---

CSCSegAlgoSK Class Reference

This is the original algorithm for building endcap muon track segments out of the rechit's in a CSCChamber. More...

#include <RecoLocalMuon/CSCSegment/src/CSCSegAlgoSK.h>

Inheritance diagram for CSCSegAlgoSK:

List of all members.

Public Types
typedef std::deque< bool >	BoolContainer
typedef std::vector< const CSCRecHit2D * >	ChamberHitContainer
typedef std::vector< const CSCRecHit2D * > ::const_iterator	ChamberHitContainerCIt
typedef std::vector< int >	LayerIndex
	Typedefs.
Public Member Functions
std::vector< CSCSegment >	buildSegments (ChamberHitContainer rechits)
	Build track segments in this chamber (this is where the actual segment-building algorithm hides.
	CSCSegAlgoSK (const edm::ParameterSet &ps)
	Constructor.
std::vector< CSCSegment >	run (const CSCChamber *aChamber, ChamberHitContainer rechits)
	Here we must implement the algorithm.
virtual	~CSCSegAlgoSK ()
	Destructor.
Private Member Functions
bool	addHit (const CSCRecHit2D *hit, int layer)
	Utility functions.
bool	areHitsCloseInGlobalPhi (const CSCRecHit2D *h1, const CSCRecHit2D *h2) const
bool	areHitsCloseInLocalX (const CSCRecHit2D *h1, const CSCRecHit2D *h2) const
	Utility functions.
AlgebraicSymMatrix	calculateError (void) const
void	compareProtoSegment (const CSCRecHit2D *h, int layer)
HepMatrix	derivativeMatrix (void) const
void	dumpHits (const ChamberHitContainer &rechits) const
	Dump position and phi of each rechit in chamber after sort in z.
void	fillChiSquared (void)
void	fillLocalDirection (void)
	Always enforce direction of segment to point from IP outwards (Incorrect for particles not coming from IP, of course.
void	fitSlopes (void)
void	flagHitsAsUsed (const ChamberHitContainer &rechitsInChamber, BoolContainer &used) const
	Flag hits on segment as used.
void	flipErrors (AlgebraicSymMatrix &) const
bool	hasHitOnLayer (int layer) const
void	increaseProtoSegment (const CSCRecHit2D *h, int layer)
bool	isHitNearSegment (const CSCRecHit2D *h) const
bool	isSegmentGood (const ChamberHitContainer &rechitsInChamber) const
	Return true if segment is 'good'.
float	phiAtZ (float z) const
bool	replaceHit (const CSCRecHit2D *h, int layer)
void	tryAddingHitsToSegment (const ChamberHitContainer &rechitsInChamber, BoolContainer used, LayerIndex layerIndex, const ChamberHitContainerCIt i1, const ChamberHitContainerCIt i2)
	Try adding non-used hits to segment.
void	updateParameters (void)
AlgebraicSymMatrix	weightMatrix (void) const
Private Attributes
float	chi2Max
bool	debugInfo
float	dPhiFineMax
float	dPhiMax
float	dRPhiFineMax
float	dRPhiMax
int	minLayersApart
const std::string	myName
ChamberHitContainer	proto_segment
const CSCChamber *	theChamber
double	theChi2
LocalVector	theDirection
LocalPoint	theOrigin
float	uz
float	vz
float	wideSeg
float	windowScale

---

Detailed Description

This is the original algorithm for building endcap muon track segments out of the rechit's in a CSCChamber.

cf. CSCSegmentizerTC.
'SK' = 'Sasha Khanov' = Speed King

A CSCSegment is a RecSegment4D, and is built from CSCRecHit2D objects, each of which is a RecHit2DLocalPos.

This class is used by the CSCSegmentAlgorithm.
Alternative algorithms can be used for the segment building by writing classes like this, and then selecting which one is actually used via the CSCSegmentBuilder.

Original (in FORTRAN): Alexandre.Khanov@cern.ch
Ported to C++ and improved: Rick.Wilkinson@cern.ch
Reimplemented in terms of layer index, and bug fix: Tim.Cox@cern.ch
Ported to CMSSW 2006-04-03: Matteo.Sani@cern.ch

Date

2007/03/07 14:40:46

Revision

1.9

Author:

M. Sani

Definition at line 37 of file CSCSegAlgoSK.h.

---

Member Typedef Documentation

typedef std::deque<bool> CSCSegAlgoSK::BoolContainer

Definition at line 60 of file CSCSegAlgoSK.h.

typedef std::vector<const CSCRecHit2D*> CSCSegAlgoSK::ChamberHitContainer

Definition at line 52 of file CSCSegAlgoSK.h.

typedef std::vector<const CSCRecHit2D*>::const_iterator CSCSegAlgoSK::ChamberHitContainerCIt

Definition at line 53 of file CSCSegAlgoSK.h.

typedef std::vector<int> CSCSegAlgoSK::LayerIndex

Typedefs.

Definition at line 51 of file CSCSegAlgoSK.h.

---

Constructor & Destructor Documentation

CSCSegAlgoSK::CSCSegAlgoSK

(

const edm::ParameterSet &

ps

)

[explicit]

Constructor.

Definition at line 23 of file CSCSegAlgoSK.cc.

References chi2Max, debugInfo, dPhiFineMax, dPhiMax, dRPhiFineMax, dRPhiMax, lat::endl(), edm::ParameterSet::getParameter(), edm::ParameterSet::getUntrackedParameter(), LogDebug, minLayersApart, myName, and wideSeg.

                                                    : CSCSegmentAlgorithm(ps),
        myName("CSCSegAlgoSK") {
        
  debugInfo = ps.getUntrackedParameter<bool>("verboseInfo");
    
  dRPhiMax       = ps.getParameter<double>("dRPhiMax");
  dPhiMax        = ps.getParameter<double>("dPhiMax");
  dRPhiFineMax   = ps.getParameter<double>("dRPhiFineMax");
  dPhiFineMax    = ps.getParameter<double>("dPhiFineMax");
  chi2Max        = ps.getParameter<double>("chi2Max");
  wideSeg        = ps.getParameter<double>("wideSeg");
  minLayersApart = ps.getParameter<int>("minLayersApart");
        
  LogDebug("CSC") << myName << " has algorithm cuts set to: \n"
                  << "--------------------------------------------------------------------\n"
                  << "dRPhiMax     = " << dRPhiMax << '\n'
                  << "dPhiMax      = " << dPhiMax << '\n'
                  << "dRPhiFineMax = " << dRPhiFineMax << '\n'
                  << "dPhiFineMax  = " << dPhiFineMax << '\n'
                  << "chi2Max      = " << chi2Max << '\n'
                  << "wideSeg      = " << wideSeg << '\n'
                  << "minLayersApart = " << minLayersApart << std::endl;
}

virtual CSCSegAlgoSK::~CSCSegAlgoSK

(

)

[inline, virtual]

Destructor.

Definition at line 65 of file CSCSegAlgoSK.h.

{};

---

Member Function Documentation

bool CSCSegAlgoSK::addHit	(	const CSCRecHit2D *	hit,
		int	layer
	)			[private]

Utility functions.

Definition at line 377 of file CSCSegAlgoSK.cc.

References it, proto_segment, and updateParameters().

Referenced by buildSegments(), increaseProtoSegment(), and replaceHit().

                                                            {
  
  // Return true if hit was added successfully 
  // (and then parameters are updated).
  // Return false if there is already a hit on the same layer, or insert failed.
  
  ChamberHitContainer::const_iterator it;
  
  for(it = proto_segment.begin(); it != proto_segment.end(); it++)
    if (((*it)->cscDetId().layer() == layer) && (aHit != (*it)))
      return false; 
  
  proto_segment.push_back(aHit);
  updateParameters();
  
  return true;
}

bool CSCSegAlgoSK::areHitsCloseInGlobalPhi	(	const CSCRecHit2D *	h1,
		const CSCRecHit2D *	h2
	)			const [private]

Definition at line 260 of file CSCSegAlgoSK.cc.

References CSCRecHit2D::cscDetId(), dPhiMax, gp1, l1, l2, CSCDetId::layer(), CSCChamber::layer(), CSCRecHit2D::localPosition(), LogDebug, PV3DBase< T, PVType, FrameType >::phi(), theChamber, GeomDet::toGlobal(), and windowScale.

Referenced by buildSegments().

                                                                                             {
  
  const CSCLayer* l1 = theChamber->layer(h1->cscDetId().layer());
  GlobalPoint gp1 = l1->toGlobal(h1->localPosition());  
  const CSCLayer* l2 = theChamber->layer(h2->cscDetId().layer());
  GlobalPoint gp2 = l2->toGlobal(h2->localPosition());  
  
  float h1p = gp1.phi();
  float h2p = gp2.phi();
  float dphi12 = h1p - h2p;
  
  // Into range [-pi, pi) (phi() returns values in this range)
  if (dphi12 < -M_PI) 
    dphi12 += 2.*M_PI;  
  if (dphi12 >  M_PI) 
    dphi12 -= 2.*M_PI;
  LogDebug("CSC") << "    Hits at global phi= " << h1p << ", " 
                  << h2p << " have separation= " << dphi12;
  return (fabs(dphi12) < (dPhiMax * windowScale))? true:false;  // +v
}

bool CSCSegAlgoSK::areHitsCloseInLocalX	(	const CSCRecHit2D *	h1,
		const CSCRecHit2D *	h2
	)			const [private]

Utility functions.

Definition at line 251 of file CSCSegAlgoSK.cc.

References dRPhiMax, CSCRecHit2D::localPosition(), LogDebug, windowScale, PV3DBase< T, PVType, FrameType >::x(), and x.

Referenced by buildSegments().

                                                                                          {
  float h1x = h1->localPosition().x();
  float h2x = h2->localPosition().x();
  float deltaX = (h1->localPosition()-h2->localPosition()).x();
  LogDebug("CSC") << "    Hits at local x= " << h1x << ", " 
                  << h2x << " have separation= " << deltaX;
  return (fabs(deltaX) < (dRPhiMax * windowScale))? true:false;   // +v
}

std::vector< CSCSegment > CSCSegAlgoSK::buildSegments

(

ChamberHitContainer

rechits

)

Build track segments in this chamber (this is where the actual segment-building algorithm hides.

)

Definition at line 52 of file CSCSegAlgoSK.cc.

References funct::abs(), addHit(), areHitsCloseInGlobalPhi(), areHitsCloseInLocalX(), calculateError(), CSCChamberSpecs::chamberTypeName(), debugInfo, dumpHits(), HLT_VtxMuL3::errors, flagHitsAsUsed(), flipErrors(), gp1, h1, h2, i, i1, i2, isSegmentGood(), l1, l2, CSCChamber::layer(), CSCRecHit2D::localPosition(), LogDebug, minLayersApart, myName, GeomDet::position(), proto_segment, CSCChamber::specs(), pyDBSRunClass::temp, theChamber, theChi2, theDirection, theOrigin, GeomDet::toGlobal(), tryAddingHitsToSegment(), wideSeg, windowScale, and PV3DBase< T, PVType, FrameType >::z().

Referenced by run().

                                                                             {
        
  LogDebug("CSC") << "*********************************************";
  LogDebug("CSC") << "Start segment building in the new chamber: " << theChamber->specs()->chamberTypeName();
  LogDebug("CSC") << "*********************************************";
  
  
  LayerIndex layerIndex(rechits.size());
  
  for(unsigned int i = 0; i < rechits.size(); i++) {
    
    layerIndex[i] = rechits[i]->cscDetId().layer();
  }
  
  double z1 = theChamber->layer(1)->position().z();
  double z6 = theChamber->layer(6)->position().z();
  
  if ( z1 > 0. ) {
    if ( z1 > z6 ) { 
      reverse(layerIndex.begin(), layerIndex.end());
      reverse(rechits.begin(), rechits.end());
    }    
  }
  else if ( z1 < 0. ) {
    if ( z1 < z6 ) {
      reverse(layerIndex.begin(), layerIndex.end());
      reverse(rechits.begin(), rechits.end());
    }    
  }
  
  if (debugInfo) {
    // dump after sorting
    dumpHits(rechits);
  }
  
  if (rechits.size() < 2) {
    LogDebug("CSC") << myName << ": " << rechits.size() << 
      "  hit(s) in chamber is not enough to build a segment.\n";
    return std::vector<CSCSegment>(); 
  }
        
  // We have at least 2 hits. We intend to try all possible pairs of hits to start 
  // segment building. 'All possible' means each hit lies on different layers in the chamber.
  // BUT... once a hit has been assigned to a segment, we don't consider
  // it again.
  
  // Choose first hit (as close to IP as possible) h1 and 
  // second hit (as far from IP as possible) h2
  // To do this we iterate over hits in the chamber by layer - pick two layers.
  // @@ Require the two layers are at least 3 layers apart. May need tuning?
  // Then we iterate over hits within each of these layers and pick h1 and h2 from these.
  // If they are 'close enough' we build an empty segment.
  // Then try adding hits to this segment.
  
  // Initialize flags that a given hit has been allocated to a segment
  BoolContainer used(rechits.size(), false);
  
  // Define buffer for segments we build 
  std::vector<CSCSegment> segments;
  
  ChamberHitContainerCIt ib = rechits.begin();
  ChamberHitContainerCIt ie = rechits.end();
  
  // Possibly allow 2 passes, second widening scale factor for cuts
  windowScale = 1.; // scale factor for cuts
  
  int npass = (wideSeg > 1.)? 2 : 1;
  
  for (int ipass = 0; ipass < npass; ++ipass) {
    for (ChamberHitContainerCIt i1 = ib; i1 != ie; ++i1) {
      bool segok = false;
      if(used[i1-ib]) 
        continue;
      
      int layer1 = layerIndex[i1-ib]; //(*i1)->cscDetId().layer();
      const CSCRecHit2D* h1 = *i1;
      
      for (ChamberHitContainerCIt i2 = ie-1; i2 != i1; --i2) {
        if(used[i2-ib]) 
          continue;
        
        int layer2 = layerIndex[i2-ib]; //(*i2)->cscDetId().layer();
                                
        if (abs(layer2 - layer1) < minLayersApart) 
          break;
        const CSCRecHit2D* h2 = *i2;
        
        if (areHitsCloseInLocalX(h1, h2) && areHitsCloseInGlobalPhi(h1, h2)) {
          
          proto_segment.clear();
          
          const CSCLayer* l1 = theChamber->layer(layer1);
          GlobalPoint gp1 = l1->toGlobal(h1->localPosition());                                  
          const CSCLayer* l2 = theChamber->layer(layer2);
          GlobalPoint gp2 = l2->toGlobal(h2->localPosition());                                  
          LogDebug("CSC") << "start new segment from hits " << "h1: " 
                          << gp1 << " - h2: " << gp2 << "\n";
          
          if (!addHit(h1, layer1)) { 
            LogDebug("CSC") << "  failed to add hit h1\n";
            continue;
          }
          
          if (!addHit(h2, layer2)) { 
            LogDebug("CSC") << "  failed to add hit h2\n";
            continue;
          }
          
          tryAddingHitsToSegment(rechits, used, layerIndex, i1, i2); 
          
          // Check no. of hits on segment, and if enough flag them as used
          // and store the segment
          segok = isSegmentGood(rechits);
          if (segok) {
            flagHitsAsUsed(rechits, used);
            // Copy the proto_segment and its properties inside a CSCSegment.
            // Then fill the segment vector..
            
            if (proto_segment.empty()) {
              LogDebug("CSC") << "No segment has been found !!!\n";
            }   
            else {
              
              // calculate error matrix...
              AlgebraicSymMatrix errors = calculateError();

              // but reorder components to match what's required by TrackingRecHit interface
              // i.e. slopes first, then positions

              flipErrors( errors );

              CSCSegment temp(proto_segment, theOrigin, theDirection, errors, theChi2); 
              
              LogDebug("CSC") << "Found a segment !!!\n";
              segments.push_back(temp); 
            }
          }
        }  //   h1 & h2 close
        
        if (segok) 
          break;
      }  //  i2
    }  //  i1
    
    if (segments.size() > 1)  
      break;  // only change window if no segments found
    
    // Increase cut windows by factor of wideSeg
    windowScale = wideSeg;
    
  }  //  ipass
  
  // Give the segments to the CSCChamber
  return segments;
}

AlgebraicSymMatrix CSCSegAlgoSK::calculateError

(

void

)

const [private]

Definition at line 801 of file CSCSegAlgoSK.cc.

References funct::A, derivativeMatrix(), HLT_VtxMuL3::result, weightMatrix(), and weights.

Referenced by buildSegments().

                                                      {
  
  AlgebraicSymMatrix weights = weightMatrix();
  AlgebraicMatrix A = derivativeMatrix();
  
  // (AT W A)^-1
  // from https://www.phys.ufl.edu/~avery/fitting.html, part I
  int ierr;
  AlgebraicSymMatrix result = weights.similarityT(A);
  result.invert(ierr);
  
  // blithely assuming the inverting never fails...
  return result;
}

void CSCSegAlgoSK::compareProtoSegment	(	const CSCRecHit2D *	h,
		int	layer
	)			[private]

Definition at line 701 of file CSCSegAlgoSK.cc.

References LogDebug, proto_segment, replaceHit(), theChi2, theDirection, and theOrigin.

Referenced by tryAddingHitsToSegment().

                                                                      {
  
  // compare the chi2 of two segments
  double oldChi2 = theChi2;
  LocalPoint oldOrigin = theOrigin;
  LocalVector oldDirection = theDirection;
  ChamberHitContainer oldSegment = proto_segment;
  
  bool ok = replaceHit(h, layer);
  
  if (ok) {
    LogDebug("CSC") << "    hit in same layer as a hit on segment; try replacing old one..." 
                    << " chi2 new: " << theChi2 << " old: " << oldChi2 << "\n";
  }
  
  if ((theChi2 < oldChi2) && (ok)) {
    LogDebug("CSC")  << "    segment with replaced hit is better.\n";
  }
  else {
    proto_segment = oldSegment;
    theChi2 = oldChi2;
    theOrigin = oldOrigin;
    theDirection = oldDirection;
  }
}

HepMatrix CSCSegAlgoSK::derivativeMatrix

(

void

)

const [private]

Definition at line 754 of file CSCSegAlgoSK.cc.

References CSCRecHit2D::cscDetId(), it, CSCDetId::layer(), CSCChamber::layer(), CSCRecHit2D::localPosition(), lp, matrix, proto_segment, row, theChamber, GeomDet::toGlobal(), GeomDet::toLocal(), PV3DBase< T, PVType, FrameType >::z(), and z.

Referenced by calculateError().

                                               {
  
  ChamberHitContainer::const_iterator it;
  int nhits = proto_segment.size();
  HepMatrix matrix(2*nhits, 4);
  int row = 0;
  
  for(it = proto_segment.begin(); it != proto_segment.end(); ++it) {
    
    const CSCRecHit2D& hit = (**it);
    const CSCLayer* layer = theChamber->layer(hit.cscDetId().layer());
    GlobalPoint gp = layer->toGlobal(hit.localPosition());      
    LocalPoint lp = theChamber->toLocal(gp); 
    float z = lp.z();
    ++row;
    matrix(row, 1) = 1.;
    matrix(row, 3) = z;
    ++row;
    matrix(row, 2) = 1.;
    matrix(row, 4) = z;
  }
  return matrix;
}

void CSCSegAlgoSK::dumpHits

(

const ChamberHitContainer &

rechits

)

const [private]

Dump position and phi of each rechit in chamber after sort in z.

Definition at line 327 of file CSCSegAlgoSK.cc.

References gp1, it, l1, CSCChamber::layer(), PV3DBase< T, PVType, FrameType >::phi(), theChamber, and GeomDet::toGlobal().

Referenced by buildSegments().

                                                                    {
  
  // Dump positions of RecHit's in each CSCChamber
  ChamberHitContainerCIt it;
  edm::LogInfo("CSC") << "CSCChamber rechit dump.\n";   
  for(it=rechits.begin(); it!=rechits.end(); it++) {
    
    const CSCLayer* l1 = theChamber->layer((*it)->cscDetId().layer());
    GlobalPoint gp1 = l1->toGlobal((*it)->localPosition());     
    
    edm::LogInfo("CSC") << "Global pos.: " << gp1 << ", phi: " << gp1.phi() << ". Local position: "
                        << (*it)->localPosition() << ", phi: "
                        << (*it)->localPosition().phi() << ". Layer: "
                        << (*it)->cscDetId().layer() << "\n";
  }     
}

void CSCSegAlgoSK::fillChiSquared

(

void

)

[private]

Definition at line 607 of file CSCSegAlgoSK.cc.

References CSCRecHit2D::cscDetId(), CSCDetId::layer(), CSCChamber::layer(), CSCRecHit2D::localPosition(), CSCRecHit2D::localPositionError(), LogDebug, lp, proto_segment, theChamber, theChi2, theOrigin, GeomDet::toGlobal(), GeomDet::toLocal(), uz, vz, PV3DBase< T, PVType, FrameType >::x(), LocalError::xx(), LocalError::xy(), PV3DBase< T, PVType, FrameType >::y(), LocalError::yy(), and PV3DBase< T, PVType, FrameType >::z().

Referenced by updateParameters().

                                  {
  
  // The chi-squared is (m-Ap)T E (m-Ap)
  // where T denotes transpose.
  // This collapses to a simple sum over contributions from each
  // pair of measurements.
  float u0 = theOrigin.x();
  float v0 = theOrigin.y();
  double chsq = 0.;
  
  ChamberHitContainer::const_iterator ih;
  for (ih = proto_segment.begin(); ih != proto_segment.end(); ++ih) {
    
    const CSCRecHit2D& hit = (**ih);
    const CSCLayer* layer = theChamber->layer(hit.cscDetId().layer());
    GlobalPoint gp = layer->toGlobal(hit.localPosition());
    LocalPoint lp = theChamber->toLocal(gp);  // FIX !!
    
    double hu = lp.x();
    double hv = lp.y();
    double hz = lp.z();
    
    double du = u0 + uz * hz - hu;
    double dv = v0 + vz * hz - hv;
    
    HepMatrix IC(2,2);
    IC(1,1) = hit.localPositionError().xx();
    IC(1,2) = hit.localPositionError().xy();
    IC(2,1) = IC(1,2);
    IC(2,2) = hit.localPositionError().yy();
    
    // Invert covariance matrix
    int ierr = 0;
    IC.invert(ierr);
    if (ierr != 0) {
      LogDebug("CSC") << "CSCSegment::fillChiSquared: failed to invert covariance matrix=\n" << IC << "\n";
      
      // @@ NOW WHAT TO DO? Exception? Return? Ignore?
    }
    
    chsq += du*du*IC(1,1) + 2.*du*dv*IC(1,2) + dv*dv*IC(2,2);
  }
  theChi2 = chsq;
}

void CSCSegAlgoSK::fillLocalDirection

(

void

)

[private]

Always enforce direction of segment to point from IP outwards (Incorrect for particles not coming from IP, of course.

)

Definition at line 652 of file CSCSegAlgoSK.cc.

References funct::sqrt(), theChamber, theDirection, theOrigin, GeomDet::toGlobal(), uz, vz, and z.

Referenced by updateParameters().

                                      {
  // Always enforce direction of segment to point from IP outwards
  // (Incorrect for particles not coming from IP, of course.)
  
  double dxdz = uz;
  double dydz = vz;
  double dz = 1./sqrt(1. + dxdz*dxdz + dydz*dydz);
  double dx = dz*dxdz;
  double dy = dz*dydz;
  LocalVector localDir(dx,dy,dz);
  
  // localDir may need sign flip to ensure it points outward from IP
  // ptc: Examine its direction and origin in global z: to point outward
  // the localDir should always have same sign as global z...
  
  double globalZpos = ( theChamber->toGlobal( theOrigin ) ).z();
  double globalZdir = ( theChamber->toGlobal( localDir ) ).z();
  double directionSign = globalZpos * globalZdir;
  
  theDirection = (directionSign * localDir).unit();
  
}

void CSCSegAlgoSK::fitSlopes

(

void

)

[private]

Definition at line 455 of file CSCSegAlgoSK.cc.

References CSCRecHit2D::cscDetId(), CSCDetId::layer(), CSCChamber::layer(), CSCRecHit2D::localPosition(), CSCRecHit2D::localPositionError(), LogDebug, lp, p, proto_segment, solve(), theChamber, theOrigin, GeomDet::toGlobal(), GeomDet::toLocal(), uz, v, vz, PV3DBase< T, PVType, FrameType >::x(), LocalError::xx(), LocalError::xy(), PV3DBase< T, PVType, FrameType >::y(), LocalError::yy(), PV3DBase< T, PVType, FrameType >::z(), and z.

Referenced by updateParameters().

                             {
  
  // Update parameters of fit
  // ptc 13-Aug-02: This does a linear least-squares fit
  // to the hits associated with the segment, in the z projection.
  
  // In principle perhaps one could fit the strip and wire
  // measurements (u, v respectively), to
  // u = u0 + uz * z
  // v = v0 + vz * z
  // where u0, uz, v0, vz are the parameters resulting from the fit.
  // But what is actually done is fit to the local x, y coordinates 
  // of the RecHits. However the strip measurement controls the precision
  // of x, and the wire measurement controls that of y.
  // Precision in local coordinate:
  //       u (strip, sigma~200um), v (wire, sigma~1cm)
  
  // I have verified that this code agrees with the formulation given
  // on p246-247 of 'Data analysis techniques for high-energy physics
  // experiments' by Bock, Grote, Notz & Regler, and that on p111-113
  // of 'Statistics' by Barlow.
  
  // Formulate the matrix equation representing the least-squares fit
  // We have a vector of measurements m, which is a 2n x 1 dim matrix
  // The transpose mT is (u1, v1, u2, v2, ..., un, vn)
  // where ui is the strip-associated measurement and vi is the
  // wire-associated measurement for a given RecHit i.
  // The fit is to
  // u = u0 + uz * z
  // v = v0 + vz * z
  // where u0, uz, v0, vz are the parameters to be obtained from the fit.
  // These are contained in a vector p which is a 4x1 dim matrix, and
  // its transpose pT is (u0, v0, uz, vz). Note the ordering!
  // The covariance matrix for each pair of measurements is 2 x 2 and
  // the inverse of this is the error matrix E.
  // The error matrix for the whole set of n measurements is a diagonal
  // matrix with diagonal elements the individual 2 x 2 error matrices
  // (because the inverse of a diagonal matrix is a diagonal matrix
  // with each element the inverse of the original.)
  
  // The matrix 'matrix' in method 'CSCSegment::weightMatrix()' is this 
  // block-diagonal overall covariance matrix. It is inverted to the 
  // block-diagonal error matrix right before it is returned.
  
  // Use the matrix A defined by
  //    1   0   z1  0
  //    0   1   0   z1
  //    1   0   z2  0
  //    0   1   0   z2
  //    ..  ..  ..  ..
  //    1   0   zn  0
  //    0   1   0   zn
  
  // The matrix A is returned by 'CSCSegment::derivativeMatrix()'.
  
  // Then the normal equations are encapsulated in the matrix equation
  //
  //    (AT E A)p = (AT E)m
  //
  // where AT is the transpose of A.
  // We'll call the combined matrix on the LHS, M, and that on the RHS, B:
  //     M p = B
  
  // We solve this for the parameter vector, p.
  // The elements of M and B then involve sums over the hits
  
  // The error matrix of the parameters is obtained by 
  // (AT E A)^-1 calculated in 'calculateError()'.
  
  // The 4 values in p can be accessed from 'CSCSegment::parameters()'
  // in the order uz, vz, u0, v0.
  
  // NOTE 1
  // Do the #hits = 2 case separately.
  // (I hope they're not on the same layer! They should not be, by construction.)
  
  // NOTE 2
  // We need local position of a RecHit w.r.t. the CHAMBER
  // and the RecHit itself only knows its local position w.r.t.
  // the LAYER, so we must explicitly transform global position.
  
  HepMatrix M(4,4,0);
  HepVector B(4,0);
  
  ChamberHitContainer::const_iterator ih = proto_segment.begin();
  
  for (ih = proto_segment.begin(); ih != proto_segment.end(); ++ih) {
    
    const CSCRecHit2D& hit = (**ih);
    const CSCLayer* layer = theChamber->layer(hit.cscDetId().layer());
    GlobalPoint gp = layer->toGlobal(hit.localPosition());
    LocalPoint  lp  = theChamber->toLocal(gp); 
    
    // ptc: Local position of hit w.r.t. chamber
    double u = lp.x();
    double v = lp.y();
    double z = lp.z();
    
    // ptc: Covariance matrix of local errors 
    HepMatrix IC(2,2);
    IC(1,1) = hit.localPositionError().xx();
    IC(1,2) = hit.localPositionError().xy();
    IC(2,1) = IC(1,2); // since Cov is symmetric
    IC(2,2) = hit.localPositionError().yy();
    
    // ptc: Invert covariance matrix (and trap if it fails!)
    int ierr = 0;
    IC.invert(ierr); // inverts in place
    if (ierr != 0) {
      LogDebug("CSC") << "CSCSegment::fitSlopes: failed to invert covariance matrix=\n" << IC << "\n";
      
      //@@ NOW WHAT TO DO? Exception? Return? Ignore?
      //@@ Implement throw
    }
    
    // ptc: Note that IC is no longer Cov but Cov^-1
    M(1,1) += IC(1,1);
    M(1,2) += IC(1,2);
    M(1,3) += IC(1,1) * z;
    M(1,4) += IC(1,2) * z;
    B(1) += u * IC(1,1) + v * IC(1,2);
    
    M(2,1) += IC(2,1);
    M(2,2) += IC(2,2);
    M(2,3) += IC(2,1) * z;
    M(2,4) += IC(2,2) * z;
    B(2) += u * IC(2,1) + v * IC(2,2);
    
    M(3,1) += IC(1,1) * z;
    M(3,2) += IC(1,2) * z;
    M(3,3) += IC(1,1) * z * z;
    M(3,4) += IC(1,2) * z * z;
    B(3) += ( u * IC(1,1) + v * IC(1,2) ) * z;
    
    M(4,1) += IC(2,1) * z;
    M(4,2) += IC(2,2) * z;
    M(4,3) += IC(2,1) * z * z;
    M(4,4) += IC(2,2) * z * z;
    B(4) += ( u * IC(2,1) + v * IC(2,2) ) * z;
  }
  
  // Solve the matrix equation using CLHEP's 'solve'
  //@@ ptc: CAN solve FAIL?? UNCLEAR FROM (LACK OF) CLHEP DOC
  HepVector p = solve(M, B);
  
  // Update member variables uz, vz, theOrigin
  // Note it has local z = 0
  theOrigin = LocalPoint(p(1), p(2), 0.);
  uz = p(3);
  vz = p(4);
}

void CSCSegAlgoSK::flagHitsAsUsed	(	const ChamberHitContainer &	rechitsInChamber,
		BoolContainer &	used
	)			const [private]

Flag hits on segment as used.

Definition at line 362 of file CSCSegAlgoSK.cc.

References proto_segment.

Referenced by buildSegments().

                                                              {
  
  // Flag hits on segment as used
  ChamberHitContainerCIt ib = rechitsInChamber.begin();
  ChamberHitContainerCIt hi, iu;
  
  for(hi = proto_segment.begin(); hi != proto_segment.end(); ++hi) {
    for(iu = ib; iu != rechitsInChamber.end(); ++iu) {
      if(*hi == *iu)
        used[iu-ib] = true;
    }
  }
}

void CSCSegAlgoSK::flipErrors

(

AlgebraicSymMatrix &

a

)

const [private]

Definition at line 816 of file CSCSegAlgoSK.cc.

References a.

Referenced by buildSegments().

                                                           {

  // The CSCSegment needs the error matrix re-arranged

  AlgebraicSymMatrix hold( a );

  // errors on slopes into upper left
  a(1,1) = hold(3,3);
  a(1,2) = hold(3,4);
  a(2,1) = hold(4,3);
  a(2,2) = hold(4,4);
  
  // errors on positions into lower right
  a(3,3) = hold(1,1);
  a(3,4) = hold(1,2);
  a(4,3) = hold(2,1);
  a(4,4) = hold(2,2);

  // off-diagonal elements remain unchanged

}

bool CSCSegAlgoSK::hasHitOnLayer

(

int

layer

)

const [private]

Definition at line 675 of file CSCSegAlgoSK.cc.

References it, and proto_segment.

Referenced by tryAddingHitsToSegment().

                                                {
  
  // Is there is already a hit on this layer?
  ChamberHitContainerCIt it;
  
  for(it = proto_segment.begin(); it != proto_segment.end(); it++)
    if ((*it)->cscDetId().layer() == layer)
      return true; 
  
  return false;
}

void CSCSegAlgoSK::increaseProtoSegment	(	const CSCRecHit2D *	h,
		int	layer
	)			[private]

Definition at line 727 of file CSCSegAlgoSK.cc.

References addHit(), chi2Max, LogDebug, proto_segment, theChi2, theDirection, and theOrigin.

Referenced by tryAddingHitsToSegment().

                                                                       {
  
  double oldChi2 = theChi2;
  LocalPoint oldOrigin = theOrigin;
  LocalVector oldDirection = theDirection;
  ChamberHitContainer oldSegment = proto_segment;
  
  bool ok = addHit(h, layer);
  
  if (ok) {
    LogDebug("CSC") << "    hit in new layer: added to segment, new chi2: " 
                    << theChi2 << "\n";
  }
  
  int ndf = 2*proto_segment.size() - 4;
  
  if (ok && ((ndf <= 0) || (theChi2/ndf < chi2Max))) {
    LogDebug("CSC") << "    segment with added hit is good.\n" ;                // FIX
  }     
  else {
    proto_segment = oldSegment;
    theChi2 = oldChi2;
    theOrigin = oldOrigin;
    theDirection = oldDirection;
  }                     
}               

bool CSCSegAlgoSK::isHitNearSegment

(

const CSCRecHit2D *

h

)

const [private]

Definition at line 281 of file CSCSegAlgoSK.cc.

References CSCRecHit2D::cscDetId(), dPhiFineMax, dRPhiFineMax, l1, CSCDetId::layer(), CSCChamber::layer(), CSCRecHit2D::localPosition(), LogDebug, PV3DBase< T, PVType, FrameType >::perp(), PV3DBase< T, PVType, FrameType >::phi(), phiAtZ(), theChamber, GeomDet::toGlobal(), windowScale, and PV3DBase< T, PVType, FrameType >::z().

Referenced by tryAddingHitsToSegment().

                                                              {
  
  // Is hit near segment? 
  // Requires deltaphi and rxy*deltaphi within ranges specified
  // in parameter set, where rxy=sqrt(x**2+y**2) of hit itself.
  // Note that to make intuitive cuts on delta(phi) one must work in
  // phi range (-pi, +pi] not [0, 2pi)
  
  const CSCLayer* l1 = theChamber->layer(h->cscDetId().layer());
  GlobalPoint hp = l1->toGlobal(h->localPosition());    
  
  float hphi = hp.phi();          // in (-pi, +pi]
  if (hphi < 0.) 
    hphi += 2.*M_PI;            // into range [0, 2pi)
  float sphi = phiAtZ(hp.z());    // in [0, 2*pi)
  float phidif = sphi-hphi;
  if (phidif < 0.) 
    phidif += 2.*M_PI;          // into range [0, 2pi)
  if (phidif > M_PI) 
    phidif -= 2.*M_PI;          // into range (-pi, pi]
  
  float dRPhi = fabs(phidif)*hp.perp();
  LogDebug("CSC") << "    is hit at phi_h= " << hphi << " near segment phi_seg= " << sphi 
                  << "? is " << dRPhi << "<" << dRPhiFineMax*windowScale << " ? " 
                  << " and is |" << phidif << "|<" << dPhiFineMax*windowScale << " ?";
  
  return ((dRPhi < dRPhiFineMax*windowScale) && 
          (fabs(phidif) < dPhiFineMax*windowScale))? true:false;  // +v
}

bool CSCSegAlgoSK::isSegmentGood

(

const ChamberHitContainer &

rechitsInChamber

)

const [private]

Return true if segment is 'good'.

In this algorithm, 'good' means has sufficient hits

Definition at line 344 of file CSCSegAlgoSK.cc.

References proto_segment, and windowScale.

Referenced by buildSegments().

                                                                                  {
  
  // If the chamber has 20 hits or fewer, require at least 3 hits on segment
  // If the chamber has >20 hits require at least 4 hits
  //@@ THESE VALUES SHOULD BECOME PARAMETERS?
  bool ok = false;
  
  unsigned int iadd = ( rechitsInChamber.size() > 20 )? iadd = 1 : 0;  
  
  if (windowScale > 1.)
    iadd = 1;
  
  if (proto_segment.size() >= 3+iadd)
    ok = true;
  
  return ok;
}

float CSCSegAlgoSK::phiAtZ

(

float

z

)

const [private]

Definition at line 311 of file CSCSegAlgoSK.cc.

References f, l1, CSCChamber::layer(), phi, proto_segment, theChamber, theDirection, theOrigin, GeomDet::toGlobal(), PV3DBase< T, PVType, FrameType >::x(), x, PV3DBase< T, PVType, FrameType >::y(), y, and PV3DBase< T, PVType, FrameType >::z().

Referenced by isHitNearSegment().

                                        {
  
  // Returns a phi in [ 0, 2*pi )
  const CSCLayer* l1 = theChamber->layer((*(proto_segment.begin()))->cscDetId().layer());
  GlobalPoint gp = l1->toGlobal(theOrigin);     
  GlobalVector gv = l1->toGlobal(theDirection); 
  
  float x = gp.x() + (gv.x()/gv.z())*(z - gp.z());
  float y = gp.y() + (gv.y()/gv.z())*(z - gp.z());
  float phi = atan2(y, x);
  if (phi < 0.f ) 
    phi += 2. * M_PI;
  
  return phi ;
}

bool CSCSegAlgoSK::replaceHit	(	const CSCRecHit2D *	h,
		int	layer
	)			[private]

Definition at line 687 of file CSCSegAlgoSK.cc.

References addHit(), it, and proto_segment.

Referenced by compareProtoSegment().

                                                             {
  
  // replace a hit from a layer 
  ChamberHitContainer::iterator it;
  for (it = proto_segment.begin(); it != proto_segment.end();) {
    if ((*it)->cscDetId().layer() == layer)
      it = proto_segment.erase(it);
    else
      ++it;   
  }
  
  return addHit(h, layer);                                  
}

std::vector< CSCSegment > CSCSegAlgoSK::run	(	const CSCChamber *	aChamber,
		ChamberHitContainer	rechits
	)

Here we must implement the algorithm.

Definition at line 47 of file CSCSegAlgoSK.cc.

References buildSegments(), and theChamber.

                                                                                               {
    theChamber = aChamber; 
    return buildSegments(rechits); 
}

void CSCSegAlgoSK::tryAddingHitsToSegment	(	const ChamberHitContainer &	rechitsInChamber,
		BoolContainer	used,
		LayerIndex	layerIndex,
		const ChamberHitContainerCIt	i1,
		const ChamberHitContainerCIt	i2
	)			[private]

Try adding non-used hits to segment.

Definition at line 208 of file CSCSegAlgoSK.cc.

References compareProtoSegment(), gp1, h, hasHitOnLayer(), i, increaseProtoSegment(), isHitNearSegment(), CSCChamber::layer(), CSCRecHit2D::localPosition(), LogDebug, proto_segment, theChamber, and GeomDet::toGlobal().

Referenced by buildSegments().

                                                                                                            {

  // Iterate over the layers with hits in the chamber
  // Skip the layers containing the segment endpoints
  // Test each hit on the other layers to see if it is near the segment
  // If it is, see whether there is already a hit on the segment from the same layer
  //    - if so, and there are more than 2 hits on the segment, copy the segment,
  //      replace the old hit with the new hit. If the new segment chi2 is better
  //      then replace the original segment with the new one (by swap)
  //    - if not, copy the segment, add the hit. If the new chi2/dof is still satisfactory
  //      then replace the original segment with the new one (by swap)
  
  ChamberHitContainerCIt ib = rechits.begin();
  ChamberHitContainerCIt ie = rechits.end();
  
  for (ChamberHitContainerCIt i = ib; i != ie; ++i) {
    if (i == i1 || i == i2 || used[i-ib]) 
      continue; 
    
    int layer = layerIndex[i-ib]; 
    const CSCRecHit2D* h = *i;
    if (isHitNearSegment(h)) {
      
      GlobalPoint gp1 = theChamber->layer(layer)->toGlobal(h->localPosition());         
      LogDebug("CSC") << "    hit at global " << gp1 << " is near segment\n.";
      
      // Don't consider alternate hits on layers holding the two starting points
      if (hasHitOnLayer(layer)) {
        if (proto_segment.size() <= 2) {
          LogDebug("CSC") << "    " << proto_segment.size() 
                          << " hits on segment...skip hit on same layer.\n";
          continue;
        }
        compareProtoSegment(h, layer);
      } 
      else                      
        increaseProtoSegment(h, layer);
    }   // h & seg close
  }   // i
}

void CSCSegAlgoSK::updateParameters

(

void

)

[private]

Definition at line 395 of file CSCSegAlgoSK.cc.

References fillChiSquared(), fillLocalDirection(), fitSlopes(), h1, h2, CSCChamber::layer(), CSCRecHit2D::localPosition(), proto_segment, theChamber, theChi2, theOrigin, GeomDet::toGlobal(), GeomDet::toLocal(), uz, vz, PV3DBase< T, PVType, FrameType >::x(), PV3DBase< T, PVType, FrameType >::y(), and PV3DBase< T, PVType, FrameType >::z().

Referenced by addHit().

                                    {
  
  // Note that we need local position of a RecHit w.r.t. the CHAMBER
  // and the RecHit itself only knows its local position w.r.t.
  // the LAYER, so need to explicitly transform to global position.
  
  //  no. of hits in the RecHitsOnSegment
  //  By construction this is the no. of layers with hits
  //  since we allow just one hit per layer in a segment.
  
  int nh = proto_segment.size();
  
  // First hit added to a segment must always fail here
  if (nh < 2) 
    return;
  
  if (nh == 2) {
    
    // Once we have two hits we can calculate a straight line 
    // (or rather, a straight line for each projection in xz and yz.)
    ChamberHitContainer::const_iterator ih = proto_segment.begin();
    int il1 = (*ih)->cscDetId().layer();
    const CSCRecHit2D& h1 = (**ih);
    ++ih;    
    int il2 = (*ih)->cscDetId().layer();
    const CSCRecHit2D& h2 = (**ih);
    
    //@@ Skip if on same layer, but should be impossible
    if (il1 == il2) 
      return;
    
    const CSCLayer* layer1 = theChamber->layer(il1);
    const CSCLayer* layer2 = theChamber->layer(il2);
    
    GlobalPoint h1glopos = layer1->toGlobal(h1.localPosition());
    GlobalPoint h2glopos = layer2->toGlobal(h2.localPosition());
    
    // localPosition is position of hit wrt layer (so local z = 0)
    theOrigin = h1.localPosition();
    
    // We want hit wrt chamber (and local z will be != 0)
    LocalPoint h1pos = theChamber->toLocal(h1glopos);  
    LocalPoint h2pos = theChamber->toLocal(h2glopos);  
    
    float dz = h2pos.z()-h1pos.z();
    uz = (h2pos.x()-h1pos.x())/dz ;
    vz = (h2pos.y()-h1pos.y())/dz ;
    
    theChi2 = 0.;
  }
  else if (nh > 2) {
    
    // When we have more than two hits then we can fit projections to straight lines
    fitSlopes();  
    fillChiSquared();
  } // end of 'if' testing no. of hits
  
  fillLocalDirection(); 
}

AlgebraicSymMatrix CSCSegAlgoSK::weightMatrix

(

void

)

const [private]

Definition at line 779 of file CSCSegAlgoSK.cc.

References it, CSCRecHit2D::localPositionError(), matrix, proto_segment, row, LocalError::xx(), LocalError::xy(), and LocalError::yy().

Referenced by calculateError().

                                                    {
  
  std::vector<const CSCRecHit2D*>::const_iterator it;
  int nhits = proto_segment.size();
  AlgebraicSymMatrix matrix(2*nhits, 0);
  int row = 0;
  
  for (it = proto_segment.begin(); it != proto_segment.end(); ++it) {
    
    const CSCRecHit2D& hit = (**it);
    ++row;
    matrix(row, row)   = hit.localPositionError().xx();
    matrix(row, row+1) = hit.localPositionError().xy();
    ++row;
    matrix(row, row-1) = hit.localPositionError().xy();
    matrix(row, row)   = hit.localPositionError().yy();
  }
  int ierr;
  matrix.invert(ierr);
  return matrix;
}

---

Member Data Documentation

float CSCSegAlgoSK::chi2Max [private]

Definition at line 146 of file CSCSegAlgoSK.h.

Referenced by CSCSegAlgoSK(), and increaseProtoSegment().

bool CSCSegAlgoSK::debugInfo [private]

Definition at line 149 of file CSCSegAlgoSK.h.

Referenced by buildSegments(), and CSCSegAlgoSK().

float CSCSegAlgoSK::dPhiFineMax [private]

Definition at line 145 of file CSCSegAlgoSK.h.

Referenced by CSCSegAlgoSK(), and isHitNearSegment().

float CSCSegAlgoSK::dPhiMax [private]

Definition at line 143 of file CSCSegAlgoSK.h.

Referenced by areHitsCloseInGlobalPhi(), and CSCSegAlgoSK().

float CSCSegAlgoSK::dRPhiFineMax [private]

Definition at line 144 of file CSCSegAlgoSK.h.

Referenced by CSCSegAlgoSK(), and isHitNearSegment().

float CSCSegAlgoSK::dRPhiMax [private]

Definition at line 142 of file CSCSegAlgoSK.h.

Referenced by areHitsCloseInLocalX(), and CSCSegAlgoSK().

int CSCSegAlgoSK::minLayersApart [private]

Definition at line 148 of file CSCSegAlgoSK.h.

Referenced by buildSegments(), and CSCSegAlgoSK().

const std::string CSCSegAlgoSK::myName [private]

Definition at line 135 of file CSCSegAlgoSK.h.

Referenced by buildSegments(), and CSCSegAlgoSK().

ChamberHitContainer CSCSegAlgoSK::proto_segment [private]

Definition at line 134 of file CSCSegAlgoSK.h.

Referenced by addHit(), buildSegments(), compareProtoSegment(), derivativeMatrix(), fillChiSquared(), fitSlopes(), flagHitsAsUsed(), hasHitOnLayer(), increaseProtoSegment(), isSegmentGood(), phiAtZ(), replaceHit(), tryAddingHitsToSegment(), updateParameters(), and weightMatrix().

const CSCChamber* CSCSegAlgoSK::theChamber [private]

Definition at line 133 of file CSCSegAlgoSK.h.

Referenced by areHitsCloseInGlobalPhi(), buildSegments(), derivativeMatrix(), dumpHits(), fillChiSquared(), fillLocalDirection(), fitSlopes(), isHitNearSegment(), phiAtZ(), run(), tryAddingHitsToSegment(), and updateParameters().

double CSCSegAlgoSK::theChi2 [private]

Definition at line 137 of file CSCSegAlgoSK.h.

Referenced by buildSegments(), compareProtoSegment(), fillChiSquared(), increaseProtoSegment(), and updateParameters().

LocalVector CSCSegAlgoSK::theDirection [private]

Definition at line 139 of file CSCSegAlgoSK.h.

Referenced by buildSegments(), compareProtoSegment(), fillLocalDirection(), increaseProtoSegment(), and phiAtZ().

LocalPoint CSCSegAlgoSK::theOrigin [private]

Definition at line 138 of file CSCSegAlgoSK.h.

Referenced by buildSegments(), compareProtoSegment(), fillChiSquared(), fillLocalDirection(), fitSlopes(), increaseProtoSegment(), phiAtZ(), and updateParameters().

float CSCSegAlgoSK::uz [private]

Definition at line 140 of file CSCSegAlgoSK.h.

Referenced by fillChiSquared(), fillLocalDirection(), fitSlopes(), and updateParameters().

float CSCSegAlgoSK::vz [private]

Definition at line 140 of file CSCSegAlgoSK.h.

Referenced by fillChiSquared(), fillLocalDirection(), fitSlopes(), and updateParameters().

float CSCSegAlgoSK::wideSeg [private]

Definition at line 147 of file CSCSegAlgoSK.h.

Referenced by buildSegments(), and CSCSegAlgoSK().

float CSCSegAlgoSK::windowScale [private]

Definition at line 141 of file CSCSegAlgoSK.h.

Referenced by areHitsCloseInGlobalPhi(), areHitsCloseInLocalX(), buildSegments(), isHitNearSegment(), and isSegmentGood().

---

The documentation for this class was generated from the following files:

• RecoLocalMuon/CSCSegment/src/CSCSegAlgoSK.h
• RecoLocalMuon/CSCSegment/src/CSCSegAlgoSK.cc

---