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// $Id: G4LogLogInterpolation.cc,v 1.16 2009/09/25 07:41:34 sincerti Exp $
// GEANT4 tag $Name: geant4-09-04-ref-00 $
//
// Author: Maria Grazia Pia (Maria.Grazia.Pia@cern.ch)
//         Sebastian Incerti (incerti@cenbg.in2p3.fr)
//         Nicolas A. Karakatsanis (knicolas@mail.ntua.gr)
// History:
// -----------
// 31 Jul 2001   MGP        Created
// 27 Jun 2008   SI         Add check to avoid FPE errors
// 08 Dec 2008   NAK        Log-Log interpolation math formula streamlined, self-test function
// 14 Jun 2008   NAK        New implementation for log-log interpolation after directly loading
//                          logarithmic values from G4EMLOW dataset
// -------------------------------------------------------------------

#include "G4LogLogInterpolation.hh"

// Constructor

G4LogLogInterpolation::G4LogLogInterpolation()
{ }

// Destructor

G4LogLogInterpolation::~G4LogLogInterpolation()
{ }

G4VDataSetAlgorithm* G4LogLogInterpolation::Clone() const 
{ return new G4LogLogInterpolation; }


G4double G4LogLogInterpolation::Calculate(G4double x, G4int bin, 
					  const G4DataVector& points, 
					  const G4DataVector& data) const
{
  //G4cout << "G4LogLogInterpolation is performed (2 arguments) " << G4endl;
  G4int nBins = data.size() - 1;
//G4double oldresult = 0.;
  G4double value = 0.;
  if (x < points[0])
    {
      value = 0.;
    }
  else if (bin < nBins)
    {
      G4double e1 = points[bin];
      G4double e2 = points[bin+1];
      G4double d1 = data[bin];
      G4double d2 = data[bin+1];
// Check of e1, e2, d1 and d2 values to avoid floating-point errors when estimating the interpolated value below -- S.I., Jun. 2008
      if ((d1 > 0.) && (d2 > 0.) && (e1 > 0.) && (e2 > 0.))
        {
// Streamline the Log-Log Interpolation formula in order to reduce the required number of log10() function calls
// Variable oldresult contains the result of old implementation of Log-Log interpolation -- M.G.P. Jun. 2001
//       oldresult = (std::log10(d1)*std::log10(e2/x) + std::log10(d2)*std::log10(x/e1)) / std::log10(e2/e1);
//       oldresult = std::pow(10.,oldresult);
// Variable value contains the result of new implementation, after streamlining the math operation -- N.A.K. Oct. 2008
         value = std::log10(d1)+(std::log10(d2/d1)/std::log10(e2/e1)*std::log10(x/e1));
         value = std::pow(10.,value);
// Test of the new implementation result (value variable) against the old one (oldresult) -- N.A.K. Dec. 2008
//       G4double diffResult = value - oldresult;
//       G4double relativeDiff = 1e-11;
// Comparison of the two values based on a max allowable relative difference
//       if ( std::fabs(diffResult) > relativeDiff*std::fabs(oldresult) )
//        {
// Abort comparison when at least one of two results is infinite
//           if ((!std::isinf(oldresult)) && (!std::isinf(value)))
//            {
//              G4cout << "G4LogLogInterpolation> Old Interpolated Value is:" << oldresult << G4endl;
//              G4cout << "G4LogLogInterpolation> New Interpolated Value is:" << value << G4endl << G4endl;
//              G4cerr << "G4LogLogInterpolation> Error in Interpolation:" << G4endl;
//              G4cerr << "The difference between new and old interpolated value is:" << diffResult << G4endl << G4endl;
//            }
//        }
        }
      else value = 0.;
    }
  else
    {
      value = data[nBins];
    }
  return value;
}


// Nicolas A. Karakatsanis: New implementation of log-log interpolation after directly loading 
//                          logarithmic values from G4EMLOW dataset

G4double G4LogLogInterpolation::Calculate(G4double x, G4int bin, 
					  const G4DataVector& points,
                                          const G4DataVector& data,
                                          const G4DataVector& log_points, 
					  const G4DataVector& log_data) const
{
  //G4cout << "G4LogLogInterpolation is performed (4 arguments) " << G4endl;
  G4int nBins = data.size() - 1;
  G4double value = 0.;
  G4double log_x = std::log10(x);
  if (x < points[0])
    {
      value = 0.;
    }
  else if (bin < nBins)
    {
      G4double log_e1 = log_points[bin];
      G4double log_e2 = log_points[bin+1];
      G4double log_d1 = log_data[bin];
      G4double log_d2 = log_data[bin+1];
      
      //G4cout << "x = " << x << " , logx = " << log_x  << " , bin = " << bin << G4endl; 
      //G4cout << "e1 = " << points[bin] << " d1 = " << data[bin] << G4endl;
      //G4cout << "e2 = " << points[bin+1] << " d2 = " << data[bin+1] << G4endl;
      //G4cout << "loge1 = " << log_e1 << " logd1 = " << log_d1 << G4endl;
      //G4cout << "loge2 = " << log_e2 << " logd2 = " << log_d2 << G4endl;

// Values e1, e2, d1 and d2 are the log values of the corresponding
// original energy and data values. Simple linear interpolation performed
// on loagarithmic data should be equivalent to log-log interpolation
      value = log_d1 + (log_d2 - log_d1)*(log_x - log_e1)/(log_e2 - log_e1);

// Delogarithmize to obtain interpolated value
      value = std::pow(10.,value);
   }
 else
   {
     value = data[nBins];
   }
  return value;
}