Don't initialise multipoles if they don't exist.

src/multipole.h

@@ -289,31 +289,30 @@ INLINE static void multipole_M2M(struct multipole *m_a,
  * @param pos_b The position of the multipole.
  * @param periodic Is the calculation periodic ?
  */
-/* INLINE static void multipole_M2L(struct field_tensors *l_a, */
-/*                                  const struct multipole m_b, */
-/*                                  const double pos_a[3], const double
- * pos_b[3], */
-/*                                  int periodic) { */
-
-/*   /\* double dx, dy, dz; *\/ */
-/*   /\* if (periodic) { *\/ */
-/*   /\*   dx = box_wrap(pos_a[0] - pos_b[0], 0., 1.); *\/ */
-/*   /\*   dy = box_wrap(pos_a[1] - pos_b[1], 0., 1.); *\/ */
-/*   /\*   dz = box_wrap(pos_a[2] - pos_b[2], 0., 1.); *\/ */
-/*   /\* } else { *\/ */
-/*   /\*   dx = pos_a[0] - pos_b[0]; *\/ */
-/*   /\*   dy = pos_a[1] - pos_b[1]; *\/ */
-/*   /\*   dz = pos_a[2] - pos_b[2]; *\/ */
-/*   /\* } *\/ */
-/*   /\* const double r2 = dx * dx + dy * dy + dz * dz; *\/ */
-
-/*   /\* const double r_inv = 1. / sqrt(r2); *\/ */
-
-/*   /\* /\\* 1st order multipole term *\\/ *\/ */
-/*   /\* l_a->x.F_000 =  D_100(dx, dy, dz, r_inv); *\/ */
-/*   /\* l_a->y.F_000 =  D_010(dx, dy, dz, r_inv); *\/ */
-/*   /\* l_a->z.F_000 =  D_001(dx, dy, dz, r_inv); *\/ */
-/* } */
+INLINE static void multipole_M2L(struct gravity_tensors *l_a,
+                                 const struct multipole *m_b,
+                                 const double pos_a[3], const double  pos_b[3],
+                                 int periodic) {
+
+  double dx, dy, dz;
+  if (periodic) {
+    dx = box_wrap(pos_a[0] - pos_b[0], 0., 1.);
+    dy = box_wrap(pos_a[1] - pos_b[1], 0., 1.);
+    dz = box_wrap(pos_a[2] - pos_b[2], 0., 1.);
+  } else {
+    dx = pos_a[0] - pos_b[0];
+    dy = pos_a[1] - pos_b[1];
+    dz = pos_a[2] - pos_b[2];
+  }
+  const double r2 = dx * dx + dy * dy + dz * dz;
+
+  const double r_inv = 1. / sqrt(r2);
+
+  /* 1st order multipole term */
+  l_a->a_x.F_000 =  D_100(dx, dy, dz, r_inv) * m_b->mass;
+  l_a->a_y.F_000 =  D_010(dx, dy, dz, r_inv) * m_b->mass;
+  l_a->a_z.F_000 =  D_001(dx, dy, dz, r_inv) * m_b->mass;
+}
 
 #if 0
 

src/runner.c

@@ -496,7 +496,8 @@ void runner_do_init(struct runner *r, struct cell *c, int timer) {
   if (!cell_is_active(c, e)) return;
 
   /* Reset the gravity acceleration tensors */
-  if (c->multipole) multipole_init(c->multipole);
+  if (e->policy & engine_policy_self_gravity)
+    multipole_init(c->multipole);
 
   /* Recurse? */
   if (c->split) {

src/runner_doiact_grav.h

@@ -53,6 +53,42 @@ void runner_do_grav_up(struct runner *r, struct cell *c) {
   /* } */
 }
 
+/**
+ * @brief Computes the interaction of the field tensor in a cell with the
+ * multipole of another cell.
+ *
+ * @param r The #runner.
+ * @param ci The #cell with field tensor to interact.
+ * @param cj The #cell with the multipole.
+ */
+__attribute__((always_inline)) INLINE static void runner_dopair_grav_mm(
+    const struct runner *r, const struct cell *restrict ci,
+    const struct cell *restrict cj) {
+
+  const struct engine *e = r->e;
+  const int periodic = e->s->periodic;
+  const struct multipole *multi_j = &cj->multipole->m_pole;
+  //const float a_smooth = e->gravity_properties->a_smooth;
+  //const float rlr_inv = 1. / (a_smooth * ci->super->width[0]);
+
+  TIMER_TIC;
+
+#ifdef SWIFT_DEBUG_CHECKS
+  if (multi_j->mass == 0.0)
+    error("Multipole does not seem to have been set.");
+#endif
+
+  /* Anything to do here? */
+  if (!cell_is_active(ci, e)) return;
+
+  multipole_M2L(ci->multipole, multi_j, ci->multipole->CoM, cj->multipole->CoM,
+		periodic);
+
+  
+  TIMER_TOC(timer_dopair_grav_mm);
+}
+
+
 /**
  * @brief Computes the interaction of all the particles in a cell with the
  * multipole of another cell.
@@ -541,7 +577,7 @@ static void runner_do_grav_long_range(struct runner *r, struct cell *ci,
 
     // if (r2 > max_d2) continue;
 
-    if (!cell_are_neighbours(ci, cj)) runner_dopair_grav_pm(r, ci, cj);
+    if (!cell_are_neighbours(ci, cj)) runner_dopair_grav_mm(r, ci, cj);
   }
 }
 

src/timers.h

@@ -46,6 +46,7 @@ enum {
   timer_dopair_gradient,
   timer_dopair_force,
   timer_dopair_grav_pm,
+  timer_dopair_grav_mm,
   timer_dopair_grav_pp,
   timer_dograv_external,
   timer_dosource,