CSCSegFit.h

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#ifndef CSCSegment_CSCSegFit_h
#define CSCSegment_CSCSegFit_h

// CSCSegFit.h  - Segment fitting factored out of CSC segment builders - Tim Cox
// Last mod: 03.02.2015

/* This as an object which is initialized by a set of rechits (2 to 6) in a 
 * specific CSC 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 CSC. This means maximum dimensions
 * can be specified at compile time and hence satisfies SMatrix constraints.
 * 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/CSCRecHit/interface/CSCRecHit2D.h>
#include <Geometry/CSCGeometry/interface/CSCChamber.h>

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

#include <vector>

class CSCSegFit {
public:
  // TYPES

  typedef std::vector<const CSCRecHit2D*> CSCSetOfHits;

  // 12 x12 Symmetric
  typedef ROOT::Math::SMatrix<double, 12, 12, ROOT::Math::MatRepSym<double, 12> > SMatrixSym12;

  // 12 x 4
  typedef ROOT::Math::SMatrix<double, 12, 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
  CSCSegFit(const CSCChamber* csc, CSCSetOfHits hits)
      : chamber_(csc), hits_(hits), scaleXError_(1.0), fitdone_(false) {}

  virtual ~CSCSegFit() {}

  // Least-squares fit
  void 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
  CSCSetOfHits 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_; }
  const CSCChamber* chamber() const { return chamber_; }
  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

  const CSCChamber* chamber_;
  CSCSetOfHits 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