source: git/external/TrackCovariance/ObsTrk.cc@ c18dca6

#include <TMath.h>
#include <TVector3.h>
#include <TMatrixD.h>
#include <TMatrixDSym.h>
#include <TDecompChol.h>
#include <TRandom.h>
#include <iostream>
#include "SolGridCov.h"
#include "ObsTrk.h"
//
// Constructors
// x(3) track origin, p(3) track momentum at origin, Q charge, B magnetic field in Tesla
ObsTrk::ObsTrk(TVector3 x, TVector3 p, Double_t Q, Double_t B, SolGridCov *GC)
{
        fGC = GC;
        fGenX = x;
        fGenP = p;
        fGenQ = Q;
        fB = B;
        fGenPar.ResizeTo(5);
        fGenParACTS.ResizeTo(6);
        fObsPar.ResizeTo(5);
        fObsParACTS.ResizeTo(6);
        fCov.ResizeTo(5, 5);
        fCovACTS.ResizeTo(6, 6);
        fGenPar = XPtoPar(x,p,Q);
        fGenParACTS = ParToACTS(fGenPar);
        /*
        std::cout << "ObsTrk::ObsTrk: fGenPar";
        for (Int_t i = 0; i < 5; i++)std::cout << fGenPar(i) << ", ";
        std::cout << std::endl;
        */
        fObsPar = GenToObsPar(fGenPar, fGC);
        fObsParACTS = ParToACTS(fObsPar);
        fObsX = ParToX(fObsPar);
        fObsP = ParToP(fObsPar);
        fObsQ = ParToQ(fObsPar);
        fCovACTS = CovToACTS(fCov);
}
//
// Destructor
ObsTrk::~ObsTrk()
{
        fGenX.Clear();
        fGenP.Clear();
        fGenPar.Clear();
        fGenParACTS.Clear();
        fObsX.Clear();
        fObsP.Clear();
        fObsPar.Clear();
        fObsParACTS.Clear();
        fCov.Clear();
        fCovACTS.Clear();
}
TVectorD ObsTrk::XPtoPar(TVector3 x, TVector3 p, Double_t Q)
{
        //
        TVectorD Par(5);
        // Transverse parameters
        Double_t a = -Q*fB*0.2998;                      // Units are Tesla, GeV and meters
        Double_t pt = p.Pt();
        Double_t C = a / (2 * pt);                      // Half curvature
        //std::cout << "ObsTrk::XPtoPar: fB = " << fB << ", a = " << a << ", pt = " << pt << ", C = " << C << std::endl;
        Double_t r2 = x.Perp2();
        Double_t cross = x(0)*p(1) - x(1)*p(0);
        Double_t T = TMath::Sqrt(pt*pt - 2 * a*cross + a*a*r2);
        Double_t phi0 = TMath::ATan2((p(1) - a*x(0)) / T, (p(0) + a*x(1)) / T); // Phi0
        Double_t D;                                                     // Impact parameter D
        if (pt < 10.0) D = (T - pt) / a;
        else D = (-2 * cross + a*r2) / (T + pt);
        //
        Par(0) = D;             // Store D
        Par(1) = phi0;  // Store phi0
        Par(2) = C;             // Store C
        //Longitudinal parameters
        Double_t B = C*TMath::Sqrt(TMath::Max(r2 - D*D,0.0) / (1 + 2 * C*D));
        Double_t st = TMath::ASin(B) / C;
        Double_t ct = p(2) / pt;
        Double_t z0 = x(2) - ct*st;
        //
        Par(3) = z0;            // Store z0
        Par(4) = ct;            // Store cot(theta)
        //
        return Par;
}
//
TVector3 ObsTrk::ParToX(TVectorD Par)
{
        Double_t D    = Par(0);
        Double_t phi0 = Par(1);
        Double_t z0   = Par(3);
        //
        TVector3 Xval;
        Xval(0) = -D*TMath::Sin(phi0); 
        Xval(1) =  D*TMath::Cos(phi0);  
        Xval(2) =  z0;
        //
        return Xval;
}
//
TVector3 ObsTrk::ParToP(TVectorD Par)
{
        Double_t C    = Par(2);
        Double_t phi0 = Par(1);
        Double_t ct   = Par(4);
        //
        TVector3 Pval;
        Double_t pt = fB*0.2998 / TMath::Abs(2 * C);
        Pval(0) = pt*TMath::Cos(phi0);
        Pval(1) = pt*TMath::Sin(phi0);
        Pval(2) = pt*ct;
        //
        return Pval;
}
//

Double_t ObsTrk::ParToQ(TVectorD Par)
{
        return TMath::Sign(1.0, -Par(2));
}
//
TVectorD ObsTrk::GenToObsPar(TVectorD gPar, SolGridCov *GC)
{
        TVector3 p = ParToP(gPar);
        Double_t pt = p.Pt();
        Double_t tanTh = 1.0 / TMath::Abs(gPar(4));
        Double_t angd = TMath::ATan(tanTh)*180. / TMath::Pi();
        //
        // Check ranges
        Double_t minPt = GC->GetMinPt ();
        if (pt < minPt) std::cout << "Warning ObsTrk::GenToObsPar: pt " << pt << " is below grid range of " << minPt << std::endl;
        Double_t maxPt = GC->GetMaxPt();
        if (pt > maxPt) std::cout << "Warning ObsTrk::GenToObsPar: pt " << pt << " is above grid range of " << maxPt << std::endl;
        Double_t minAn = GC->GetMinAng();
        if (angd < minAn) std::cout << "Warning ObsTrk::GenToObsPar: angle " << angd 
                << " is below grid range of " << minAn << std::endl;
        Double_t maxAn = GC->GetMaxAng();
        if (angd > maxAn) std::cout << "Warning ObsTrk::GenToObsPar: angle " << angd
                << " is above grid range of " << maxAn << std::endl;
        //
        TMatrixDSym Cov = GC->GetCov(pt, angd);
        fCov = Cov;
        //
        // Now do Choleski decomposition and random number extraction, with appropriate stabilization
        //
        TMatrixDSym CvN = Cov;
        TMatrixDSym DCv(5); DCv.Zero();
        TMatrixDSym DCvInv(5); DCvInv.Zero();
        for (Int_t id = 0; id < 5; id++)
        {
                Double_t dVal = TMath::Sqrt(Cov(id, id));
                DCv   (id, id) = dVal;
                DCvInv(id, id) = 1.0 / dVal;
        }
        CvN.Similarity(DCvInv);                 // Normalize diagonal to 1
        TDecompChol Chl(CvN);
        Bool_t OK = Chl.Decompose();            // Choleski decomposition of normalized matrix
        TMatrixD U = Chl.GetU();                        // Get Upper triangular matrix
        TMatrixD Ut(TMatrixD::kTransposed, U); // Transposed of U (lower triangular)
        TVectorD r(5);
        for (Int_t i = 0; i < 5; i++)r(i) = gRandom->Gaus(0.0, 1.0);            // Array of normal random numbers
        TVectorD oPar = gPar + DCv*(Ut*r);      // Observed parameter vector
        //
        return oPar;
}
// Parameter conversion to ACTS format
TVectorD ObsTrk::ParToACTS(TVectorD Par)
{
        TVectorD pACTS(6);      // Return vector
        //
        Double_t b = -0.29988*fB / 2.;
        pACTS(0) = 1000*Par(0);         // D from m to mm
        pACTS(1) = 1000 * Par(3);       // z0 from m to mm
        pACTS(2) = Par(1);                      // Phi0 is unchanged
        pACTS(3) = TMath::ATan(1.0 / Par(4)) + TMath::PiOver2();                // Theta in [0, pi] range
        pACTS(4) = Par(2) / (b*TMath::Sqrt(1 + Par(4)*Par(4)));         // q/p in GeV
        pACTS(5) = 0.0;                         // Time: currently undefined
        //
        return pACTS;
}
// Covariance conversion to ACTS format
TMatrixDSym ObsTrk::CovToACTS(TMatrixDSym Cov)
{
        TMatrixDSym cACTS(6); cACTS.Zero();
        Double_t b = -0.29988*fB / 2.;
        //
        // Fill derivative matrix
        TMatrixD A(5, 5);       A.Zero();
        Double_t ct = fGenPar(4);       // cot(theta)
        Double_t C = fGenPar(2);                // half curvature
        A(0, 0) = 1000.;                // D-D  conversion to mm
        A(1, 2) = 1.0;          // phi0-phi0
        A(2, 4) = 1.0/(TMath::Sqrt(1.0 + ct*ct) * b);   // q/p-C
        A(3, 1) = 1000.;                // z0-z0 conversion to mm
        A(4, 3) = -1.0 / (1.0 + ct*ct); // theta - cot(theta)
        A(4, 4) = -C*ct / (b*pow(1.0 + ct*ct,3.0/2.0)); // q/p-cot(theta)
        //
        TMatrixDSym Cv = Cov;
        TMatrixD At(5, 5);
        At.Transpose(A);
        Cv.Similarity(At);
        TMatrixDSub(cACTS, 0, 4, 0, 4) = Cv;
        cACTS(5, 5) = 0.1;      // Currently undefined: set to arbitrary value to avoid crashes
        //
        return cACTS;
}