source: trunk/src/RegressionLinear.h @ 221

// $Id: RegressionLinear.h 221 2004-12-30 22:36:25Z peter $

#ifndef _theplu_statistics_regression_linear_
#define _theplu_statistics_regression_linear_

// C++ tools include
/////////////////////
#include "Regression.h"
#include "vector.h"

// Standard C++ includes
////////////////////////
#include <cmath>

namespace theplu {
namespace statistics {  
  
  ///
  /// Class for Regression.   
  ///
  
  class RegressionLinear : public Regression 
  {
  
  public:
    ///
    /// Default Constructor.
    ///
    RegressionLinear(void);

    ///
    /// Copy Constructor. (not implemented)
    ///
    RegressionLinear(const RegressionLinear&);

    ///
    /// Destructor 
    ///
    virtual ~RegressionLinear(void) {};
         
    ///
    /// @return the parameter \f$ \alpha \f$
    ///
    inline double alpha(void) const { return alpha_; }

    ///
    /// @return standard deviation of parameter \f$ \alpha \f$
    ///
    inline double alpha_var(void) const { return sqrt(alpha_var_); }

    ///
    /// @return the parameter \f$ \beta
    ///
    inline double beta(void) const { return beta_; }

    ///
    /// @return standard devaition of parameter \f$ \beta \f$
    ///
    inline double beta_var(void) const { return sqrt(beta_var_); }
    
    ///
    /// This function computes the best-fit linear regression
    /// coefficients \f$ (\alpha, \beta)\f$ of the model \f$ y =
    /// \alpha + \beta (x-m_x) \f$ from vectors \a x and \a y, by
    /// minimizing \f$ \sum{(y_i - \alpha - \beta (x-m_x))^2} \f$.
    ///
    void fit(const gslapi::vector& x, const gslapi::vector& y) ;
    
    ///
    /// This function computes the best-fit linear regression
    /// coefficients \f$ (\alpha, \beta)\f$ of the model \f$ y =
    /// \alpha + \beta (x-m_x) \f$ from vectors \a x and \a y, by
    /// minimizing \f$ \sum{w_i(y_i - \alpha - \beta (x-m_x))^2} \f$.
    ///
    void fit(const gslapi::vector& x, const gslapi::vector& y,
             const gslapi::vector& w);
    
    ///
    /// Function predicting value using the linear model. \a y_err is
    /// the expected deviation from the line for a new data point. If
    /// weights are used a weight can be specified for the new point.
    ///
    inline void predict(const double x, double& y, double& y_err, 
                        const double w=1.0) const 
    { 
      y = alpha_ + beta_ * (x-m_x_); 
      y_err = sqrt( alpha_var_+beta_var_*(x-m_x_)*(x-m_x_)+s2_/w ); 
    }

    ///
    /// Function returning the coefficient of determination,
    /// i.e. share of variance explained by the linear model.
    ///
    inline double r2(void) const { return r2_; }

  private:
    double alpha_;
    double alpha_var_;
    double beta_;
    double beta_var_;
    double m_x_; // average of x values
    double s2_; // var(y|x)
    double r2_; // coefficient of determination
  };

}} // of namespace statistics and namespace theplu

#endif