HollowSphere.cpp

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//  ************************************************************************************************
//
//  BornAgain: simulate and fit reflection and scattering
//
//! @file      Sample/HardParticle/HollowSphere.cpp
//! @brief     Implements class HollowSphere.
//!
//! @homepage  http://www.bornagainproject.org
//! @license   GNU General Public License v3 or higher (see COPYING)
//! @copyright Forschungszentrum Jülich GmbH 2018
//! @authors   Scientific Computing Group at MLZ (see CITATION, AUTHORS)
//
//  ************************************************************************************************
 
#include "Sample/HardParticle/HollowSphere.h"
#include "Base/Math/Constants.h"
#include "Sample/Shapes/TruncatedEllipsoidNet.h"
#include <limits>
 
HollowSphere::HollowSphere(const std::vector<double> P)
    : IFormFactor(P)
    , m_mean(m_P[0])
    , m_full_width(m_P[1])
{
    checkNodeArgs();
    if (!checkParameters())
        throw std::runtime_error("HollowSphere::HollowSphere:"
                                 " mean radius must be bigger than the half width");
    m_shape3D = std::make_unique<TruncatedEllipsoidNet>(m_mean, m_mean, m_mean, 2.0 * m_mean, 0.0);
}
 
HollowSphere::HollowSphere(double mean, double full_width)
    : HollowSphere(std::vector<double>{mean, full_width})
{
}
 
complex_t HollowSphere::formfactor_at_bottom(C3 q) const
{
    double R = m_mean;
    double W = m_full_width;
    double q2 = std::norm(q.x()) + std::norm(q.y()) + std::norm(q.z());
    double q_r = std::sqrt(q2);
    if (q_r * R < std::numeric_limits<double>::epsilon())
        return (4.0 * M_PI * R * R * R + M_PI * R * W * W) / 3.0;
    double qR = q_r * R;
    double qW = q_r * W;
    double nominator =
        4 * M_PI
        * (4 * std::sin(qR) * std::sin(qW / 2.0) - qW * std::cos(qW / 2.0) * std::sin(qR)
           - 2.0 * qR * std::cos(qR) * std::sin(qW / 2.0));
    return nominator / (q2 * q2 * W);
}
 
bool HollowSphere::checkParameters() const
{
    if (m_full_width <= 0.0)
        return false;
    if (2.0 * m_mean < m_full_width)
        return false;
    return true;
}