PlaneWave.hpp

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/*
 * Copyright (C) 2010-2026 The ESPResSo project
 *
 * This file is part of ESPResSo.
 *
 * ESPResSo is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * ESPResSo is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#pragma once
 
#include "jacobian_type.hpp"
 
#include <utils/Vector.hpp>
#include <utils/math/tensor_product.hpp>
 
#include <cmath>
#include <cstddef>
 
namespace FieldCoupling {
namespace Fields {
/**
 * @brief A plane wave.
 *
 * A time-dependent plane wave, with a certain (vector-valued)
 * amplitude, wave vector frequency and phase.
 *
 * See https://en.wikipedia.org/wiki/Plane_wave
 */
template <typename T, std::size_t codim> class PlaneWave {
public:
  using value_type =
      typename Utils::decay_to_scalar<Utils::Vector<T, codim>>::type;
  using jacobian_type = detail::jacobian_type<T, codim>;
 
private:
  value_type m_amplitude;
  value_type m_k;
  T m_omega;
  T m_phase;
 
public:
  PlaneWave(const value_type amplitude, const value_type &k, T omega, T phase)
      : m_amplitude(amplitude), m_k(k), m_omega(omega), m_phase(phase) {}
 
  value_type &amplitude() { return m_amplitude; }
  value_type &k() { return m_k; }
  T &omega() { return m_omega; }
  T &phase() { return m_phase; }
 
  /**
   * @brief Evaluate field.
   *
   * @param x Where?
   * @param t When?
   * @return Value of the field at point x and time t.
   */
  value_type operator()(const Utils::Vector3d &x, T t = 0.) const {
    return m_amplitude * sin(m_k * x - m_omega * t + m_phase);
  }
 
  /**
   * @brief Evaluate the Jacobian matrix of the field.
   *
   * See https://en.wikipedia.org/wiki/Jacobian_matrix_and_determinant
   * In the special case of a scalar field, the Jacobian is the gradient of
   * the field.
   *
   * @param x Where?
   * @param t When?
   * @return Jacobian matrix
   */
  jacobian_type jacobian(const Utils::Vector3d &x, T t = 0.) const {
    return Utils::tensor_product(m_amplitude, m_k) *
           cos(m_k * x - m_omega * t + m_phase);
  }
 
  bool fits_in_box(const Utils::Vector3d &) const { return true; }
};
} // namespace Fields
} // namespace FieldCoupling