gravity_derivatives.h

/*******************************************************************************
 * This file is part of SWIFT.
 * Copyright (c) 2016 Matthieu Schaller (matthieu.schaller@durham.ac.uk)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 ******************************************************************************/
#ifndef SWIFT_GRAVITY_DERIVATIVE_H
#define SWIFT_GRAVITY_DERIVATIVE_H

/* Some standard headers. */
#include <math.h>

/* Local headers. */
#include "inline.h"

/**
 * @brief \f$ \phi(r_x, r_y, r_z) \f$.
 */
__attribute__((always_inline)) INLINE static double D_000(double r_x,
                                                          double r_y,
                                                          double r_z,
                                                          double r_inv) {

  return r_inv;
}

/**
 * @brief \f$ \frac{\partial\phi(r_x, r_y, r_z)}{\partial r_x} \f$.
 */
__attribute__((always_inline)) INLINE static double D_100(double r_x,
                                                          double r_y,
                                                          double r_z,
                                                          double r_inv) {

  return -r_x * r_inv * r_inv * r_inv;
}

/**
 * @brief \f$ \frac{\partial\phi(r_x, r_y, r_z)}{\partial r_x} \f$.
 */
__attribute__((always_inline)) INLINE static double D_010(double r_x,
                                                          double r_y,
                                                          double r_z,
                                                          double r_inv) {

  return -r_y * r_inv * r_inv * r_inv;
}

/**
 * @brief \f$ \frac{\partial\phi(r_x, r_y, r_z)}{\partial r_x} \f$.
 */
__attribute__((always_inline)) INLINE static double D_001(double r_x,
                                                          double r_y,
                                                          double r_z,
                                                          double r_inv) {

  return -r_z * r_inv * r_inv * r_inv;
}

#endif /* SWIFT_GRAVITY_DERIVATIVE_H */