[u/mrichter/AliRoot.git] / STEER / AliKalmanTrack.cxx

/**************************************************************************
 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
 *                                                                        *
 * Author: The ALICE Off-line Project.                                    *
 * Contributors are mentioned in the code where appropriate.              *
 *                                                                        *
 * Permission to use, copy, modify and distribute this software and its   *
 * documentation strictly for non-commercial purposes is hereby granted   *
 * without fee, provided that the above copyright notice appears in all   *
 * copies and that both the copyright notice and this permission notice   *
 * appear in the supporting documentation. The authors make no claims     *
 * about the suitability of this software for any purpose. It is          *
 * provided "as is" without express or implied warranty.                  *
 **************************************************************************/

/* $Id$ */

//-------------------------------------------------------------------------
//                Implementation of the AliKalmanTrack class
//   that is the base for AliTPCtrack, AliITStrackV2 and AliTRDtrack
//        Origin: Iouri Belikov, CERN, Jouri.Belikov@cern.ch
//-------------------------------------------------------------------------

#include "AliKalmanTrack.h"
#include "AliLog.h"

ClassImp(AliKalmanTrack)

Double_t AliKalmanTrack::fgConvConst;

//_______________________________________________________________________
AliKalmanTrack::AliKalmanTrack():
  fLab(-3141593),
  fFakeRatio(0),
  fChi2(0),
  fMass(AliPID::ParticleMass(AliPID::kPion)),
  fN(0)
{
  //
  // Default constructor
  //
    if (fgConvConst==0) {
      AliFatal("The magnetic field has not been set!");
    }
    
    fStartTimeIntegral = kFALSE;
    fIntegratedLength = 0;
    for(Int_t i=0; i<5; i++) fIntegratedTime[i] = 0;
}

//_______________________________________________________________________
AliKalmanTrack::AliKalmanTrack(const AliKalmanTrack &t):
  TObject(t),
  fLab(t.fLab),
  fFakeRatio(t.fFakeRatio),
  fChi2(t.fChi2),
  fMass(t.fMass),
  fN(t.fN)
{
  //
  // Copy constructor
  //
  if (fgConvConst==0) {
    AliFatal("The magnetic field has not been set!");
  }

  fStartTimeIntegral = t.fStartTimeIntegral;
  fIntegratedLength = t.fIntegratedLength;
  
  for (Int_t i=0; i<5; i++) 
    fIntegratedTime[i] = t.fIntegratedTime[i];
}

//_______________________________________________________________________
void AliKalmanTrack::StartTimeIntegral() 
{
  // Sylwester Radomski, GSI
  // S.Radomski@gsi.de
  //
  // Start time integration
  // To be called at Vertex by ITS tracker
  //
  
  //if (fStartTimeIntegral) 
  //  AliWarning("Reseting Recorded Time.");

  fStartTimeIntegral = kTRUE;
  for(Int_t i=0; i<AliPID::kSPECIES; i++) fIntegratedTime[i] = 0;  
  fIntegratedLength = 0;
}
//_______________________________________________________________________
void AliKalmanTrack:: AddTimeStep(Double_t length) 
{
  // 
  // Add step to integrated time
  // this method should be called by a sublasses at the end
  // of the PropagateTo function or by a tracker
  // each time step is made.
  //
  // If integration not started function does nothing
  //
  // Formula
  // dt = dl * sqrt(p^2 + m^2) / p
  // p = pT * (1 + tg^2 (lambda) )
  //
  // pt = 1/external parameter [4]
  // tg lambda = external parameter [3]
  //
  //
  // Sylwester Radomski, GSI
  // S.Radomski@gsi.de
  // 
  
  static const Double_t kcc = 2.99792458e-2;

  if (!fStartTimeIntegral) return;
  
  fIntegratedLength += length;

  Double_t xr, param[5];
  Double_t pt, tgl;
  
  GetExternalParameters(xr, param);
  pt =  1/param[4] ;
  tgl = param[3];

  Double_t p = TMath::Abs(pt * TMath::Sqrt(1+tgl*tgl));

  if (length > 100) return;

  for (Int_t i=0; i<AliPID::kSPECIES; i++) {
    
    Double_t mass = AliPID::ParticleMass(i);
    Double_t correction = TMath::Sqrt( pt*pt * (1 + tgl*tgl) + mass * mass ) / p;
    Double_t time = length * correction / kcc;

    fIntegratedTime[i] += time;
  }
}

//_______________________________________________________________________

Double_t AliKalmanTrack::GetIntegratedTime(Int_t pdg) const 
{
  // Sylwester Radomski, GSI
  // S.Radomski@gsi.de
  //
  // Return integrated time hypothesis for a given particle
  // type assumption.
  //
  // Input parameter:
  // pdg - Pdg code of a particle type
  //


  if (!fStartTimeIntegral) {
    AliWarning("Time integration not started");
    return 0.;
  }

  for (Int_t i=0; i<AliPID::kSPECIES; i++)
    if (AliPID::ParticleCode(i) == TMath::Abs(pdg)) return fIntegratedTime[i];

  AliWarning(Form("Particle type [%d] not found", pdg));
  return 0;
}

void AliKalmanTrack::GetIntegratedTimes(Double_t *times) const {
  for (Int_t i=0; i<AliPID::kSPECIES; i++) times[i]=fIntegratedTime[i];
}

void AliKalmanTrack::SetIntegratedTimes(const Double_t *times) {
  for (Int_t i=0; i<AliPID::kSPECIES; i++) fIntegratedTime[i]=times[i];
}

//_______________________________________________________________________

void AliKalmanTrack::PrintTime() const
{
  // Sylwester Radomski, GSI
  // S.Radomski@gsi.de
  //
  // For testing
  // Prints time for all hypothesis
  //

  for (Int_t i=0; i<AliPID::kSPECIES; i++)
    printf("%d: %.2f  ", AliPID::ParticleCode(i), fIntegratedTime[i]);
  printf("\n");  
}

static void External2Helix(const AliKalmanTrack *t, Double_t helix[6]) { 
  //--------------------------------------------------------------------
  // External track parameters -> helix parameters 
  //--------------------------------------------------------------------
  Double_t alpha,x,cs,sn;
  t->GetExternalParameters(x,helix); alpha=t->GetAlpha();

  cs=TMath::Cos(alpha); sn=TMath::Sin(alpha);
  helix[5]=x*cs - helix[0]*sn;            // x0
  helix[0]=x*sn + helix[0]*cs;            // y0
//helix[1]=                               // z0
  helix[2]=TMath::ASin(helix[2]) + alpha; // phi0
//helix[3]=                               // tgl
  helix[4]=helix[4]/t->GetConvConst();    // C
}

static void Evaluate(const Double_t *h, Double_t t,
                     Double_t r[3],  //radius vector
                     Double_t g[3],  //first defivatives
                     Double_t gg[3]) //second derivatives
{
  //--------------------------------------------------------------------
  // Calculate position of a point on a track and some derivatives
  //--------------------------------------------------------------------
  Double_t phase=h[4]*t+h[2];
  Double_t sn=TMath::Sin(phase), cs=TMath::Cos(phase);

  r[0] = h[5] + (sn - h[6])/h[4];
  r[1] = h[0] - (cs - h[7])/h[4];  
  r[2] = h[1] + h[3]*t;

  g[0] = cs; g[1]=sn; g[2]=h[3];
  
  gg[0]=-h[4]*sn; gg[1]=h[4]*cs; gg[2]=0.;
}

Double_t AliKalmanTrack::
GetDCA(const AliKalmanTrack *p, Double_t &xthis, Double_t &xp) const {
  //------------------------------------------------------------
  // Returns the (weighed !) distance of closest approach between 
  // this track and the track passed as the argument.
  // Other returned values:
  //   xthis, xt - coordinates of tracks' reference planes at the DCA 
  //-----------------------------------------------------------
  Double_t dy2=GetSigmaY2() + p->GetSigmaY2();
  Double_t dz2=GetSigmaZ2() + p->GetSigmaZ2();
  Double_t dx2=dy2; 

  //dx2=dy2=dz2=1.;

  Double_t p1[8]; External2Helix(this,p1);
  p1[6]=TMath::Sin(p1[2]); p1[7]=TMath::Cos(p1[2]);
  Double_t p2[8]; External2Helix(p,p2);
  p2[6]=TMath::Sin(p2[2]); p2[7]=TMath::Cos(p2[2]);


  Double_t r1[3],g1[3],gg1[3]; Double_t t1=0.;
  Evaluate(p1,t1,r1,g1,gg1);
  Double_t r2[3],g2[3],gg2[3]; Double_t t2=0.;
  Evaluate(p2,t2,r2,g2,gg2);

  Double_t dx=r2[0]-r1[0], dy=r2[1]-r1[1], dz=r2[2]-r1[2];
  Double_t dm=dx*dx/dx2 + dy*dy/dy2 + dz*dz/dz2;

  Int_t max=27;
  while (max--) {
     Double_t gt1=-(dx*g1[0]/dx2 + dy*g1[1]/dy2 + dz*g1[2]/dz2);
     Double_t gt2=+(dx*g2[0]/dx2 + dy*g2[1]/dy2 + dz*g2[2]/dz2);
     Double_t h11=(g1[0]*g1[0] - dx*gg1[0])/dx2 + 
                  (g1[1]*g1[1] - dy*gg1[1])/dy2 +
                  (g1[2]*g1[2] - dz*gg1[2])/dz2;
     Double_t h22=(g2[0]*g2[0] + dx*gg2[0])/dx2 + 
                  (g2[1]*g2[1] + dy*gg2[1])/dy2 +
                  (g2[2]*g2[2] + dz*gg2[2])/dz2;
     Double_t h12=-(g1[0]*g2[0]/dx2 + g1[1]*g2[1]/dy2 + g1[2]*g2[2]/dz2);

     Double_t det=h11*h22-h12*h12;

     Double_t dt1,dt2;
     if (TMath::Abs(det)<1.e-33) {
        //(quasi)singular Hessian
        dt1=-gt1; dt2=-gt2;
     } else {
        dt1=-(gt1*h22 - gt2*h12)/det; 
        dt2=-(h11*gt2 - h12*gt1)/det;
     }

     if ((dt1*gt1+dt2*gt2)>0) {dt1=-dt1; dt2=-dt2;}

     //check delta(phase1) ?
     //check delta(phase2) ?

     if (TMath::Abs(dt1)/(TMath::Abs(t1)+1.e-3) < 1.e-4)
     if (TMath::Abs(dt2)/(TMath::Abs(t2)+1.e-3) < 1.e-4) {
        if ((gt1*gt1+gt2*gt2) > 1.e-4/dy2/dy2) 
	  AliWarning(" stopped at not a stationary point !");
        Double_t lmb=h11+h22; lmb=lmb-TMath::Sqrt(lmb*lmb-4*det);
        if (lmb < 0.) 
	  AliWarning(" stopped at not a minimum !");
        break;
     }

     Double_t dd=dm;
     for (Int_t div=1 ; ; div*=2) {
        Evaluate(p1,t1+dt1,r1,g1,gg1);
        Evaluate(p2,t2+dt2,r2,g2,gg2);
        dx=r2[0]-r1[0]; dy=r2[1]-r1[1]; dz=r2[2]-r1[2];
        dd=dx*dx/dx2 + dy*dy/dy2 + dz*dz/dz2;
	if (dd<dm) break;
        dt1*=0.5; dt2*=0.5;
        if (div>512) {
           AliWarning(" overshoot !"); break;
        }   
     }
     dm=dd;

     t1+=dt1;
     t2+=dt2;

  }

  if (max<=0) AliWarning(" too many iterations !");

  Double_t cs=TMath::Cos(GetAlpha());
  Double_t sn=TMath::Sin(GetAlpha());
  xthis=r1[0]*cs + r1[1]*sn;

  cs=TMath::Cos(p->GetAlpha());
  sn=TMath::Sin(p->GetAlpha());
  xp=r2[0]*cs + r2[1]*sn;

  return TMath::Sqrt(dm*TMath::Sqrt(dy2*dz2));
}

Double_t AliKalmanTrack::
PropagateToDCA(AliKalmanTrack *p, Double_t d, Double_t x0) {
  //--------------------------------------------------------------
  // Propagates this track and the argument track to the position of the
  // distance of closest approach. 
  // Returns the (weighed !) distance of closest approach.
  //--------------------------------------------------------------
  Double_t xthis,xp;
  Double_t dca=GetDCA(p,xthis,xp);

  if (!PropagateTo(xthis,d,x0)) {
    //AliWarning(" propagation failed !");
    return 1e+33;
  }  

  if (!p->PropagateTo(xp,d,x0)) {
    //AliWarning(" propagation failed !";
    return 1e+33;
  }  

  return dca;
}
Commit	Line	Data
	1	/**************************************************************************
	2	* Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
	3	* *
	4	* Author: The ALICE Off-line Project. *
	5	* Contributors are mentioned in the code where appropriate. *
	6	* *
	7	* Permission to use, copy, modify and distribute this software and its *
	8	* documentation strictly for non-commercial purposes is hereby granted *
	9	* without fee, provided that the above copyright notice appears in all *
	10	* copies and that both the copyright notice and this permission notice *
	11	* appear in the supporting documentation. The authors make no claims *
	12	* about the suitability of this software for any purpose. It is *
	13	* provided "as is" without express or implied warranty. *
	14	**************************************************************************/
	15
	16	/* $Id$ */
	17
	18	//-------------------------------------------------------------------------
	19	// Implementation of the AliKalmanTrack class
	20	// that is the base for AliTPCtrack, AliITStrackV2 and AliTRDtrack
	21	// Origin: Iouri Belikov, CERN, Jouri.Belikov@cern.ch
	22	//-------------------------------------------------------------------------
	23
	24	#include "AliKalmanTrack.h"
	25	#include "AliLog.h"
	26
	27	ClassImp(AliKalmanTrack)
	28
	29	Double_t AliKalmanTrack::fgConvConst;
	30
	31	//_______________________________________________________________________
	32	AliKalmanTrack::AliKalmanTrack():
	33	fLab(-3141593),
	34	fFakeRatio(0),
	35	fChi2(0),
	36	fMass(AliPID::ParticleMass(AliPID::kPion)),
	37	fN(0)
	38	{
	39	//
	40	// Default constructor
	41	//
	42	if (fgConvConst==0) {
	43	AliFatal("The magnetic field has not been set!");
	44	}
	45
	46	fStartTimeIntegral = kFALSE;
	47	fIntegratedLength = 0;
	48	for(Int_t i=0; i<5; i++) fIntegratedTime[i] = 0;
	49	}
	50
	51	//_______________________________________________________________________
	52	AliKalmanTrack::AliKalmanTrack(const AliKalmanTrack &t):
	53	TObject(t),
	54	fLab(t.fLab),
	55	fFakeRatio(t.fFakeRatio),
	56	fChi2(t.fChi2),
	57	fMass(t.fMass),
	58	fN(t.fN)
	59	{
	60	//
	61	// Copy constructor
	62	//
	63	if (fgConvConst==0) {
	64	AliFatal("The magnetic field has not been set!");
	65	}
	66
	67	fStartTimeIntegral = t.fStartTimeIntegral;
	68	fIntegratedLength = t.fIntegratedLength;
	69
	70	for (Int_t i=0; i<5; i++)
	71	fIntegratedTime[i] = t.fIntegratedTime[i];
	72	}
	73
	74	//_______________________________________________________________________
	75	void AliKalmanTrack::StartTimeIntegral()
	76	{
	77	// Sylwester Radomski, GSI
	78	// S.Radomski@gsi.de
	79	//
	80	// Start time integration
	81	// To be called at Vertex by ITS tracker
	82	//
	83
	84	//if (fStartTimeIntegral)
	85	// AliWarning("Reseting Recorded Time.");
	86
	87	fStartTimeIntegral = kTRUE;
	88	for(Int_t i=0; i<AliPID::kSPECIES; i++) fIntegratedTime[i] = 0;
	89	fIntegratedLength = 0;
	90	}
	91	//_______________________________________________________________________
	92	void AliKalmanTrack:: AddTimeStep(Double_t length)
	93	{
	94	//
	95	// Add step to integrated time
	96	// this method should be called by a sublasses at the end
	97	// of the PropagateTo function or by a tracker
	98	// each time step is made.
	99	//
	100	// If integration not started function does nothing
	101	//
	102	// Formula
	103	// dt = dl * sqrt(p^2 + m^2) / p
	104	// p = pT * (1 + tg^2 (lambda) )
	105	//
	106	// pt = 1/external parameter [4]
	107	// tg lambda = external parameter [3]
	108	//
	109	//
	110	// Sylwester Radomski, GSI
	111	// S.Radomski@gsi.de
	112	//
	113
	114	static const Double_t kcc = 2.99792458e-2;
	115
	116	if (!fStartTimeIntegral) return;
	117
	118	fIntegratedLength += length;
	119
	120	Double_t xr, param[5];
	121	Double_t pt, tgl;
	122
	123	GetExternalParameters(xr, param);
	124	pt = 1/param[4] ;
	125	tgl = param[3];
	126
	127	Double_t p = TMath::Abs(pt * TMath::Sqrt(1+tgl*tgl));
	128
	129	if (length > 100) return;
	130
	131	for (Int_t i=0; i<AliPID::kSPECIES; i++) {
	132
	133	Double_t mass = AliPID::ParticleMass(i);
	134	Double_t correction = TMath::Sqrt( ptpt (1 + tgltgl) + mass mass ) / p;
	135	Double_t time = length * correction / kcc;
	136
	137	fIntegratedTime[i] += time;
	138	}
	139	}
	140
	141	//_______________________________________________________________________
	142
	143	Double_t AliKalmanTrack::GetIntegratedTime(Int_t pdg) const
	144	{
	145	// Sylwester Radomski, GSI
	146	// S.Radomski@gsi.de
	147	//
	148	// Return integrated time hypothesis for a given particle
	149	// type assumption.
	150	//
	151	// Input parameter:
	152	// pdg - Pdg code of a particle type
	153	//
	154
	155
	156	if (!fStartTimeIntegral) {
	157	AliWarning("Time integration not started");
	158	return 0.;
	159	}
	160
	161	for (Int_t i=0; i<AliPID::kSPECIES; i++)
	162	if (AliPID::ParticleCode(i) == TMath::Abs(pdg)) return fIntegratedTime[i];
	163
	164	AliWarning(Form("Particle type [%d] not found", pdg));
	165	return 0;
	166	}
	167
	168	void AliKalmanTrack::GetIntegratedTimes(Double_t *times) const {
	169	for (Int_t i=0; i<AliPID::kSPECIES; i++) times[i]=fIntegratedTime[i];
	170	}
	171
	172	void AliKalmanTrack::SetIntegratedTimes(const Double_t *times) {
	173	for (Int_t i=0; i<AliPID::kSPECIES; i++) fIntegratedTime[i]=times[i];
	174	}
	175
	176	//_______________________________________________________________________
	177
	178	void AliKalmanTrack::PrintTime() const
	179	{
	180	// Sylwester Radomski, GSI
	181	// S.Radomski@gsi.de
	182	//
	183	// For testing
	184	// Prints time for all hypothesis
	185	//
	186
	187	for (Int_t i=0; i<AliPID::kSPECIES; i++)
	188	printf("%d: %.2f ", AliPID::ParticleCode(i), fIntegratedTime[i]);
	189	printf("\n");
	190	}
	191
	192	static void External2Helix(const AliKalmanTrack *t, Double_t helix[6]) {
	193	//--------------------------------------------------------------------
	194	// External track parameters -> helix parameters
	195	//--------------------------------------------------------------------
	196	Double_t alpha,x,cs,sn;
	197	t->GetExternalParameters(x,helix); alpha=t->GetAlpha();
	198
	199	cs=TMath::Cos(alpha); sn=TMath::Sin(alpha);
	200	helix[5]=xcs - helix[0]sn; // x0
	201	helix[0]=xsn + helix[0]cs; // y0
	202	//helix[1]= // z0
	203	helix[2]=TMath::ASin(helix[2]) + alpha; // phi0
	204	//helix[3]= // tgl
	205	helix[4]=helix[4]/t->GetConvConst(); // C
	206	}
	207
	208	static void Evaluate(const Double_t *h, Double_t t,
	209	Double_t r[3], //radius vector
	210	Double_t g[3], //first defivatives
	211	Double_t gg[3]) //second derivatives
	212	{
	213	//--------------------------------------------------------------------
	214	// Calculate position of a point on a track and some derivatives
	215	//--------------------------------------------------------------------
	216	Double_t phase=h[4]*t+h[2];
	217	Double_t sn=TMath::Sin(phase), cs=TMath::Cos(phase);
	218
	219	r[0] = h[5] + (sn - h[6])/h[4];
	220	r[1] = h[0] - (cs - h[7])/h[4];
	221	r[2] = h[1] + h[3]*t;
	222
	223	g[0] = cs; g[1]=sn; g[2]=h[3];
	224
	225	gg[0]=-h[4]sn; gg[1]=h[4]cs; gg[2]=0.;
	226	}
	227
	228	Double_t AliKalmanTrack::
	229	GetDCA(const AliKalmanTrack *p, Double_t &xthis, Double_t &xp) const {
	230	//------------------------------------------------------------
	231	// Returns the (weighed !) distance of closest approach between
	232	// this track and the track passed as the argument.
	233	// Other returned values:
	234	// xthis, xt - coordinates of tracks' reference planes at the DCA
	235	//-----------------------------------------------------------
	236	Double_t dy2=GetSigmaY2() + p->GetSigmaY2();
	237	Double_t dz2=GetSigmaZ2() + p->GetSigmaZ2();
	238	Double_t dx2=dy2;
	239
	240	//dx2=dy2=dz2=1.;
	241
	242	Double_t p1[8]; External2Helix(this,p1);
	243	p1[6]=TMath::Sin(p1[2]); p1[7]=TMath::Cos(p1[2]);
	244	Double_t p2[8]; External2Helix(p,p2);
	245	p2[6]=TMath::Sin(p2[2]); p2[7]=TMath::Cos(p2[2]);
	246
	247
	248	Double_t r1[3],g1[3],gg1[3]; Double_t t1=0.;
	249	Evaluate(p1,t1,r1,g1,gg1);
	250	Double_t r2[3],g2[3],gg2[3]; Double_t t2=0.;
	251	Evaluate(p2,t2,r2,g2,gg2);
	252
	253	Double_t dx=r2[0]-r1[0], dy=r2[1]-r1[1], dz=r2[2]-r1[2];
	254	Double_t dm=dxdx/dx2 + dydy/dy2 + dz*dz/dz2;
	255
	256	Int_t max=27;
	257	while (max--) {
	258	Double_t gt1=-(dxg1[0]/dx2 + dyg1[1]/dy2 + dz*g1[2]/dz2);
	259	Double_t gt2=+(dxg2[0]/dx2 + dyg2[1]/dy2 + dz*g2[2]/dz2);
	260	Double_t h11=(g1[0]g1[0] - dxgg1[0])/dx2 +
	261	(g1[1]g1[1] - dygg1[1])/dy2 +
	262	(g1[2]g1[2] - dzgg1[2])/dz2;
	263	Double_t h22=(g2[0]g2[0] + dxgg2[0])/dx2 +
	264	(g2[1]g2[1] + dygg2[1])/dy2 +
	265	(g2[2]g2[2] + dzgg2[2])/dz2;
	266	Double_t h12=-(g1[0]g2[0]/dx2 + g1[1]g2[1]/dy2 + g1[2]*g2[2]/dz2);
	267
	268	Double_t det=h11h22-h12h12;
	269
	270	Double_t dt1,dt2;
	271	if (TMath::Abs(det)<1.e-33) {
	272	//(quasi)singular Hessian
	273	dt1=-gt1; dt2=-gt2;
	274	} else {
	275	dt1=-(gt1h22 - gt2h12)/det;
	276	dt2=-(h11gt2 - h12gt1)/det;
	277	}
	278
	279	if ((dt1gt1+dt2gt2)>0) {dt1=-dt1; dt2=-dt2;}
	280
	281	//check delta(phase1) ?
	282	//check delta(phase2) ?
	283
	284	if (TMath::Abs(dt1)/(TMath::Abs(t1)+1.e-3) < 1.e-4)
	285	if (TMath::Abs(dt2)/(TMath::Abs(t2)+1.e-3) < 1.e-4) {
	286	if ((gt1gt1+gt2gt2) > 1.e-4/dy2/dy2)
	287	AliWarning(" stopped at not a stationary point !");
	288	Double_t lmb=h11+h22; lmb=lmb-TMath::Sqrt(lmblmb-4det);
	289	if (lmb < 0.)
	290	AliWarning(" stopped at not a minimum !");
	291	break;
	292	}
	293
	294	Double_t dd=dm;
	295	for (Int_t div=1 ; ; div*=2) {
	296	Evaluate(p1,t1+dt1,r1,g1,gg1);
	297	Evaluate(p2,t2+dt2,r2,g2,gg2);
	298	dx=r2[0]-r1[0]; dy=r2[1]-r1[1]; dz=r2[2]-r1[2];
	299	dd=dxdx/dx2 + dydy/dy2 + dz*dz/dz2;
	300	if (dd<dm) break;
	301	dt1=0.5; dt2=0.5;
	302	if (div>512) {
	303	AliWarning(" overshoot !"); break;
	304	}
	305	}
	306	dm=dd;
	307
	308	t1+=dt1;
	309	t2+=dt2;
	310
	311	}
	312
	313	if (max<=0) AliWarning(" too many iterations !");
	314
	315	Double_t cs=TMath::Cos(GetAlpha());
	316	Double_t sn=TMath::Sin(GetAlpha());
	317	xthis=r1[0]cs + r1[1]sn;
	318
	319	cs=TMath::Cos(p->GetAlpha());
	320	sn=TMath::Sin(p->GetAlpha());
	321	xp=r2[0]cs + r2[1]sn;
	322
	323	return TMath::Sqrt(dmTMath::Sqrt(dy2dz2));
	324	}
	325
	326	Double_t AliKalmanTrack::
	327	PropagateToDCA(AliKalmanTrack *p, Double_t d, Double_t x0) {
	328	//--------------------------------------------------------------
	329	// Propagates this track and the argument track to the position of the
	330	// distance of closest approach.
	331	// Returns the (weighed !) distance of closest approach.
	332	//--------------------------------------------------------------
	333	Double_t xthis,xp;
	334	Double_t dca=GetDCA(p,xthis,xp);
	335
	336	if (!PropagateTo(xthis,d,x0)) {
	337	//AliWarning(" propagation failed !");
	338	return 1e+33;
	339	}
	340
	341	if (!p->PropagateTo(xp,d,x0)) {
	342	//AliWarning(" propagation failed !";
	343	return 1e+33;
	344	}
	345
	346	return dca;
	347	}