-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)
- Warning("GetDCA"," stopped at not a stationary point !\n");
- Double_t lmb=h11+h22; lmb=lmb-TMath::Sqrt(lmb*lmb-4*det);
- if (lmb < 0.)
- Warning("GetDCA"," stopped at not a minimum !\n");
- 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) {
- Warning("GetDCA"," overshoot !\n"); break;
- }
- }
- dm=dd;
-
- t1+=dt1;
- t2+=dt2;
-
- }
-
- if (max<=0) Warning("GetDCA"," too many iterations !\n");
-
- 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));