PhysicsTools/MVAComputer/interface/Spline.h - master - githubmirror/cmssw

PhysicsTools/MVAComputer/interface/Spline.h
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#ifndef PhysicsTools_MVAComputer_Spline_h
#define PhysicsTools_MVAComputer_Spline_h
// -*- C++ -*-
//
// Package:     MVAComputer
// Class  :     Spline
//

//
// Author:	Christophe Saout <christophe.saout@cern.ch>
// Created:     Sat Apr 24 15:18 CEST 2007
//

namespace PhysicsTools {

  /** \class Spline
 *
 * \short A simple class for cubic splines
 *
 * This class implements cubic splines for n equidistant points in x
 * between 0 and 1. It is constructed from an array of n y coordinates
 * and can compute the interpolated y coordinate for a given x.
 *
 ************************************************************/
  class Spline {
  public:
    Spline();
    Spline(const Spline &orig);

    /// construct spline from \a n y coordinates in array \a vals
    Spline(unsigned int n, const double *vals);
    ~Spline();

    Spline &operator=(const Spline &orig);

    /// initialize spline from \a n y coordinates in array \a vals
    void set(unsigned int n, const double *vals);

    /// compute y coordinate at x coordinate \a x
    float eval(float x) const;

    /// compute the derivate at x coordinate \a x
    float deriv(float x) const;

    /// compute integral under curve between 0 and \a x
    float integral(float x) const;

    /// total area (integral between 0 and 1) under curve
    float getArea() const { return area; }

    /// return the number of entries
    inline unsigned int numberOfEntries() const { return n + 1; }

  private:
    /// internal class describing a "segment" (between two x points)
    struct Segment {
      float coeffs[4];
      float area;

      float eval(float x) const;
      float deriv(float x) const;
      float integral(float x) const;
    };

    unsigned int n;
    Segment *segments;
    float area;
  };

}  // namespace PhysicsTools

#endif  // PhysicsTools_MVAComputer_Spline_h