source: trunk/source/processes/hadronic/models/cascade/cascade/include/G4CascadeInterpolator.icc @ 1316

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// $Id: G4CascadeInterpolator.icc,v 1.5 2010/06/08 06:29:34 stesting Exp $
// GEANT4 tag $Name: geant4-09-04-beta-cand-01 $
//
// Author:  Michael Kelsey <kelsey@slac.stanford.edu>
//
// Simple linear interpolation class, more lightweight than
// G4PhysicsVector.  Templated on number of X-axis (usually energy)
// bins, constructor takes a C-array of bin edges as input, and an
// optional flag whether to truncate or extrapolate (the default) values
// beyond the bin boundaries.
//
// The interpolation action returns a simple double: the integer part
// is the bin index, and the fractional part is, obviously, the
// fractional part.
//
// 20100517  M. Kelsey -- Bug fix in interpolate:  If bin position is _exactly_
//              at upper edge (== last + 0.0), just return bin value.
// 20100520  M. Kelsey -- Second bug fix:  Loop in bin search should start at
//              i=1, not i=0 (since i-1 is the key).

#include "G4CascadeInterpolator.hh"


// Find bin position (index and fraction) using input argument and array

template <int NBINS>
G4double G4CascadeInterpolator<NBINS>::getBin(const G4double x) const {
  if (x == lastX) return lastVal;       // Avoid unnecessary work

  G4double xindex, xdiff, xbin;

  lastX = x;
  if (x < xBins[0]) {                   // Handle boundaries first
    xindex = 0.;
    xbin = xBins[1]-xBins[0];
    xdiff = doExtrapolation ? x-xBins[0] : 0.;          // Less than zero
  } else if (x >= xBins[last]) {
    xindex = last;
    xbin = xBins[last]-xBins[last-1];
    xdiff = doExtrapolation ? x-xBins[last] : 0.;
  } else {                              // Assume nBins small; linear search
    int i;
    for (i=1; i<nBins && x>xBins[i]; i++) {;}   // Stops when x within bin i-1
    xindex = i-1;
    xbin = xBins[i] - xBins[i-1];
    xdiff = x - xBins[i-1];
  }

#ifdef G4CASCADE_DEBUG_SAMPLER
  G4cout << " G4CascadeInterpolator<" << NBINS << ">: x=" << x
         << " index=" << xindex << " fraction=" << xdiff/xbin << G4endl;
#endif

  return (lastVal = xindex + xdiff/xbin);       // Save return value for later
}


// Apply interpolation of input argument to user array

template <int NBINS>
G4double G4CascadeInterpolator<NBINS>::
interpolate(const G4double x, const G4double (&yb)[nBins]) const {
  getBin(x);
  return interpolate(yb);
}

// Apply last found interpolation to user array

template <int NBINS>
G4double G4CascadeInterpolator<NBINS>::
interpolate(const G4double (&yb)[nBins]) const {
  // Treat boundary extrapolations specially, otherwise just truncate
  G4int i = (lastVal<0) ? 0 : (lastVal>last) ? last-1 : G4int(lastVal);
  G4double frac = lastVal - G4double(i);        // May be <0 or >1 if extrapolating

  // Special case:  if exactly on upper bin edge, just return value
  return (i==last) ? yb[last] : (yb[i] + frac*(yb[i+1]-yb[i]));
}