Do not store the dipole terms since they are always zero.

src/cell.c

@@ -2283,11 +2283,6 @@ void cell_make_multipoles(struct cell *c, integertime_t ti_current,
     /* Take minimum of both limits */
     c->grav.multipole->r_max = min(r_max, sqrt(dx * dx + dy * dy + dz * dz));
 
-    /* We know the first-order multipole (dipole) is 0. */
-    c->grav.multipole->m_pole.M_100 = 0.f;
-    c->grav.multipole->m_pole.M_010 = 0.f;
-    c->grav.multipole->m_pole.M_001 = 0.f;
-
     /* Compute the multipole power */
     gravity_multipole_compute_power(&c->grav.multipole->m_pole);
 

src/multipole_struct.h

@@ -132,8 +132,8 @@ struct multipole {
 
 #if SELF_GRAVITY_MULTIPOLE_ORDER > 0
 
-  /* 1st order terms */
-  float M_100, M_010, M_001;
+  /* 1st order terms (all 0 since we expand around CoM) */
+  // float M_100, M_010, M_001;
 
 #endif
 #if SELF_GRAVITY_MULTIPOLE_ORDER > 1

src/space.c

@@ -3659,11 +3659,6 @@ void space_split_recursive(struct space *s, struct cell *c,
       c->grav.multipole->CoM_rebuild[1] = c->grav.multipole->CoM[1];
       c->grav.multipole->CoM_rebuild[2] = c->grav.multipole->CoM[2];
 
-      /* We know the first-order multipole (dipole) is 0. */
-      c->grav.multipole->m_pole.M_100 = 0.f;
-      c->grav.multipole->m_pole.M_010 = 0.f;
-      c->grav.multipole->m_pole.M_001 = 0.f;
-
       /* Compute the multipole power */
       gravity_multipole_compute_power(&c->grav.multipole->m_pole);