ElasticDiffSphere.cpp

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// Mantid Repository : https://github.com/mantidproject/mantid
//
// Copyright © 2018 ISIS Rutherford Appleton Laboratory UKRI,
//   NScD Oak Ridge National Laboratory, European Spallation Source,
//   Institut Laue - Langevin & CSNS, Institute of High Energy Physics, CAS
// SPDX - License - Identifier: GPL - 3.0 +
// Mantid Coding standars <http://www.mantidproject.org/Coding_Standards>
// Main Module Header
#include "MantidCurveFitting/Functions/ElasticDiffSphere.h"
// Mantid Headers from the same project
#include "MantidCurveFitting/Constraints/BoundaryConstraint.h"
// Mantid headers from other projects
#include "MantidAPI/FunctionFactory.h"
#include "MantidAPI/IFunction.h"
 
// third party library headers
#include <boost/math/special_functions/bessel.hpp>
// standard library headers
#include <cmath>
#include <limits>
 
using BConstraint = Mantid::CurveFitting::Constraints::BoundaryConstraint;
 
namespace {
Mantid::Kernel::Logger g_log("ElasticDiffSphere");
}
 
namespace Mantid::CurveFitting::Functions {
 
DECLARE_FUNCTION(ElasticDiffSphere)
 
 
ElasticDiffSphere::ElasticDiffSphere() {
  // parameter "Height" declared in parent DeltaFunction constructor
  // declareParameter("Height", 1.0);
  declareParameter("Radius", 2.0, "Sphere radius");
  FunctionQDepends::declareAttributes();
}
 
void ElasticDiffSphere::init() {
  // Ensure positive values for Height and Radius
  auto HeightConstraint = std::make_unique<BConstraint>(this, "Height", std::numeric_limits<double>::epsilon(), true);
  this->addConstraint(std::move(HeightConstraint));
 
  auto RadiusConstraint = std::make_unique<BConstraint>(this, "Radius", std::numeric_limits<double>::epsilon(), true);
  this->addConstraint(std::move(RadiusConstraint));
}
 
double ElasticDiffSphere::HeightPrefactor() const {
  const double R = this->getParameter("Radius");
  const double Q = this->getAttribute("Q").asDouble();
 
  // Penalize negative parameters
  if (R < std::numeric_limits<double>::epsilon()) {
    return std::numeric_limits<double>::infinity();
  }
 
  return pow(3 * boost::math::sph_bessel(1, Q * R) / (Q * R), 2);
}
 
} // namespace Mantid::CurveFitting::Functions