ParabolaFit.h

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#ifndef ParabolaFit_H
#define ParabolaFit_H

#include <vector>

class ParabolaFit {
public:
  struct Result { double parA, parB, parC; 
                  double varAA, varBB, varCC, varAB, varAC, varBC; } ;
  ParabolaFit() : 
      doErr(true), hasFixedParC(false), hasValues(false), hasErrors(false), hasWeights(true) { }

  void addPoint(double x, double y);
  void addPoint(double x, double y, double weight);

  void skipErrorCalculationByDefault() { doErr = false; }
  void fixParC(double val) { hasFixedParC = true; theResult.parC = val; }

  const Result & result(bool doErrors) const;

  double parA() const  { if(!hasValues) result(doErr); return theResult.parA; }
  double parB() const  { if(!hasValues) result(doErr); return theResult.parB; }
  double parC() const  { if(!hasValues) result(doErr); return theResult.parC; }
  double varAA() const { if(!hasErrors) result(true); return theResult.varAA; }
  double varBB() const { if(!hasErrors) result(true); return theResult.varBB; }
  double varCC() const { if(!hasErrors) result(true); return theResult.varCC; }
  double varAB() const { if(!hasErrors) result(true); return theResult.varAB; }
  double varAC() const { if(!hasErrors) result(true); return theResult.varAC; }
  double varBC() const { if(!hasErrors) result(true); return theResult.varBC; }

  double chi2() const;
  int    dof() const;

private:
  struct Column { double r1; double r2; double r3; };
  double det(const Column & c1, const Column & c2, const Column & c3) const;
  double det(const Column & c1, const Column & c2) const;
   
  double fun(double x) const;

private:
  struct Point { double x; double y; mutable double w; }; 
  mutable std::vector<Point> points;
  bool doErr, hasFixedParC;
  mutable bool hasValues, hasErrors;
  bool hasWeights;
  mutable Result theResult;  
};

#endif