TSpline1.cxx

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// @(#)root/tmva $Id$
// Author: Andreas Hoecker, Joerg Stelzer, Helge Voss
 
/**********************************************************************************
 * Project: TMVA - a Root-integrated toolkit for multivariate data analysis       *
 * Package: TMVA                                                                  *
 * Class  : TSpline1                                                              *
 *                                             *
 *                                                                                *
 * Description:                                                                   *
 *      Implementation (see header for description)                               *
 *                                                                                *
 * Authors (alphabetical):                                                        *
 *      Andreas Hoecker <Andreas.Hocker@cern.ch> - CERN, Switzerland              *
 *      Helge Voss      <Helge.Voss@cern.ch>     - MPI-K Heidelberg, Germany      *
 *      Kai Voss        <Kai.Voss@cern.ch>       - U. of Victoria, Canada         *
 *                                                                                *
 * Copyright (c) 2005:                                                            *
 *      CERN, Switzerland                                                         *
 *      U. of Victoria, Canada                                                    *
 *      MPI-K Heidelberg, Germany                                                 *
 *                                                                                *
 * Redistribution and use in source and binary forms, with or without             *
 * modification, are permitted according to the terms listed in LICENSE           *
 * (see tmva/doc/LICENSE)                                          *
 **********************************************************************************/
 
/*! \class TMVA::TSpline1
\ingroup TMVA
Linear interpolation of TGraph
*/
 
#include "TMVA/TSpline1.h"
 
#include "TGraph.h"
#include "TMath.h"
 
 
////////////////////////////////////////////////////////////////////////////////
/// constructor from TGraph pointer (not owned by TSpline1)
/// TSpline is a TNamed object
 
TMVA::TSpline1::TSpline1( const TString& title, const TGraph *theGraph )
: fX(theGraph->GetX(), theGraph->GetX() + theGraph->GetN()),
  fY(theGraph->GetY(), theGraph->GetY() + theGraph->GetN())
{
   SetNameTitle( title, title );
}
 
////////////////////////////////////////////////////////////////////////////////
/// destructor
 
TMVA::TSpline1::~TSpline1( void ) {}
 
////////////////////////////////////////////////////////////////////////////////
/// returns linearly interpolated TGraph entry around x
 
Double_t TMVA::TSpline1::Eval( Double_t x ) const
{
   Int_t N = fX.size();
   Int_t ibin = std::distance(std::lower_bound(fX.rbegin(), fX.rend(), x, std::greater{}), fX.rend()) - 1;
   // sanity checks
   if (ibin < 0 ) ibin = 0;
   if (ibin >= N) ibin = N - 1;
 
   Int_t nextbin = ibin;
   if ((x > fX[ibin] && ibin != N-1) || ibin == 0)
      nextbin++;
   else
      nextbin--;
 
   // linear interpolation
   Double_t dx = fX[ibin] - fX[nextbin];
   Double_t dy = fY[ibin] - fY[nextbin];
   return fY[ibin] + (x - fX[ibin]) * dy/dx;
}
 
////////////////////////////////////////////////////////////////////////////////
/// no coefficients to precompute
 
void TMVA::TSpline1::BuildCoeff( void )
{
}
 
////////////////////////////////////////////////////////////////////////////////
/// no knots
 
void TMVA::TSpline1::GetKnot( Int_t /* i*/, Double_t&  /*x*/, Double_t& /*y*/ ) const
{
}