fixed_bc.hpp

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// SPDX-FileCopyrightText: 2025 VTT Technical Research Centre of Finland Ltd
// SPDX-License-Identifier: AGPL-3.0-or-later
 
#pragma once
 
#include "openpfc/core/types.hpp"
#include "openpfc/field/operations.hpp"
#include "openpfc/field_modifier.hpp"
 
namespace pfc {
 
using pfc::types::Int3;
 
class FixedBC : public FieldModifier {
 
private:
  double xwidth = 20.0;
  double alpha = 1.0;
  double m_rho_low, m_rho_high;
  std::string m_name = "FixedBC";
 
public:
  FixedBC() = default;
 
  FixedBC(double rho_low, double rho_high)
      : m_rho_low(rho_low), m_rho_high(rho_high) {}
 
  void set_rho_low(double rho_low) { m_rho_low = rho_low; }
  void set_rho_high(double rho_high) { m_rho_high = rho_high; }
 
  const std::string &get_modifier_name() const override { return m_name; }
 
  void apply(Model &m, double) override {
    const World &w = m.get_world();
    const double Lx = get_size(w, 0);
    const double dx = get_spacing(w, 0);
    const double xpos = Lx * dx - xwidth;
 
    pfc::field::apply_inplace(
        m, get_field_name(), [=](const pfc::Real3 &X, double current) {
          const double x = X[0];
          if (std::abs(x - xpos) < xwidth) {
            const double S = 1.0 / (1.0 + std::exp(-alpha * (x - xpos)));
            return m_rho_low * S + m_rho_high * (1.0 - S);
          }
          return current; // outside transition band, keep value
        });
  }
};
 
} // namespace pfc