Gauss.cpp

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//  ************************************************************************************************
//
//  BornAgain: simulate and fit reflection and scattering
//
//! @file      Sample/SoftParticle/Gauss.cpp
//! @brief     Implements class GaussSphere.
//!
//! @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/SoftParticle/Gauss.h"
#include "Base/Math/Constants.h"
#include "Sample/Shapes/BoxNet.h"
#include <limits>
 
GaussSphere::GaussSphere(const std::vector<double> P)
    : IFormFactor(P)
    , m_mean_radius(m_P[0])
{
    checkNodeArgs();
}
 
GaussSphere::GaussSphere(double mean_radius)
    : GaussSphere(std::vector<double>{mean_radius})
{
}
 
complex_t GaussSphere::formfactor_at_bottom(C3 q) const
{
    const double max_ql = std::sqrt(-4 * M_PI * std::log(std::numeric_limits<double>::min()) / 3);
 
    double qzh = q.z().real() * m_mean_radius;
    if (std::abs(qzh) > max_ql)
        return 0.0;
    double qxr = q.x().real() * m_mean_radius;
    if (std::abs(qxr) > max_ql)
        return 0.0;
    double qyr = q.y().real() * m_mean_radius;
    if (std::abs(qyr) > max_ql)
        return 0.0;
 
    return pow(m_mean_radius, 3) * std::exp(-(qxr * qxr + qyr * qyr + qzh * qzh) / 4.0 / M_PI);
}