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Matthieu Schaller authoredMatthieu Schaller authored
kernel_gravity.h 3.49 KiB
/*******************************************************************************
* This file is part of SWIFT.
* Copyright (c) 2012 Pedro Gonnet (pedro.gonnet@durham.ac.uk)
* 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_KERNEL_GRAVITY_H
#define SWIFT_KERNEL_GRAVITY_H
#include <math.h>
/* Includes. */
#include "const.h"
#include "inline.h"
#include "vector.h"
/* The gravity kernel is defined as a degree 6 polynomial in the distance
r. The resulting value should be post-multiplied with r^-3, resulting
in a polynomial with terms ranging from r^-3 to r^3, which are
sufficient to model both the direct potential as well as the splines
near the origin.
As in the hydro case, the 1/h^3 needs to be multiplied in afterwards */
/* Coefficients for the kernel. */
#define kernel_grav_name "Gadget-2 softening kernel"
#define kernel_grav_degree 6 /* Degree of the polynomial */
#define kernel_grav_ivals 2 /* Number of branches */
static const float
kernel_grav_coeffs[(kernel_grav_degree + 1) * (kernel_grav_ivals + 1)]
__attribute__((aligned(16))) = {32.f,
-38.4f,
0.f,
10.66666667f,
0.f,
0.f,
0.f, /* 0 < u < 0.5 */
-10.66666667f,
38.4f,
-48.f,
21.3333333f,
0.f,
0.f,
-0.066666667f, /* 0.5 < u < 1 */
0.f,
0.f,
0.f,
0.f,
0.f,
0.f,
0.f}; /* 1 < u */
/**
* @brief Computes the gravity softening function.
*
* @param u The ratio of the distance to the softening length $u = x/h$.
* @param W (return) The value of the kernel function $W(x,h)$.
*/
__attribute__((always_inline)) INLINE static void kernel_grav_eval(
float u, float *const W) {
/* Pick the correct branch of the kernel */
const int ind = (int)fminf(u * (float)kernel_grav_ivals, kernel_grav_ivals);
const float *const coeffs =
&kernel_grav_coeffs[ind * (kernel_grav_degree + 1)];
/* First two terms of the polynomial ... */
float w = coeffs[0] * u + coeffs[1];
/* ... and the rest of them */
for (int k = 2; k <= kernel_grav_degree; k++) w = u * w + coeffs[k];
/* Return everything */
*W = w / (u * u * u);
}
#endif // SWIFT_KERNEL_GRAVITY_H