Potential forces don't contain Newton's constant any more.

src/cell.c

@@ -725,7 +725,8 @@ int cell_are_neighbours(const struct cell *restrict ci,
 #endif
 
   /* Maximum allowed distance */
-  const double min_dist = 1.2 * ci->width[0]; /* 1.2 accounts for rounding errors */
+  const double min_dist =
+      1.2 * ci->width[0]; /* 1.2 accounts for rounding errors */
 
   /* (Manhattan) Distance between the cells */
   for (int k = 0; k < 3; k++) {

src/potentials.c

@@ -47,7 +47,7 @@ void potential_init(const struct swift_params* parameter_file,
   potential->point_mass.mass =
       parser_get_param_double(parameter_file, "PointMass:mass");
   potential->point_mass.timestep_mult =
-      parser_get_param_double(parameter_file, "PointMass:timestep_mult");
+      parser_get_param_float(parameter_file, "PointMass:timestep_mult");
 
 #endif /* EXTERNAL_POTENTIAL_POINTMASS */
 
@@ -61,7 +61,7 @@ void potential_init(const struct swift_params* parameter_file,
       parser_get_param_double(parameter_file, "IsothermalPotential:position_z");
   potential->isothermal_potential.vrot =
       parser_get_param_double(parameter_file, "IsothermalPotential:vrot");
-  potential->isothermal_potential.timestep_mult = parser_get_param_double(
+  potential->isothermal_potential.timestep_mult = parser_get_param_float(
       parameter_file, "IsothermalPotential:timestep_mult");
 
 #endif /* EXTERNAL_POTENTIAL_ISOTHERMALPOTENTIAL */

src/potentials.h

@@ -42,7 +42,7 @@ struct external_potential {
   struct {
     double x, y, z;
     double mass;
-    double timestep_mult;
+    float timestep_mult;
   } point_mass;
 #endif
 
@@ -50,7 +50,7 @@ struct external_potential {
   struct {
     double x, y, z;
     double vrot;
-    double timestep_mult;
+    float timestep_mult;
   } isothermal_potential;
 #endif
 };
@@ -95,6 +95,8 @@ external_gravity_isothermalpotential_timestep(
  * @brief Computes the gravitational acceleration of a particle due to a point
  * mass
  *
+ * Note that the accelerations are multiplied by Newton's G constant later on.
+ *
  * @param potential The #external_potential used in the run.
  * @param phys_const The physical constants in internal units.
  * @param g Pointer to the g-particle data.
@@ -104,15 +106,19 @@ external_gravity_isothermalpotential(const struct external_potential* potential,
                                      const struct phys_const* const phys_const,
                                      struct gpart* g) {
 
+  const float G_newton = phys_const->const_newton_G;
+
   const float dx = g->x[0] - potential->isothermal_potential.x;
   const float dy = g->x[1] - potential->isothermal_potential.y;
   const float dz = g->x[2] - potential->isothermal_potential.z;
   const float rinv2 = 1.f / (dx * dx + dy * dy + dz * dz);
 
   const double vrot = potential->isothermal_potential.vrot;
-  g->a_grav[0] += -vrot * vrot * rinv2 * dx;
-  g->a_grav[1] += -vrot * vrot * rinv2 * dy;
-  g->a_grav[2] += -vrot * vrot * rinv2 * dz;
+  const double term = -vrot * vrot * rinv2 / G_newton;
+
+  g->a_grav[0] += term * dx;
+  g->a_grav[1] += term * dy;
+  g->a_grav[2] += term * dz;
   // error(" %f %f %f %f", vrot, rinv2, dx, g->a_grav[0]);
 }
 

src/runner_doiact_grav.h

@@ -145,7 +145,8 @@ __attribute__((always_inline)) INLINE static void runner_dopair_grav_pp(
 
 #ifdef SWIFT_DEBUG_CHECKS
   if (ci->width[0] != cj->width[0])  // MATTHIEU sanity check
-    error("Non matching cell sizes !! h_i=%f h_j=%f", ci->width[0], cj->width[0]);
+    error("Non matching cell sizes !! h_i=%f h_j=%f", ci->width[0],
+          cj->width[0]);
 #endif
 
   /* Anything to do here? */
@@ -253,8 +254,8 @@ __attribute__((always_inline)) INLINE static void runner_doself_grav_pp(
 
     if (gp->id_or_neg_offset == ICHECK)
       message("id=%lld loc=[ %f %f %f ] size= %f count= %d",
-              gp->id_or_neg_offset, c->loc[0], c->loc[1], c->loc[2], c->width[0],
-              c->gcount);
+              gp->id_or_neg_offset, c->loc[0], c->loc[1], c->loc[2],
+              c->width[0], c->gcount);
   }
 #endif
 
@@ -325,7 +326,8 @@ static void runner_dopair_grav(struct runner *r, struct cell *ci,
 
   /* Bad stuff will happen if cell sizes are different */
   if (ci->width[0] != cj->width[0])
-    error("Non matching cell sizes !! h_i=%f h_j=%f", ci->width[0], cj->width[0]);
+    error("Non matching cell sizes !! h_i=%f h_j=%f", ci->width[0],
+          cj->width[0]);
 
   /* Sanity check */
   if (ci == cj)
@@ -336,10 +338,11 @@ static void runner_dopair_grav(struct runner *r, struct cell *ci,
   /* Are the cells direct neighbours? */
   if (!cell_are_neighbours(ci, cj))
     error(
-        "Non-neighbouring cells ! ci->x=[%f %f %f] ci->width=%f cj->loc=[%f %f %f] "
+        "Non-neighbouring cells ! ci->x=[%f %f %f] ci->width=%f cj->loc=[%f %f "
+        "%f] "
         "cj->width=%f",
-        ci->loc[0], ci->loc[1], ci->loc[2], ci->width[0], cj->loc[0], cj->loc[1],
-        cj->loc[2], cj->width[0]);
+        ci->loc[0], ci->loc[1], ci->loc[2], ci->width[0], cj->loc[0],
+        cj->loc[1], cj->loc[2], cj->width[0]);
 
 #endif
 
@@ -488,7 +491,8 @@ static void runner_do_grav_mm(struct runner *r, struct cell *ci, int timer) {
   struct cell *cells = e->s->cells;
   const int nr_cells = e->s->nr_cells;
   const int ti_current = e->ti_current;
-  const double max_d = const_gravity_a_smooth * const_gravity_r_cut * ci->width[0];
+  const double max_d =
+      const_gravity_a_smooth * const_gravity_r_cut * ci->width[0];
   const double max_d2 = max_d * max_d;
   const double pos_i[3] = {ci->loc[0], ci->loc[1], ci->loc[2]};
 

tests/testFFT.c

@@ -134,14 +134,14 @@ int main() {
 
   memcpy(forcegrid, workspace + (sendmin - meshmin[0]) * dimy * dimz,
          (sendmax - sendmin + 1) * dimy * dimz * sizeof(double));
-  
+
   /* for (size_t i = 0; i < fft_size; ++i) */
   /*   if (forcegrid[i] != workspace[i]) error("wrong"); */
 
   /* Prepare the density grid */
   double* rhogrid = fftw_malloc(fft_size * sizeof(double));
   bzero(rhogrid, fft_size * sizeof(double));
-  
+
   /* Now get the density */
   for (size_t slab_x = recvmin; slab_x <= recvmax; slab_x++) {
 
@@ -169,18 +169,16 @@ int main() {
   /*   } */
   /* } */
 
-
   /* FFT of the density field */
   fftw_complex* fftgrid = fftw_malloc(fft_size * sizeof(fftw_complex));
-  fftw_plan plan_forward = fftw_plan_dft_r2c_3d(PMGRID, PMGRID, PMGRID, rhogrid, fftgrid, FFTW_ESTIMATE);
+  fftw_plan plan_forward = fftw_plan_dft_r2c_3d(PMGRID, PMGRID, PMGRID, rhogrid,
+                                                fftgrid, FFTW_ESTIMATE);
   fftw_execute(plan_forward);
 
-
-  for(size_t i = 0; i < 640; i++) {
+  for (size_t i = 0; i < 640; i++) {
     message("workspace[%zd]= %f", i, fftgrid[i][0]);
   }
-  
-  
+
   /* Clean-up */
   fftw_destroy_plan(plan_forward);
   fftw_free(forcegrid);