Use the CoM at rebuild time and not the actual CoM in...

Use the CoM at rebuild time and not the actual CoM in cell_can_use_pair_mm_rebuild() (as the documentation actually suggests....)

src/cell.c

@@ -3077,6 +3077,9 @@ int cell_can_use_pair_mm(const struct cell *ci, const struct cell *cj,
 /**
  * @brief Can we use the MM interactions fo a given pair of cells?
  *
+ * This function uses the information gathered in the multipole at rebuild
+ * time and not the current position and radius of the multipole.
+ *
  * @param ci The first #cell.
  * @param cj The second #cell.
  * @param e The #engine.
@@ -3096,32 +3099,32 @@ int cell_can_use_pair_mm_rebuild(const struct cell *ci, const struct cell *cj,
 
 #ifdef SWIFT_DEBUG_CHECKS
 
-  if (multi_i->CoM[0] < ci->loc[0] ||
-      multi_i->CoM[0] > ci->loc[0] + ci->width[0])
+  if (multi_i->CoM_rebuild[0] < ci->loc[0] ||
+      multi_i->CoM_rebuild[0] > ci->loc[0] + ci->width[0])
     error("Invalid multipole position ci");
-  if (multi_i->CoM[1] < ci->loc[1] ||
-      multi_i->CoM[1] > ci->loc[1] + ci->width[1])
+  if (multi_i->CoM_rebuild[1] < ci->loc[1] ||
+      multi_i->CoM_rebuild[1] > ci->loc[1] + ci->width[1])
     error("Invalid multipole position ci");
-  if (multi_i->CoM[2] < ci->loc[2] ||
-      multi_i->CoM[2] > ci->loc[2] + ci->width[2])
+  if (multi_i->CoM_rebuild[2] < ci->loc[2] ||
+      multi_i->CoM_rebuild[2] > ci->loc[2] + ci->width[2])
     error("Invalid multipole position ci");
 
-  if (multi_j->CoM[0] < cj->loc[0] ||
-      multi_j->CoM[0] > cj->loc[0] + cj->width[0])
+  if (multi_j->CoM_rebuild[0] < cj->loc[0] ||
+      multi_j->CoM_rebuild[0] > cj->loc[0] + cj->width[0])
     error("Invalid multipole position cj");
-  if (multi_j->CoM[1] < cj->loc[1] ||
-      multi_j->CoM[1] > cj->loc[1] + cj->width[1])
+  if (multi_j->CoM_rebuild[1] < cj->loc[1] ||
+      multi_j->CoM_rebuild[1] > cj->loc[1] + cj->width[1])
     error("Invalid multipole position cj");
-  if (multi_j->CoM[2] < cj->loc[2] ||
-      multi_j->CoM[2] > cj->loc[2] + cj->width[2])
+  if (multi_j->CoM_rebuild[2] < cj->loc[2] ||
+      multi_j->CoM_rebuild[2] > cj->loc[2] + cj->width[2])
     error("Invalid multipole position cj");
 
 #endif
 
   /* Get the distance between the CoMs */
-  double dx = multi_i->CoM[0] - multi_j->CoM[0];
-  double dy = multi_i->CoM[1] - multi_j->CoM[1];
-  double dz = multi_i->CoM[2] - multi_j->CoM[2];
+  double dx = multi_i->CoM_rebuild[0] - multi_j->CoM_rebuild[0];
+  double dy = multi_i->CoM_rebuild[1] - multi_j->CoM_rebuild[1];
+  double dz = multi_i->CoM_rebuild[2] - multi_j->CoM_rebuild[2];
 
   /* Apply BC */
   if (periodic) {
@@ -3131,5 +3134,6 @@ int cell_can_use_pair_mm_rebuild(const struct cell *ci, const struct cell *cj,
   }
   const double r2 = dx * dx + dy * dy + dz * dz;
 
-  return gravity_M2L_accept(multi_i->r_max, multi_j->r_max, theta_crit2, r2);
+  return gravity_M2L_accept(multi_i->r_max_rebuild, multi_j->r_max_rebuild,
+                            theta_crit2, r2);
 }