JPower.hh

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#ifndef __JMATH__JPOWER__
#define __JMATH__JPOWER__
 
#include <istream>
#include <ostream>
#include <cmath>
 
 
/**
 * \author mdejong
 */
 
namespace JMATH {}
namespace JPP { using namespace JMATH; }
 
namespace JMATH {
  
  /**
   * Power law function object.
   *
   * Evaluation of function, derivative and integral values.
   */
  class JPower {
  public:
    /**
     * Constructor.
     *
     * \param  alpha      spectral index
     * \param  factor     multiplication factor
     */
    JPower(const double alpha,
           const double factor = 1.0)
    {
      this->alpha  = alpha;
      this->factor = factor;
    }
 
 
    /**
     * Function value.
     *
     * \param  x          abscissa value
     * \return            function value
     */
    double getValue(const double x) const
    {
      return factor * pow(x, alpha);
    }
 
 
    /**
     * Derivative value.
     *
     * \param  x          abscissa value
     * \return            derivative value
     */
    double getDerivative(const double x) const
    {
      return factor * alpha * pow(x, alpha - 1);
    }
 
 
    /**
     * Integral value.
     *
     * \param  x          abscissa value
     * \return            integral value
     */
    double getIntegral(const double x) const
    {
      if (alpha != -1.0)
        return factor * pow(x, alpha + 1) / (alpha + 1);
      else
        return factor * log(x);
    }
 
 
    /**
     * Function value.
     *
     * \param  x          abscissa value
     * \return            function value
     */
    double operator()(const double x) const
    {
      return getValue(x);
    }
 
 
    /**
     * Read power from input.
     *
     * \param  in         input stream
     * \param  object     power
     * \return            input stream
     */
    friend inline std::istream& operator>>(std::istream& in, JPower& object)
    {
      in >> object.alpha >> object.factor;
      
      return in;
    }
 
 
    /**
     * Write power to output.
     *
     * \param  out        output stream
     * \param  object     trigonometric
     * \return            output stream
     */
    friend inline std::ostream& operator<<(std::ostream& out, const JPower& object)
    {
      return out << object.alpha << ' ' << object.factor;
    }
    
  protected:
    double alpha;
    double factor;
  };
}
 
#endif