interpolation_util.hh

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/// @file   core/interpolation/interpolation_util.hh
/// @brief  Useful function for interpolation...
/// @author Rhiju Das
///

#ifndef INCLUDED_core_scoring_interpolation_util_hh
#define INCLUDED_core_scoring_interpolation_util_hh

#include <core/types.hh>
#include <ObjexxFCL/FArray1D.hh>

namespace core {
namespace scoring {

/////////////////////////////////////////////////////////////////////////////////////////
// A generally useful function for interpolation.
// Its a little puzzling that this isn't in any of the utility::interpolation
// files, but I sure can't find it.
inline
void
interpolate_value_and_deriv(
  ObjexxFCL::FArray1D <Real> const & potential,
  Real const & bin_width,
  Real const & r,
  Real & value,
  Real & deriv )
{

  Size const & NUM_BINS( potential.size() );

  Size r_bin_lo = Size( r/bin_width + 0.5 );
  Size r_bin_hi  = r_bin_lo + 1;

  value = 0.0;
  deriv = 0.0;

  if (r_bin_lo > NUM_BINS ) return;

  if (r_bin_hi > NUM_BINS ){
    value = potential( NUM_BINS );
  } else if (r_bin_lo < 1 ) {
    value = potential( 1 );
  } else {
    Real const fraction = (r/bin_width + 0.5) - r_bin_lo;
    value = ( (1 - fraction ) * potential( r_bin_lo ) +
              fraction * potential( r_bin_hi ) );
    deriv = ( potential( r_bin_hi ) - potential( r_bin_lo ) ) / bin_width;
  }

}

} // end namespace scoring
} // end namespace core

#endif