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Matthieu Schaller authoredMatthieu Schaller authored
gravity.c 6.54 KiB
/*******************************************************************************
* This file is part of SWIFT.
* Copyright (c) 2017 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/>.
*
******************************************************************************/
/* Config parameters. */
#include "../config.h"
/* Some standard headers. */
#include <stdio.h>
/* This object's header. */
#include "gravity.h"
/* Local headers. */
#include "active.h"
#include "error.h"
/**
* @brief Run a brute-force gravity calculation for a subset of particles.
*
* All gpart with ID modulo SWIFT_GRAVITY_FORCE_CHECKS will get their forces
* computed.
*
* @param s The #space to use.
* @param e The #engine (to access the current time).
*/
void gravity_exact_force_compute(struct space *s, const struct engine *e) {
#ifdef SWIFT_GRAVITY_FORCE_CHECKS
const ticks tic = getticks();
const double const_G = e->physical_constants->const_newton_G;
int counter = 0;
for (size_t i = 0; i < s->nr_gparts; ++i) {
struct gpart *gpi = &s->gparts[i];
/* Is the particle active and part of the subset to be tested ? */
if (gpi->id_or_neg_offset % SWIFT_GRAVITY_FORCE_CHECKS == 0 &&
gpart_is_active(gpi, e)) {
/* Be ready for the calculation */
gpi->a_grav[0] = 0.f;
gpi->a_grav[1] = 0.f;
gpi->a_grav[2] = 0.f;
/* Interact it with all other particles in the space.*/
for (size_t j = 0; j < s->nr_gparts; ++j) {
/* No self interaction */
if (i == j) continue;
struct gpart *gpj = &s->gparts[j];
/* Compute the pairwise distance. */
float dx[3] = {gpi->x[0] - gpj->x[0], // x
gpi->x[1] - gpj->x[1], // y
gpi->x[2] - gpj->x[2]}; // z
const float r2 = dx[0] * dx[0] + dx[1] * dx[1] + dx[2] * dx[2];
runner_iact_grav_pp_nonsym(0.f, r2, dx, gpi, gpj);
}
/* Finish the calculation */
gravity_end_force(gpi, const_G);
/* Store the exact answer */
gpi->a_grav_exact[0] = gpi->a_grav[0];
gpi->a_grav_exact[1] = gpi->a_grav[1];
gpi->a_grav_exact[2] = gpi->a_grav[2];
/* Restore everything */
gpi->a_grav[0] = 0.f;
gpi->a_grav[1] = 0.f;
gpi->a_grav[2] = 0.f;
counter++;
}
}
message("Computed exact gravity for %d gparts (took %.3f %s). ", counter,
clocks_from_ticks(getticks() - tic), clocks_getunit());
#else
error("Gravity checking function called without the corresponding flag.");
#endif
}
/**
* @brief Check the accuracy of the gravity calculation by comparing the
* accelerations
* to the brute-force computed ones.
*
* All gpart with ID modulo SWIFT_GRAVITY_FORCE_CHECKS will be checked.
*
* @param s The #space to use.
* @param e The #engine (to access the current time).
* @param rel_tol The maximal relative error. Will call error() if one particle
* has a larger error.
*/
void gravity_exact_force_check(struct space *s, const struct engine *e,
float rel_tol) {
#ifdef SWIFT_GRAVITY_FORCE_CHECKS
// const double const_G = e->physical_constants->const_newton_G;
int counter = 0;
/* Some accumulators */
float err_rel_max = 0.f;
float err_rel_min = FLT_MAX;
float err_rel_mean = 0.f;
float err_rel_mean2 = 0.f;
float err_rel_std = 0.f;
char file_name[100];
sprintf(file_name, "gravity_checks_step%d_order%d.dat", e->step,
SELF_GRAVITY_MULTIPOLE_ORDER);
FILE *file = fopen(file_name, "w");
fprintf(
file,
"# id a_exact[0] a_exact[1] a_exact[2] a_grav[0] a_grav[1] a_grav[2]\n");
for (size_t i = 0; i < s->nr_gparts; ++i) {
struct gpart *gpi = &s->gparts[i];
/* Is the particle was active and part of the subset to be tested ? */
if (gpi->id_or_neg_offset % SWIFT_GRAVITY_FORCE_CHECKS == 0 &&
gpart_is_starting(gpi, e)) {
fprintf(file, "%16lld %12.5e %12.5e %12.5e %12.5e %12.5e %12.5e \n",
gpi->id_or_neg_offset, gpi->a_grav_exact[0], gpi->a_grav_exact[1],
gpi->a_grav_exact[2], gpi->a_grav[0], gpi->a_grav[1],
gpi->a_grav[2]);
const float diff[3] = {gpi->a_grav[0] - gpi->a_grav_exact[0],
gpi->a_grav[1] - gpi->a_grav_exact[1],
gpi->a_grav[2] - gpi->a_grav_exact[2]};
const float diff_norm =
sqrtf(diff[0] * diff[0] + diff[1] * diff[1] + diff[2] * diff[2]);
const float a_norm = sqrtf(gpi->a_grav_exact[0] * gpi->a_grav_exact[0] +
gpi->a_grav_exact[1] * gpi->a_grav_exact[1] +
gpi->a_grav_exact[2] * gpi->a_grav_exact[2]);
/* Compute relative error */
const float err_rel = diff_norm / a_norm;
/* Check that we are not above tolerance */
if (err_rel > rel_tol) {
message(
"Error too large ! gp->a_grav=[%3.6e %3.6e %3.6e] "
"gp->a_exact=[%3.6e %3.6e %3.6e], "
"gp->num_interacted=%lld, err=%f",
gpi->a_grav[0], gpi->a_grav[1], gpi->a_grav[2],
gpi->a_grav_exact[0], gpi->a_grav_exact[1], gpi->a_grav_exact[2],
gpi->num_interacted, err_rel);
continue;
}
/* Construct some statistics */
err_rel_max = max(err_rel_max, fabsf(err_rel));
err_rel_min = min(err_rel_min, fabsf(err_rel));
err_rel_mean += err_rel;
err_rel_mean2 += err_rel * err_rel;
counter++;
}
}
/* Be nice */
fclose(file);
/* Final operation on the stats */
if (counter > 0) {
err_rel_mean /= counter;
err_rel_mean2 /= counter;
err_rel_std = sqrtf(err_rel_mean2 - err_rel_mean * err_rel_mean);
}
/* Report on the findings */
message("Checked gravity for %d gparts.", counter);
message("Error on |a_grav|: min=%e max=%e mean=%e std=%e", err_rel_min,
err_rel_max, err_rel_mean, err_rel_std);
#else
error("Gravity checking function called without the corresponding flag.");
#endif
}