MuonSegFit.h

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#ifndef GEMSegment_MuonSegFit_h
#define GEMSegment_MuonSegFit_h

// MuonSegFit.h - Segment fitting factored out of MuonRecHit segment builder based on
// CSCSegFit.h  - Segment fitting factored out of CSC segment builders - Tim Cox
// Last mod: 15.04.2016 Jason Lee

/* This as an object which is initialized by a set of rechits (2 to 6) in a 
 * specific MuonRecHit and has the functionality to make a least squares fit 
 * to a straight line in 2-dim for those rechits.
 * The covariance matrix and chi2 of the fit are calculated.
 * The original code made use of CLHEP matrices but this version uses 
 * ROOT SMatrices because they are  multithreading compatible.
 * Because of this, the no. of rechits that can be handled is limited to
 * a maximum of 6, one per layer of a Muon chamber. This means maximum dimensions
 * can be specified at compile time and hence satisfies SMatrix constraints.
 * This means that if at a later stage we would change the geometry to have
 * for instance 10 detection layers, we will have to modify this code too.
 * For 2 hits of course there is no fit - just draw a straight line between them.
 * Details of the algorithm are in the .cc file
 *
 */

#include "DataFormats/TrackingRecHit/interface/TrackingRecHit.h"

#include "FWCore/MessageLogger/interface/MessageLogger.h"

#include <Math/Functions.h>
#include <Math/SVector.h>
#include <Math/SMatrix.h>

#include <vector>

class MuonSegFit {
public:
  // TYPES
  //typedef std::vector<const TrackingRecHit*> MuonRecHitContainer;
  typedef std::shared_ptr<TrackingRecHit> MuonRecHitPtr;
  typedef std::vector<MuonRecHitPtr> MuonRecHitContainer;

  static const int MaxHits2 = 22;  // maxHit2 = 2*max hits
  // 12 x12 Symmetric
  typedef ROOT::Math::SMatrix<double, MaxHits2, MaxHits2, ROOT::Math::MatRepSym<double, MaxHits2> > SMatrixSym12;

  // 12 x 4
  typedef ROOT::Math::SMatrix<double, MaxHits2, 4> SMatrix12by4;

  // 4 x 4 General + Symmetric
  typedef ROOT::Math::SMatrix<double, 4> SMatrix4;
  typedef ROOT::Math::SMatrix<double, 4, 4, ROOT::Math::MatRepSym<double, 4> > SMatrixSym4;

  // 2 x 2 Symmetric
  typedef ROOT::Math::SMatrix<double, 2, 2, ROOT::Math::MatRepSym<double, 2> > SMatrixSym2;

  // 4-dim vector
  typedef ROOT::Math::SVector<double, 4> SVector4;

  // PUBLIC FUNCTIONS

  //@@ WANT OBJECT TO CACHE THE SET OF HITS SO CANNOT PASS BY REF
  // NOTE - We need local position of a RecHit w.r.t. the CHAMBER
  MuonSegFit(MuonRecHitContainer hits)
      : hits_(hits), uslope_(.0), vslope_(.0), chi2_(.0), ndof_(0), scaleXError_(1.0), fitdone_(false) {}

  virtual ~MuonSegFit() {}

  // Least-squares fit
  bool fit(void);  // fill uslope_, vslope_, intercept_  @@ FKA fitSlopes()
  // Calculate covariance matrix of fitted parameters
  AlgebraicSymMatrix covarianceMatrix(void);

  // Change scale factor of rechit x error
  // - expert use only!
  void setScaleXError(double factor) { scaleXError_ = factor; }

  // Fit values
  float xfit(float z) const;
  float yfit(float z) const;

  // Deviations from fit for given input (local w.r.t. chamber)
  float xdev(float x, float z) const;
  float ydev(float y, float z) const;
  float Rdev(float x, float y, float z) const;

  // Other public functions are accessors
  MuonRecHitContainer hits(void) const { return hits_; }
  double scaleXError(void) const { return scaleXError_; }
  size_t nhits(void) const { return hits_.size(); }
  double chi2(void) const { return chi2_; }
  int ndof(void) const { return ndof_; }
  LocalPoint intercept() const { return intercept_; }
  LocalVector localdir() const { return localdir_; }
  bool fitdone() const { return fitdone_; }

private:
  // PRIVATE FUNCTIONS

  void fit2(void);     // fit for 2 hits
  void fitlsq(void);   // least-squares fit for 3-6 hits
  void setChi2(void);  // fill chi2_ & ndof_ @@ FKA fillChiSquared()

protected:
  // PROTECTED FUNCTIONS - derived class needs access

  // Set segment direction 'out' from IP
  void setOutFromIP(void);  // fill localdir_  @@ FKA fillLocalDirection()

  SMatrix12by4 derivativeMatrix(void);
  SMatrixSym12 weightMatrix(void);
  AlgebraicSymMatrix flipErrors(const SMatrixSym4&);

  // PROTECTED MEMBER VARIABLES - derived class needs access

  MuonRecHitContainer hits_;  //@@ FKA protoSegment
  float uslope_;              //@@ FKA protoSlope_u
  float vslope_;              //@@ FKA protoSlope_v
  LocalPoint intercept_;      //@@ FKA protoIntercept
  LocalVector localdir_;      //@@ FKA protoDirection
  double chi2_;               //@@ FKA protoChi2
  int ndof_;                  //@@ FKA protoNDF, which was double!!
  double scaleXError_;
  bool fitdone_;
};

#endif