Initial implementation of mass-dependent multipole acceptance criterion

examples/EAGLE_6/eagle_6.yml

@@ -30,7 +30,7 @@ Statistics:
 Gravity:
   eta:                   0.025    # Constant dimensionless multiplier for time integration.
   theta:                 0.7      # Opening angle (Multipole acceptance criterion)
-  epsilon:               0.0001   # Softening length (in internal units).
+  epsilon:               0.001   # Softening length (in internal units).
   
 # Parameters for the hydrodynamics scheme
 SPH:

src/cell.c

@@ -1679,7 +1679,7 @@ void cell_activate_subcell_grav_tasks(struct cell *ci, struct cell *cj,
   const struct engine *e = sp->e;
   const int periodic = sp->periodic;
   const double dim[3] = {sp->dim[0], sp->dim[1], sp->dim[2]};
-  const double theta_crit = e->gravity_properties->theta_crit;
+  const double theta_crit2 = e->gravity_properties->theta_crit2;
 
   /* Self interaction? */
   if (cj == NULL) {
@@ -1733,7 +1733,7 @@ void cell_activate_subcell_grav_tasks(struct cell *ci, struct cell *cj,
     const double r2 = dx * dx + dy * dy + dz * dz;
 
     /* Can we use multipoles ? */
-    if (gravity_multipole_accept(multi_i, multi_j, theta_crit, r2)) {
+    if (gravity_multipole_accept(multi_i, multi_j, theta_crit2, r2)) {
 
       /* Ok, no need to drift anything */
       return;

src/engine.c

@@ -1726,7 +1726,7 @@ void engine_make_self_gravity_tasks_mapper(void *map_data, int num_elements,
   const int cdim[3] = {s->cdim[0], s->cdim[1], s->cdim[2]};
   const int cdim_ghost[3] = {s->cdim[0] / 4 + 1, s->cdim[1] / 4 + 1,
                              s->cdim[2] / 4 + 1};
-  const double theta_crit = e->gravity_properties->theta_crit;
+  const double theta_crit2 = e->gravity_properties->theta_crit2;
   struct cell *cells = s->cells_top;
   const int n_ghosts = cdim_ghost[0] * cdim_ghost[1] * cdim_ghost[2] * 2;
 
@@ -1798,7 +1798,7 @@ void engine_make_self_gravity_tasks_mapper(void *map_data, int num_elements,
           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,
+          if (!gravity_multipole_accept_rebuild(multi_i, multi_j, theta_crit2,
                                                 r2)) {
 
             /* Ok, we need to add a direct pair calculation */

src/gravity_properties.c

@@ -52,6 +52,8 @@ void gravity_props_init(struct gravity_props *p,
 
   /* Opening angle */
   p->theta_crit = parser_get_param_double(params, "Gravity:theta");
+  if (p->theta_crit >= 1.) error("Theta too large. FMM won't converge.");
+  p->theta_crit2 = p->theta_crit * p->theta_crit;
   p->theta_crit_inv = 1. / p->theta_crit;
 
   /* Softening lengths */

src/gravity_properties.h

@@ -51,6 +51,9 @@ struct gravity_props {
   /*! Tree opening angle (Multipole acceptance criterion) */
   double theta_crit;
 
+  /*! Square of opening angle */
+  double theta_crit2;
+
   /*! Inverse of opening angle */
   double theta_crit_inv;
 

src/multipole.h

@@ -234,6 +234,7 @@ INLINE static void gravity_drift(struct gravity_tensors *m, double dt) {
  * @brief Zeroes all the fields of a field tensor
  *
  * @param l The field tensor.
+ * @param ti_current The current (integer) time (for debugging only).
  */
 INLINE static void gravity_field_tensors_init(struct grav_tensor *l,
                                               integertime_t ti_current) {
@@ -246,7 +247,7 @@ INLINE static void gravity_field_tensors_init(struct grav_tensor *l,
 }
 
 /**
- * @brief Adds field tensrs to other ones (i.e. does la += lb).
+ * @brief Adds a field tensor to another one (i.e. does la += lb).
  *
  * @param la The gravity tensors to add to.
  * @param lb The gravity tensors to add.
@@ -2174,6 +2175,9 @@ INLINE static void gravity_M2L(struct grav_tensor *l_b,
     l_b->F_102 += m_a->M_000 * D_soft_102(dx, dy, dz, r, eps_inv);
     l_b->F_012 += m_a->M_000 * D_soft_012(dx, dy, dz, r, eps_inv);
     l_b->F_111 += m_a->M_000 * D_soft_111(dx, dy, dz, r, eps_inv);
+#endif
+#if SELF_GRAVITY_MULTIPOLE_ORDER > 5
+#error "Missing implementation for order >5"
 #endif
   }
 }
@@ -2654,22 +2658,24 @@ INLINE static void gravity_L2P(const struct grav_tensor *lb,
  *
  * @param ma The #multipole of the first #cell.
  * @param mb The #multipole of the second #cell.
- * @param theta_crit The critical opening angle.
+ * @param theta_crit2 The square of the critical opening angle.
  * @param r2 Square of the distance (periodically wrapped) between the
  * multipoles.
  */
 __attribute__((always_inline)) INLINE static int
 gravity_multipole_accept_rebuild(const struct gravity_tensors *const ma,
                                  const struct gravity_tensors *const mb,
-                                 double theta_crit, double r2) {
+                                 double theta_crit2, double r2) {
 
-  const double r_crit_a = ma->r_max_rebuild * theta_crit;
-  const double r_crit_b = mb->r_max_rebuild * theta_crit;
+  const double r_crit_a = ma->r_max_rebuild;
+  const double r_crit_b = mb->r_max_rebuild;
+  const double size = r_crit_a + r_crit_b;
+  const double size2 = size * size;
 
   // MATTHIEU: Make this mass-dependent ?
 
   /* Multipole acceptance criterion (Dehnen 2002, eq.10) */
-  return (r2 > (r_crit_a + r_crit_b) * (r_crit_a + r_crit_b));
+  return (r2 * theta_crit2 > size2);
 }
 
 /**
@@ -2681,21 +2687,23 @@ gravity_multipole_accept_rebuild(const struct gravity_tensors *const ma,
  *
  * @param ma The #multipole of the first #cell.
  * @param mb The #multipole of the second #cell.
- * @param theta_crit The critical opening angle.
+ * @param theta_crit2 The square of the critical opening angle.
  * @param r2 Square of the distance (periodically wrapped) between the
  * multipoles.
  */
 __attribute__((always_inline)) INLINE static int gravity_multipole_accept(
     const struct gravity_tensors *const ma,
-    const struct gravity_tensors *const mb, double theta_crit, double r2) {
+    const struct gravity_tensors *const mb, double theta_crit2, double r2) {
 
-  const double r_crit_a = ma->r_max * theta_crit;
-  const double r_crit_b = mb->r_max * theta_crit;
+  const double r_crit_a = ma->r_max;
+  const double r_crit_b = mb->r_max;
+  const double size = r_crit_a + r_crit_b;
+  const double size2 = size * size;
 
   // MATTHIEU: Make this mass-dependent ?
 
   /* Multipole acceptance criterion (Dehnen 2002, eq.10) */
-  return (r2 > (r_crit_a + r_crit_b) * (r_crit_a + r_crit_b));
+  return (r2 * theta_crit2 > size2);
 }
 
 #endif /* SWIFT_MULTIPOLE_H */

src/runner_doiact_grav.h

@@ -1412,7 +1412,7 @@ void runner_dopair_grav(struct runner *r, struct cell *ci, struct cell *cj,
   const double cell_width = s->width[0];
   const double dim[3] = {s->dim[0], s->dim[1], s->dim[2]};
   const struct gravity_props *props = e->gravity_properties;
-  const double theta_crit = props->theta_crit;
+  const double theta_crit2 = props->theta_crit2;
   const double max_distance = props->a_smooth * props->r_cut_max * cell_width;
   const double max_distance2 = max_distance * max_distance;
 
@@ -1473,7 +1473,7 @@ void runner_dopair_grav(struct runner *r, struct cell *ci, struct cell *cj,
    * option... */
 
   /* Can we use M-M interactions ? */
-  if (gravity_multipole_accept(multi_i, multi_j, theta_crit, r2)) {
+  if (gravity_multipole_accept(multi_i, multi_j, theta_crit2, r2)) {
 
     /* MATTHIEU: make a symmetric M-M interaction function ! */
     runner_dopair_grav_mm(r, ci, cj);
@@ -1638,7 +1638,7 @@ void runner_do_grav_long_range(struct runner *r, struct cell *ci, int timer) {
   const int periodic = s->periodic;
   const double cell_width = s->width[0];
   const double dim[3] = {s->dim[0], s->dim[1], s->dim[2]};
-  const double theta_crit = props->theta_crit;
+  const double theta_crit2 = props->theta_crit2;
   const double max_distance = props->a_smooth * props->r_cut_max * cell_width;
   const double max_distance2 = max_distance * max_distance;
 
@@ -1697,7 +1697,7 @@ void runner_do_grav_long_range(struct runner *r, struct cell *ci, int timer) {
     }
 
     /* Check the multipole acceptance criterion */
-    if (gravity_multipole_accept(multi_i, multi_j, theta_crit, r2)) {
+    if (gravity_multipole_accept(multi_i, multi_j, theta_crit2, r2)) {
 
       /* Go for a (non-symmetric) M-M calculation */
       runner_dopair_grav_mm(r, ci, cj);
@@ -1720,7 +1720,7 @@ void runner_do_grav_long_range(struct runner *r, struct cell *ci, int timer) {
       const double r2_rebuild = dx * dx + dy * dy + dz * dz;
 
       /* Is the criterion violated now but was OK at the last rebuild ? */
-      if (gravity_multipole_accept_rebuild(multi_i, multi_j, theta_crit,
+      if (gravity_multipole_accept_rebuild(multi_i, multi_j, theta_crit2,
                                            r2_rebuild)) {
 
         /* Alright, we have to take charge of that pair in a different way. */