Merge branch 'master' into AVX512-Fixes

Conflicts:
	tests/testPair.c

examples/EAGLE_12/eagle_12.yml

@@ -26,7 +26,7 @@ Statistics:
 # Parameters for the self-gravity scheme
 Gravity:
   eta:                   0.025    # Constant dimensionless multiplier for time integration.
-  epsilon:               0.0001   # Softening length (in internal units).
+  epsilon:               0.001    # Softening length (in internal units).
   theta:                 0.7      # Opening angle (Multipole acceptance criterion)
   
 # Parameters for the hydrodynamics scheme

examples/EAGLE_6/eagle_6.yml

@@ -12,6 +12,9 @@ TimeIntegration:
   time_end:   1e-2  # The end time of the simulation (in internal units).
   dt_min:     1e-10 # The minimal time-step size of the simulation (in internal units).
   dt_max:     1e-4  # The maximal time-step size of the simulation (in internal units).
+
+Scheduler:
+  cell_split_size: 64
   
 # Parameters governing the snapshots
 Snapshots:

examples/PerturbedBox_2D/perturbedPlane.yml

@@ -9,7 +9,7 @@ InternalUnitSystem:
 # Parameters governing the time integration
 TimeIntegration:
   time_begin: 0.    # The starting time of the simulation (in internal units).
-  time_end:   10.   # The end time of the simulation (in internal units).
+  time_end:   1000. # The end time of the simulation (in internal units).
   dt_min:     1e-6  # The minimal time-step size of the simulation (in internal units).
   dt_max:     1e-2  # The maximal time-step size of the simulation (in internal units).
 
@@ -21,12 +21,11 @@ Snapshots:
 
 # Parameters governing the conserved quantities statistics
 Statistics:
-  delta_time:          1e-3 # Time between statistics output
+  delta_time:          1.   # Time between statistics output
 
 # Parameters for the hydrodynamics scheme
 SPH:
   resolution_eta:        1.2348   # Target smoothing length in units of the mean inter-particle separation (1.2348 == 48Ngbs with the cubic spline kernel).
-  delta_neighbours:      0.1      # The tolerance for the targetted number of neighbours.
   CFL_condition:         0.1      # Courant-Friedrich-Levy condition for time integration.
   
 # Parameters related to the initial conditions

examples/PerturbedBox_3D/perturbedBox.yml

@@ -9,9 +9,9 @@ InternalUnitSystem:
 # Parameters governing the time integration
 TimeIntegration:
   time_begin: 0.    # The starting time of the simulation (in internal units).
-  time_end:   1.    # The end time of the simulation (in internal units).
+  time_end:   1000  # The end time of the simulation (in internal units).
   dt_min:     1e-6  # The minimal time-step size of the simulation (in internal units).
-  dt_max:     1e-3  # The maximal time-step size of the simulation (in internal units).
+  dt_max:     1e-2  # The maximal time-step size of the simulation (in internal units).
 
 # Parameters governing the snapshots
 Snapshots:
@@ -21,12 +21,11 @@ Snapshots:
 
 # Parameters governing the conserved quantities statistics
 Statistics:
-  delta_time:          1e-3 # Time between statistics output
+  delta_time:          1. # Time between statistics output
 
 # Parameters for the hydrodynamics scheme
 SPH:
   resolution_eta:        1.2348   # Target smoothing length in units of the mean inter-particle separation (1.2348 == 48Ngbs with the cubic spline kernel).
-  delta_neighbours:      0.1      # The tolerance for the targetted number of neighbours.
   CFL_condition:         0.1      # Courant-Friedrich-Levy condition for time integration.
   
 # Parameters related to the initial conditions

examples/main.c

@@ -190,7 +190,11 @@ int main(int argc, char *argv[]) {
   while ((c = getopt(argc, argv, "acCdDef:FgGhMn:P:sSt:Tv:y:Y:")) != -1)
     switch (c) {
       case 'a':
+#if defined(HAVE_SETAFFINITY) && defined(HAVE_LIBNUMA)
         with_aff = 1;
+#else
+        error("Need NUMA support for thread affinity");
+#endif
         break;
       case 'c':
         with_cosmology = 1;
@@ -392,8 +396,12 @@ int main(int argc, char *argv[]) {
     parser_read_file(paramFileName, params);
 
     /* Handle any command-line overrides. */
-    if (nparams > 0)
+    if (nparams > 0) {
+      message(
+          "Overwriting values read from the YAML file with command-line "
+          "values.");
       for (int k = 0; k < nparams; k++) parser_set_param(params, cmdparams[k]);
+    }
 
     /* And dump the parameters as used. */
     // parser_print_params(&params);
@@ -565,6 +573,11 @@ int main(int argc, char *argv[]) {
     message("nr of cells at depth %i is %i.", data[0], data[1]);
   }
 
+/* Initialise the table of Ewald corrections for the gravity checks */
+#ifdef SWIFT_GRAVITY_FORCE_CHECKS
+  if (periodic) gravity_exact_force_ewald_init(dim[0]);
+#endif
+
   /* Initialise the external potential properties */
   struct external_potential potential;
   if (with_external_gravity)

src/Makefile.am

@@ -64,7 +64,7 @@ nobase_noinst_HEADERS = align.h approx_math.h atomic.h cycle.h error.h inline.h
 		 kernel_long_gravity.h vector.h cache.h runner_doiact.h runner_doiact_vec.h runner_doiact_grav.h runner_doiact_fft.h \
                  runner_doiact_nosort.h units.h intrinsics.h minmax.h kick.h timestep.h drift.h adiabatic_index.h io_properties.h \
 		 dimension.h equation_of_state.h part_type.h periodic.h \
-		 gravity.h gravity_io.h \
+		 gravity.h gravity_io.h gravity_cache.h \
 		 gravity/Default/gravity.h gravity/Default/gravity_iact.h gravity/Default/gravity_io.h \
 		 gravity/Default/gravity_debug.h gravity/Default/gravity_part.h  \
 		 sourceterms.h \

src/align.h

@@ -23,9 +23,55 @@
  * @brief The default struct alignment in SWIFT.
  */
 #define SWIFT_STRUCT_ALIGNMENT 32
+
 /**
  * @brief Defines alignment of structures
  */
 #define SWIFT_STRUCT_ALIGN __attribute__((aligned(SWIFT_STRUCT_ALIGNMENT)))
 
+/**
+ * @brief The default cache alignment in SWIFT.
+ */
+#define SWIFT_CACHE_ALIGNMENT 64
+
+/**
+ * @brief Defines alignment of caches
+ */
+#define SWIFT_CACHE_ALIGN __attribute__((aligned(SWIFT_CACHE_ALIGNMENT)))
+
+/**
+ * @brief Macro to tell the compiler that a given array has the specified
+ * alignment.
+ *
+ * Note that this turns into a no-op but gives information to the compiler.
+ *
+ * @param array The array.
+ * @param alignment The alignment in bytes of the array.
+ */
+#if defined(__ICC)
+#define swift_align_information(array, alignment) \
+  __assume_aligned(array, alignment);
+#elif defined(__GNUC__)
+#define swift_align_information(array, alignment) \
+  array = __builtin_assume_aligned(array, alignment);
+#else
+#define swift_align_information(array, alignment) ;
+#endif
+
+/**
+ * @brief Macro to tell the compiler that a given number is 0 modulo a given
+ * size.
+ *
+ * Note that this turns into a no-op but gives information to the compiler.
+ * GCC does not have the equivalent built-in so defaults to nothing.
+ *
+ * @param var The variable
+ * @param size The modulo of interest.
+ */
+#if defined(__ICC)
+#define swift_assume_size(var, size) __assume(var % size == 0);
+#else
+#define swift_assume_size(var, size) ;
+#endif
+
 #endif /* SWIFT_ALIGN_H */

src/debug.c

@@ -26,6 +26,7 @@
 /* Some standard headers. */
 #include <float.h>
 #include <stdio.h>
+#include <unistd.h>
 
 /* This object's header. */
 #include "debug.h"
@@ -450,3 +451,69 @@ void dumpCellRanks(const char *prefix, struct cell *cells_top, int nr_cells) {
 }
 
 #endif /* HAVE_MPI */
+
+/**
+ * @brief parse the process /proc/self/statm file to get the process
+ *        memory use (in KB). Top field in ().
+ *
+ * @param size     total virtual memory (VIRT)
+ * @param resident resident non-swapped memory (RES)
+ * @param share    shared (mmap'd) memory  (SHR)
+ * @param trs      text (exe) resident set (CODE)
+ * @param lrs      library resident set
+ * @param drs      data+stack resident set (DATA)
+ * @param dt       dirty pages (nDRT)
+ */
+void getProcMemUse(long *size, long *resident, long *share, long *trs,
+                   long *lrs, long *drs, long *dt) {
+
+  /* Open the file. */
+  FILE *file = fopen("/proc/self/statm", "r");
+  if (file != NULL) {
+    int nscan = fscanf(file, "%ld %ld %ld %ld %ld %ld %ld", size, resident,
+                       share, trs, lrs, drs, dt);
+
+    if (nscan == 7) {
+      /* Convert pages into bytes. Usually 4096, but could be 512 on some
+       * systems so take care in conversion to KB. */
+      long sz = sysconf(_SC_PAGESIZE);
+      *size *= sz;
+      *resident *= sz;
+      *share *= sz;
+      *trs *= sz;
+      *lrs *= sz;
+      *drs *= sz;
+      *dt *= sz;
+
+      *size /= 1024;
+      *resident /= 1024;
+      *share /= 1024;
+      *trs /= 1024;
+      *lrs /= 1024;
+      *drs /= 1024;
+      *dt /= 1024;
+    } else {
+      error("Failed to read sufficient fields from /proc/self/statm");
+    }
+    fclose(file);
+  } else {
+    error("Failed to open /proc/self/statm");
+  }
+}
+
+/**
+ * @brief Print the current memory use of the process. A la "top".
+ */
+void printProcMemUse() {
+  long size;
+  long resident;
+  long share;
+  long trs;
+  long lrs;
+  long drs;
+  long dt;
+  getProcMemUse(&size, &resident, &share, &trs, &lrs, &drs, &dt);
+  printf("## VIRT = %ld , RES = %ld , SHR = %ld , CODE = %ld, DATA = %ld\n",
+         size, resident, share, trs, drs);
+  fflush(stdout);
+}

src/debug.h

@@ -44,4 +44,7 @@ void dumpMETISGraph(const char *prefix, idx_t nvtxs, idx_t ncon, idx_t *xadj,
 void dumpCellRanks(const char *prefix, struct cell *cells_top, int nr_cells);
 #endif
 
+void getProcMemUse(long *size, long *resident, long *share, long *trs,
+                   long *lrs, long *drs, long *dt);
+void printProcMemUse();
 #endif /* SWIFT_DEBUG_H */

src/engine.c

@@ -57,6 +57,7 @@
 #include "error.h"
 #include "gravity.h"
 #include "hydro.h"
+#include "map.h"
 #include "minmax.h"
 #include "parallel_io.h"
 #include "part.h"
@@ -153,7 +154,7 @@ void engine_make_hierarchical_tasks(struct engine *e, struct cell *c) {
 
   struct scheduler *s = &e->sched;
   const int periodic = e->s->periodic;
-  const int is_hydro = (e->policy & engine_policy_hydro);
+  const int is_with_hydro = (e->policy & engine_policy_hydro);
   const int is_self_gravity = (e->policy & engine_policy_self_gravity);
   const int is_with_cooling = (e->policy & engine_policy_cooling);
   const int is_with_sourceterms = (e->policy & engine_policy_sourceterms);
@@ -162,15 +163,19 @@ void engine_make_hierarchical_tasks(struct engine *e, struct cell *c) {
   if (c->super == c) {
 
     /* Add the sort task. */
-    c->sorts =
-        scheduler_addtask(s, task_type_sort, task_subtype_none, 0, 0, c, NULL);
+    if (is_with_hydro) {
+      c->sorts = scheduler_addtask(s, task_type_sort, task_subtype_none, 0, 0,
+                                   c, NULL);
+    }
 
     /* Local tasks only... */
     if (c->nodeID == e->nodeID) {
 
       /* Add the drift task. */
-      c->drift_part = scheduler_addtask(s, task_type_drift_part,
-                                        task_subtype_none, 0, 0, c, NULL);
+      if (is_with_hydro) {
+        c->drift_part = scheduler_addtask(s, task_type_drift_part,
+                                          task_subtype_none, 0, 0, c, NULL);
+      }
 
       /* Add the two half kicks */
       c->kick1 = scheduler_addtask(s, task_type_kick1, task_subtype_none, 0, 0,
@@ -207,7 +212,7 @@ void engine_make_hierarchical_tasks(struct engine *e, struct cell *c) {
       }
 
       /* Generate the ghost tasks. */
-      if (is_hydro) {
+      if (is_with_hydro) {
         c->ghost_in =
             scheduler_addtask(s, task_type_ghost, task_subtype_none, 0,
                               /* implicit = */ 1, c, NULL);
@@ -215,14 +220,13 @@ void engine_make_hierarchical_tasks(struct engine *e, struct cell *c) {
             scheduler_addtask(s, task_type_ghost, task_subtype_none, 0,
                               /* implicit = */ 1, c, NULL);
         engine_add_ghosts(e, c, c->ghost_in, c->ghost_out);
-      }
 
 #ifdef EXTRA_HYDRO_LOOP
-      /* Generate the extra ghost task. */
-      if (is_hydro)
+        /* Generate the extra ghost task. */
         c->extra_ghost = scheduler_addtask(s, task_type_extra_ghost,
                                            task_subtype_none, 0, 0, c, NULL);
 #endif
+      }
 
       /* Cooling task */
       if (is_with_cooling) {
@@ -898,6 +902,16 @@ void engine_repartition(struct engine *e) {
   partition_repartition(e->reparttype, e->nodeID, e->nr_nodes, e->s,
                         e->sched.tasks, e->sched.nr_tasks);
 
+  /* Partitioning requires copies of the particles, so we need to reduce the
+   * memory in use to the minimum, we can free the sorting indices and the
+   * tasks as these will be regenerated at the next rebuild. */
+
+  /* Sorting indices. */
+  if (e->s->cells_top != NULL) space_free_cells(e->s);
+
+  /* Task arrays. */
+  scheduler_free_tasks(&e->sched);
+
   /* Now comes the tricky part: Exchange particles between all nodes.
      This is done in two steps, first allreducing a matrix of
      how many particles go from where to where, then re-allocating
@@ -1731,7 +1745,7 @@ void engine_make_self_gravity_tasks_mapper(void *map_data, int num_elements,
     /* If the cells is local build a self-interaction */
     scheduler_addtask(sched, task_type_self, task_subtype_grav, 0, 0, ci, NULL);
 
-    /* Deal with periodicity dependencies */
+    /* Deal with periodicity FFT task dependencies */
     const int ghost_id = cell_getid(cdim_ghost, i / 4, j / 4, k / 4);
     if (ghost_id > n_ghosts) error("Invalid ghost_id");
     if (periodic) {
@@ -1739,6 +1753,10 @@ void engine_make_self_gravity_tasks_mapper(void *map_data, int num_elements,
       ci->grav_ghost[1] = ghosts[2 * ghost_id + 1];
     }
 
+    /* Recover the multipole information */
+    struct gravity_tensors *const multi_i = ci->multipole;
+    const double CoM_i[3] = {multi_i->CoM[0], multi_i->CoM[1], multi_i->CoM[2]};
+
     /* Loop over every other cell */
     for (int ii = 0; ii < cdim[0]; ii++) {
       for (int jj = 0; jj < cdim[1]; jj++) {
@@ -1757,11 +1775,27 @@ void engine_make_self_gravity_tasks_mapper(void *map_data, int num_elements,
           /* Is that neighbour local ? */
           if (cj->nodeID != nodeID) continue;  // MATTHIEU
 
-          /* Are the cells to close for a MM interaction ? */
-          if (!gravity_multipole_accept_rebuild(ci->multipole, cj->multipole,
-                                                theta_crit_inv, periodic,
-                                                dim)) {
+          /* Recover the multipole information */
+          struct gravity_tensors *const multi_j = cj->multipole;
+
+          /* Get the distance between the CoMs */
+          double dx = CoM_i[0] - multi_j->CoM[0];
+          double dy = CoM_i[1] - multi_j->CoM[1];
+          double dz = CoM_i[2] - multi_j->CoM[2];
+
+          /* Apply BC */
+          if (periodic) {
+            dx = nearest(dx, dim[0]);
+            dy = nearest(dy, dim[1]);
+            dz = nearest(dz, dim[2]);
+          }
+          const double r2 = dx * dx + dy * dy + dz * dz;
+
+          /* Are the cells too close for a MM interaction ? */
+          if (!gravity_multipole_accept_rebuild(multi_i, multi_j,
+                                                theta_crit_inv, r2)) {
 
+            /* Ok, we need to add a direct pair calculation */
             scheduler_addtask(sched, task_type_pair, task_subtype_grav, 0, 0,
                               ci, cj);
           }
@@ -2796,8 +2830,7 @@ void engine_marktasks_mapper(void *map_data, int num_elements,
 
     /* Kick/Drift/init ? */
     if (t->type == task_type_kick1 || t->type == task_type_kick2 ||
-        t->type == task_type_drift_part || t->type == task_type_drift_gpart ||
-        t->type == task_type_init_grav) {
+        t->type == task_type_drift_gpart || t->type == task_type_init_grav) {
       if (cell_is_active(t->ci, e)) scheduler_activate(s, t);
     }
 
@@ -4517,8 +4550,12 @@ void engine_init(struct engine *e, struct space *s,
       e->runners[k].qid = k * nr_queues / e->nr_threads;
     }
 
-#ifdef WITH_VECTORIZATION
     /* Allocate particle caches. */
+    e->runners[k].ci_gravity_cache.count = 0;
+    e->runners[k].cj_gravity_cache.count = 0;
+    gravity_cache_init(&e->runners[k].ci_gravity_cache, space_splitsize);
+    gravity_cache_init(&e->runners[k].cj_gravity_cache, space_splitsize);
+#ifdef WITH_VECTORIZATION
     e->runners[k].ci_cache.count = 0;
     e->runners[k].cj_cache.count = 0;
     cache_init(&e->runners[k].ci_cache, CACHE_SIZE);
@@ -4609,8 +4646,12 @@ void engine_compute_next_snapshot_time(struct engine *e) {
 void engine_clean(struct engine *e) {
 
 #ifdef WITH_VECTORIZATION
-  for (int i = 0; i < e->nr_threads; ++i) cache_clean(&e->runners[i].ci_cache);
-  for (int i = 0; i < e->nr_threads; ++i) cache_clean(&e->runners[i].cj_cache);
+  for (int i = 0; i < e->nr_threads; ++i) {
+    cache_clean(&e->runners[i].ci_cache);
+    cache_clean(&e->runners[i].cj_cache);
+    gravity_cache_clean(&e->runners[i].ci_gravity_cache);
+    gravity_cache_clean(&e->runners[i].cj_gravity_cache);
+  }
 #endif
   free(e->runners);
   free(e->snapshotUnits);

src/gravity.c

@@ -21,9 +21,15 @@
 #include "../config.h"
 
 /* Some standard headers. */
+#include <float.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <unistd.h>
 
+#ifdef HAVE_HDF5
+#include <hdf5.h>
+#endif
+
 /* This object's header. */
 #include "gravity.h"
 
@@ -39,6 +45,256 @@ struct exact_force_data {
   double const_G;
 };
 
+#ifdef SWIFT_GRAVITY_FORCE_CHECKS
+
+/* Size of the Ewald table */
+#define Newald 64
+
+/* Components of the Ewald correction */
+static float fewald_x[Newald + 1][Newald + 1][Newald + 1];
+static float fewald_y[Newald + 1][Newald + 1][Newald + 1];
+static float fewald_z[Newald + 1][Newald + 1][Newald + 1];
+
+/* Factor used to normalize the access to the Ewald table */
+float ewald_fac;
+#endif
+
+/**
+ * @brief Allocates the memory and computes one octant of the
+ * Ewald correction table.
+ *
+ * We follow Hernquist, Bouchet & Suto, 1991, ApJS, Volume 75, p.231-240,
+ * equations (2.14a) and (2.14b) with alpha = 2. We consider all terms with
+ * |x - nL| < 4L and |h|^2 < 16.
+ *
+ * @param boxSize The side-length (L) of the volume.
+ */
+void gravity_exact_force_ewald_init(double boxSize) {
+
+#ifdef SWIFT_GRAVITY_FORCE_CHECKS
+  const ticks tic = getticks();
+  message("Computing Ewald correction table...");
+
+  /* Level of correction  (Hernquist et al. 1991)*/
+  const float alpha = 2.f;
+
+  /* some useful constants */
+  const float alpha2 = alpha * alpha;
+  const float factor_exp1 = 2.f * alpha / sqrt(M_PI);
+  const float factor_exp2 = -M_PI * M_PI / alpha2;
+  const float factor_sin = 2.f * M_PI;
+  const float boxSize_inv2 = 1.f / (boxSize * boxSize);
+
+  /* Ewald factor to access the table */
+  ewald_fac = (double)(2 * Newald) / boxSize;
+
+  /* Zero everything */
+  bzero(fewald_x, (Newald + 1) * (Newald + 1) * (Newald + 1) * sizeof(float));
+  bzero(fewald_y, (Newald + 1) * (Newald + 1) * (Newald + 1) * sizeof(float));
+  bzero(fewald_z, (Newald + 1) * (Newald + 1) * (Newald + 1) * sizeof(float));
+
+  /* Compute the values in one of the octants */
+  for (int i = 0; i <= Newald; ++i) {
+    for (int j = 0; j <= Newald; ++j) {
+      for (int k = 0; k <= Newald; ++k) {
+
+        if (i == 0 && j == 0 && k == 0) continue;
+
+        /* Distance vector */
+        const float r_x = 0.5f * ((float)i) / Newald;
+        const float r_y = 0.5f * ((float)j) / Newald;
+        const float r_z = 0.5f * ((float)k) / Newald;
+
+        /* Norm of distance vector */
+        const float r2 = r_x * r_x + r_y * r_y + r_z * r_z;
+        const float r_inv = 1.f / sqrtf(r2);
+        const float r_inv3 = r_inv * r_inv * r_inv;
+
+        /* Normal gravity potential term */
+        float f_x = r_x * r_inv3;
+        float f_y = r_y * r_inv3;
+        float f_z = r_z * r_inv3;
+
+        for (int n_i = -4; n_i <= 4; ++n_i) {
+          for (int n_j = -4; n_j <= 4; ++n_j) {
+            for (int n_k = -4; n_k <= 4; ++n_k) {
+
+              const float d_x = r_x - n_i;
+              const float d_y = r_y - n_j;
+              const float d_z = r_z - n_k;
+
+              /* Discretised distance */
+              const float r_tilde2 = d_x * d_x + d_y * d_y + d_z * d_z;
+              const float r_tilde_inv = 1.f / sqrtf(r_tilde2);
+              const float r_tilde = r_tilde_inv * r_tilde2;
+              const float r_tilde_inv3 =
+                  r_tilde_inv * r_tilde_inv * r_tilde_inv;
+
+              const float val =
+                  erfcf(alpha * r_tilde) +
+                  factor_exp1 * r_tilde * expf(-alpha2 * r_tilde2);
+
+              /* First correction term */
+              const float f = val * r_tilde_inv3;
+              f_x -= f * d_x;
+              f_y -= f * d_y;
+              f_z -= f * d_z;
+            }
+          }
+        }
+
+        for (int h_i = -4; h_i <= 4; ++h_i) {
+          for (int h_j = -4; h_j <= 4; ++h_j) {
+            for (int h_k = -4; h_k <= 4; ++h_k) {
+
+              const float h2 = h_i * h_i + h_j * h_j + h_k * h_k;
+
+              const float h2_inv = 1.f / (h2 + FLT_MIN);
+              const float h_dot_x = h_i * r_x + h_j * r_y + h_k * r_z;
+
+              const float val = 2.f * h2_inv * expf(h2 * factor_exp2) *
+                                sinf(factor_sin * h_dot_x);
+
+              /* Second correction term */
+              f_x -= val * h_i;
+              f_y -= val * h_j;
+              f_z -= val * h_k;
+            }
+          }
+        }
+
+        /* Save back to memory */
+        fewald_x[i][j][k] = f_x;
+        fewald_y[i][j][k] = f_y;
+        fewald_z[i][j][k] = f_z;
+      }
+    }
+  }
+
+/* Dump the Ewald table to a file */
+#ifdef HAVE_HDF5
+  hid_t h_file =
+      H5Fcreate("Ewald.hdf5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
+  if (h_file < 0) error("Error while opening file for Ewald dump.");
+
+  /* Create dataspace */
+  hsize_t dim[3] = {Newald + 1, Newald + 1, Newald + 1};
+  hid_t h_space = H5Screate_simple(3, dim, NULL);
+  hid_t h_data;
+  h_data = H5Dcreate(h_file, "Ewald_x", H5T_NATIVE_FLOAT, h_space, H5P_DEFAULT,
+                     H5P_DEFAULT, H5P_DEFAULT);
+  H5Dwrite(h_data, H5T_NATIVE_FLOAT, h_space, H5S_ALL, H5P_DEFAULT,
+           &(fewald_x[0][0][0]));
+  H5Dclose(h_data);
+  h_data = H5Dcreate(h_file, "Ewald_y", H5T_NATIVE_FLOAT, h_space, H5P_DEFAULT,
+                     H5P_DEFAULT, H5P_DEFAULT);
+  H5Dwrite(h_data, H5T_NATIVE_FLOAT, h_space, H5S_ALL, H5P_DEFAULT,
+           &(fewald_y[0][0][0]));
+  H5Dclose(h_data);
+  h_data = H5Dcreate(h_file, "Ewald_z", H5T_NATIVE_FLOAT, h_space, H5P_DEFAULT,
+                     H5P_DEFAULT, H5P_DEFAULT);
+  H5Dwrite(h_data, H5T_NATIVE_FLOAT, h_space, H5S_ALL, H5P_DEFAULT,
+           &(fewald_z[0][0][0]));
+  H5Dclose(h_data);
+  H5Sclose(h_space);
+  H5Fclose(h_file);
+#endif
+
+  /* Apply the box-size correction */
+  for (int i = 0; i <= Newald; ++i) {
+    for (int j = 0; j <= Newald; ++j) {
+      for (int k = 0; k <= Newald; ++k) {
+        fewald_x[i][j][k] *= boxSize_inv2;
+        fewald_y[i][j][k] *= boxSize_inv2;
+        fewald_z[i][j][k] *= boxSize_inv2;
+      }
+    }
+  }
+
+  /* Say goodbye */
+  message("Ewald correction table computed (took %.3f %s). ",
+          clocks_from_ticks(getticks() - tic), clocks_getunit());
+#else
+  error("Gravity checking function called without the corresponding flag.");