC[ 8]*mAi[5];
    
    mB[1][0] = mC[10]*mAi[0] + mC[11]*mAi[1] + mC[12]*mAi[3];
    mB[1][1] = mC[10]*mAi[1] + mC[11]*mAi[2] + mC[12]*mAi[4];
    mB[1][2] = mC[10]*mAi[3] + mC[11]*mAi[4] + mC[12]*mAi[5];
    
    mB[2][0] = mC[15]*mAi[0] + mC[16]*mAi[1] + mC[17]*mAi[3];
    mB[2][1] = mC[15]*mAi[1] + mC[16]*mAi[2] + mC[17]*mAi[4];
    mB[2][2] = mC[15]*mAi[3] + mC[16]*mAi[4] + mC[17]*mAi[5];
    
    mB[3][0] = mC[21]*mAi[0] + mC[22]*mAi[1] + mC[23]*mAi[3];
    mB[3][1] = mC[21]*mAi[1] + mC[22]*mAi[2] + mC[23]*mAi[4];
    mB[3][2] = mC[21]*mAi[3] + mC[22]*mAi[4] + mC[23]*mAi[5];    


    Double_t z[3] = { m[0]-p[0], m[1]-p[1], m[2]-p[2] };

//     {
//       Double_t mAV[6] = { mC[0]-mV[0], mC[1]-mV[1], mC[2]-mV[2], 
//                        mC[3]-mV[3], mC[4]-mV[4], mC[5]-mV[5] };
//       
//       Double_t mAVi[6];
//       if( !InvertSym3(mAV, mAVi) ){
//      Double_t dChi2 = ( +(mAVi[0]*z[0] + mAVi[1]*z[1] + mAVi[3]*z[2])*z[0]
//                         +(mAVi[1]*z[0] + mAVi[2]*z[1] + mAVi[4]*z[2])*z[1]
//                         +(mAVi[3]*z[0] + mAVi[4]*z[1] + mAVi[5]*z[2])*z[2] );
//      fChi2+= fabs( dChi2 );
//       }
//       fNDF  += 2;
//     }

    //* Add the daughter momentum to the particle momentum
 
    fP[3]+= p[3] + mB[0][0]*z[0] + mB[0][1]*z[1] + mB[0][2]*z[2];
    fP[4]+= p[4] + mB[1][0]*z[0] + mB[1][1]*z[1] + mB[1][2]*z[2];
    fP[5]+= p[5] + mB[2][0]*z[0] + mB[2][1]*z[1] + mB[2][2]*z[2];
    fP[6]+= p[6] + mB[3][0]*z[0] + mB[3][1]*z[1] + mB[3][2]*z[2];
  
    Double_t d0, d1, d2;
   
    d0= mB[0][0]*mV[0] + mB[0][1]*mV[1] + mB[0][2]*mV[3] - mC[ 6];
    d1= mB[0][0]*mV[1] + mB[0][1]*mV[2] + mB[0][2]*mV[4] - mC[ 7];
    d2= mB[0][0]*mV[3] + mB[0][1]*mV[4] + mB[0][2]*mV[5] - mC[ 8];

    //fC[6]+= mC[ 6] + d0;
    //fC[7]+= mC[ 7] + d1;
    //fC[8]+= mC[ 8] + d2;
    fC[9]+= mC[ 9] + d0*mB[0][0] + d1*mB[0][1] + d2*mB[0][2];

    d0= mB[1][0]*mV[0] + mB[1][1]*mV[1] + mB[1][2]*mV[3] - mC[10];
    d1= mB[1][0]*mV[1] + mB[1][1]*mV[2] + mB[1][2]*mV[4] - mC[11];
    d2= mB[1][0]*mV[3] + mB[1][1]*mV[4] + mB[1][2]*mV[5] - mC[12];

    //fC[10]+= mC[10]+ d0;
    //fC[11]+= mC[11]+ d1;
    //fC[12]+= mC[12]+ d2;
    fC[13]+= mC[13]+ d0*mB[0][0] + d1*mB[0][1] + d2*mB[0][2];
    fC[14]+= mC[14]+ d0*mB[1][0] + d1*mB[1][1] + d2*mB[1][2];

    d0= mB[2][0]*mV[0] + mB[2][1]*mV[1] + mB[2][2]*mV[3] - mC[15];
    d1= mB[2][0]*mV[1] + mB[2][1]*mV[2] + mB[2][2]*mV[4] - mC[16];
    d2= mB[2][0]*mV[3] + mB[2][1]*mV[4] + mB[2][2]*mV[5] - mC[17];

    //fC[15]+= mC[15]+ d0;
    //fC[16]+= mC[16]+ d1;
    //fC[17]+= mC[17]+ d2;
    fC[18]+= mC[18]+ d0*mB[0][0] + d1*mB[0][1] + d2*mB[0][2];
    fC[19]+= mC[19]+ d0*mB[1][0] + d1*mB[1][1] + d2*mB[1][2];
    fC[20]+= mC[20]+ d0*mB[2][0] + d1*mB[2][1] + d2*mB[2][2];

    d0= mB[3][0]*mV[0] + mB[3][1]*mV[1] + mB[3][2]*mV[3] - mC[21];
    d1= mB[3][0]*mV[1] + mB[3][1]*mV[2] + mB[3][2]*mV[4] - mC[22];
    d2= mB[3][0]*mV[3] + mB[3][1]*mV[4] + mB[3][2]*mV[5] - mC[23];

    //fC[21]+= mC[21] + d0;
    //fC[22]+= mC[22] + d1;
    //fC[23]+= mC[23] + d2;
    fC[24]+= mC[24] + d0*mB[0][0] + d1*mB[0][1] + d2*mB[0][2];
    fC[25]+= mC[25] + d0*mB[1][0] + d1*mB[1][1] + d2*mB[1][2];
    fC[26]+= mC[26] + d0*mB[2][0] + d1*mB[2][1] + d2*mB[2][2];
    fC[27]+= mC[27] + d0*mB[3][0] + d1*mB[3][1] + d2*mB[3][2];
  }

//  SetMassConstraint(0,0);
  SetNonlinearMassConstraint(0);
}

void KFParticleBase::GetArmenterosPodolanski(KFParticleBase& positive, KFParticleBase& negative, Double_t QtAlfa[2] )
{
// example:
//       KFParticle PosParticle(...)
//       KFParticle NegParticle(...)
//       Gamma.ConstructGamma(PosParticle, NegParticle);
//       Double_t VertexGamma[3] = {Gamma.GetX(), Gamma.GetY(), Gamma.GetZ()};
//       PosParticle.TransportToPoint(VertexGamma);
//       NegParticle.TransportToPoint(VertexGamma);
//       Double_t armenterosQtAlfa[2] = {0.};
//       KFParticle::GetArmenterosPodolanski(PosParticle, NegParticle, armenterosQtAlfa );

  Double_t alpha = 0., qt = 0.;
  Double_t spx = positive.GetPx() + negative.GetPx();
  Double_t spy = positive.GetPy() + negative.GetPy();
  Double_t spz = positive.GetPz() + negative.GetPz();
  Double_t sp  = sqrt(spx*spx + spy*spy + spz*spz);
  if( sp == 0.0) return;
  Double_t pn, pp, pln, plp;

  pn = sqrt(negative.GetPx()*negative.GetPx() + negative.GetPy()*negative.GetPy() + negative.GetPz()*negative.GetPz());
  pp = sqrt(positive.GetPx()*positive.GetPx() + positive.GetPy()*positive.GetPy() + positive.GetPz()*positive.GetPz());
  pln  = (negative.GetPx()*spx+negative.GetPy()*spy+negative.GetPz()*spz)/sp;
  plp  = (positive.GetPx()*spx+positive.GetPy()*spy+positive.GetPz()*spz)/sp;

  if( pn == 0.0) return;
  Double_t ptm  = (1.-((pln/pn)*(pln/pn)));
  qt= (ptm>=0.)?  pn*sqrt(ptm) :0;
  alpha = (plp-pln)/(plp+pln);

  QtAlfa[0] = qt;
  QtAlfa[1] = alpha;
}

void KFParticleBase::RotateXY(Double_t angle, Double_t Vtx[3])
{
  // Rotates the KFParticle object around OZ axis, OZ axis is set by the vertex position
  // Double_t angle - angle of rotation in XY plane in [rad]
  // Double_t Vtx[3] - position of the vertex in [cm]

  // Before rotation the center of the coordinat system should be moved to the vertex position; move back after rotation
  X() = X() - Vtx[0];
  Y() = Y() - Vtx[1];
  Z() = Z() - Vtx[2];

  // Rotate the kf particle
  Double_t c = cos(angle);
  Double_t s = sin(angle);

  Double_t mA[8][ 8];
  for( Int_t i=0; i<8; i++ ){
    for( Int_t j=0; j<8; j++){
      mA[i][j] = 0;
    }
  }
  for( int i=0; i<8; i++ ){
    mA[i][i] = 1;
  }
  mA[0][0] =  c;  mA[0][1] = s;
  mA[1][0] = -s;  mA[1][1] = c;
  mA[3][3] =  c;  mA[3][4] = s;
  mA[4][3] = -s;  mA[4][4] = c;

  Double_t mAC[8][8];
  Double_t mAp[8];

  for( Int_t i=0; i<8; i++ ){
    mAp[i] = 0;
    for( Int_t k=0; k<8; k++){
      mAp[i]+=mA[i][k] * fP[k];
    }
  }

  for( Int_t i=0; i<8; i++){
    fP[i] = mAp[i];
  }

  for( Int_t i=0; i<8; i++ ){
    for( Int_t j=0; j<8; j++ ){
      mAC[i][j] = 0;
      for( Int_t k=0; k<8; k++ ){
        mAC[i][j]+= mA[i][k] * GetCovariance(k,j);
      }
    }
  }

  for( Int_t i=0; i<8; i++ ){
    for( Int_t j=0; j<=i; j++ ){
      Double_t xx = 0;
      for( Int_t k=0; k<8; k++){
        xx+= mAC[i][k]*mA[j][k];
      }
      Covariance(i,j) = xx;
    }
  }

  X() = GetX() + Vtx[0];
  Y() = GetY() + Vtx[1];
  Z() = GetZ() + Vtx[2];
}

Bool_t KFParticleBase::InvertSym3( const Double_t A[], Double_t Ai[] )
{
  //* Invert symmetric matric stored in low-triagonal form 

  bool ret = 0;
  double a0 = A[0], a1 = A[1], a2 = A[2], a3 = A[3];

  Ai[0] = a2*A[5] - A[4]*A[4];
  Ai[1] = a3*A[4] - a1*A[5];
  Ai[3] = a1*A[4] - a2*a3;
  Double_t det = (a0*Ai[0] + a1*Ai[1] + a3*Ai[3]);
  if( fabs(det)>1.e-20 ) det = 1./det;    
  else{ 
    det = 0;
    ret = 1;
  }
  Ai[0] *= det;
  Ai[1] *= det;
  Ai[3] *= det;
  Ai[2] = ( a0*A[5] - a3*a3 )*det;
  Ai[4] = ( a1*a3 - a0*A[4] )*det;
  Ai[5] = ( a0*a2 - a1*a1 )*det;
  return ret;
}

void KFParticleBase::MultQSQt( const Double_t Q[], const Double_t S[], Double_t SOut[] )
{
  //* Matrix multiplication Q*S*Q^T, Q - square matrix, S - symmetric

  const Int_t kN= 8;
  Double_t mA[kN*kN];
  
  for( Int_t i=0, ij=0; i<kN; i++ ){
    for( Int_t j=0; j<kN; j++, ++ij ){
      mA[ij] = 0 ;
      for( Int_t k=0; k<kN; ++k ) mA[ij]+= S[( k<=i ) ? i*(i+1)/2+k :k*(k+1)/2+i] * Q[ j*kN+k];
    }
  }
    
  for( Int_t i=0; i<kN; i++ ){
    for( Int_t j=0; j<=i; j++ ){
      Int_t ij = ( j<=i ) ? i*(i+1)/2+j :j*(j+1)/2+i;
      SOut[ij] = 0 ;
      for( Int_t k=0; k<kN; k++ )  SOut[ij] += Q[ i*kN+k ] * mA[ k*kN+j ];
    }
  }
}


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