MagneticFormFactorTable.cpp

// Includes
#include "MantidKernel/MagneticFormFactorTable.h"

namespace Mantid
{
  namespace PhysicalConstants
  {

    /**
     * Constructs the table for the given ion, J & L
     * @param length :: scattering length
     * @param ion :: A reference to the required ion
     * @param j :: The total angular momentum
     * @param l :: The orbital angular momentum
     */
    MagneticFormFactorTable::MagneticFormFactorTable(const size_t length, const MagneticIon & ion,
                                                     const uint16_t j, const uint16_t l)
      : m_length(length), m_lookup(length, 0.0), m_delta(0.0)
    {
      setup(ion, j, l);
    }

    /**
     * Returns an interpolated form factor for the given \f$Q^2\f$ value
     * @param qsqr :: \f$Q^2\f$ in \f$\mbox{\AA}^{-2}\f$
     * @return The interpolated value
     */
    double MagneticFormFactorTable::value(const double qsqr) const
    {
      const double nintervals = qsqr/m_delta;
      const size_t index = static_cast<size_t>(nintervals);
      if(index < m_length)
      {
        const double fraction = nintervals - static_cast<double>(index);
        return (1.0 - fraction)*m_lookup[index] + fraction*m_lookup[index+1];
      }
      else return 0.0;
    }

    //-------------------------------------------------------------------------------------------------------
    // Private methods
    //-------------------------------------------------------------------------------------------------------

    /**
     * Setup the table with the values for the given ion, J & L.
     * @param ion :: A reference to the required ion
     * @param j :: The total angular momentum
     * @param l :: The orbital angular momentum
     */
    void MagneticFormFactorTable::setup(const MagneticIon & ion, const uint16_t j, const uint16_t l)
    {
      const size_t length = m_length;
      const double qsqrMax = MagneticIon::formFactorCutOff(j,l);
      m_delta = qsqrMax/static_cast<double>(length);

      for(size_t i = 0; i < length; ++i)
      {
        const double qsqr = m_delta*static_cast<double>(i);
        m_lookup[i] = ion.analyticalFormFactor(qsqr, j, l);
      }
    }


  } // namespace Kernel
} // namespace Mantid