G4CascadeInterpolator.icc

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#ifndef G4CASCADE_INTERPOLATOR_ICC
#define G4CASCADE_INTERPOLATOR_ICC
// $Id$
//
// 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).
// 20100803  M. Kelsey -- Add printBins() function for debugging
// 20101019  M. Kelsey -- CoVerity reports: recursive #include, index overrun
// 20110728  M. Kelsey -- Fix Coverity #20238, recursive #include.
// 20110923  M. Kelsey -- Add optional ostream& argument to printBins()

#include <iomanip>


// 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<last && 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]));
}


// Print bin edges for debugging

template <int NBINS>
void G4CascadeInterpolator<NBINS>::printBins(std::ostream& os) const {
  os << " G4CascadeInterpolator<" << NBINS << "> : " << G4endl;
  for (G4int k=0; k<NBINS; k++) {
    os << " " << std::setw(5) << xBins[k];
    if ((k+1)%12 == 0) os << G4endl;
  }
  os << G4endl;
}

#endif  /* G4CASCADE_INTERPOLATOR_ICC */

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