Implement an optional minimal smoothing length based on the softening of the particle

examples/EAGLE_100/eagle_100.yml

@@ -49,6 +49,7 @@ Gravity:
 # Parameters for the hydrodynamics scheme
 SPH:
   resolution_eta:        1.2348   # Target smoothing length in units of the mean inter-particle separation (1.2348 == 48Ngbs with the cubic spline kernel).
+  h_min_ratio:           0.1      # Minimal smoothing in units of softening.
   CFL_condition:         0.1      # Courant-Friedrich-Levy condition for time integration.
   minimal_temperature:   100      # (internal units)
 

examples/EAGLE_12/eagle_12.yml

@@ -47,6 +47,7 @@ Gravity:
 # Parameters for the hydrodynamics scheme
 SPH:
   resolution_eta:        1.2348   # Target smoothing length in units of the mean inter-particle separation (1.2348 == 48Ngbs with the cubic spline kernel).
+  h_min_ratio:           0.1      # Minimal smoothing in units of softening.
   CFL_condition:         0.1      # Courant-Friedrich-Levy condition for time integration.
   minimal_temperature:   100      # (internal units)
 

examples/EAGLE_25/eagle_25.yml

@@ -54,6 +54,7 @@ Gravity:
 # Parameters for the hydrodynamics scheme
 SPH:
   resolution_eta:        1.2348   # Target smoothing length in units of the mean inter-particle separation (1.2348 == 48Ngbs with the cubic spline kernel).
+  h_min_ratio:           0.1      # Minimal smoothing in units of softening.
   CFL_condition:         0.1      # Courant-Friedrich-Levy condition for time integration.
   minimal_temperature:   100      # (internal units)
 

examples/EAGLE_50/eagle_50.yml

@@ -49,6 +49,7 @@ Gravity:
 # Parameters for the hydrodynamics scheme
 SPH:
   resolution_eta:        1.2348   # Target smoothing length in units of the mean inter-particle separation (1.2348 == 48Ngbs with the cubic spline kernel).
+  h_min_ratio:           0.1      # Minimal smoothing in units of softening.
   CFL_condition:         0.1      # Courant-Friedrich-Levy condition for time integration.
   minimal_temperature:   100      # (internal units)
 

examples/EAGLE_6/eagle_6.yml

@@ -58,6 +58,7 @@ Gravity:
 # Parameters for the hydrodynamics scheme
 SPH:
   resolution_eta:        1.2348   # Target smoothing length in units of the mean inter-particle separation (1.2348 == 48Ngbs with the cubic spline kernel).
+  h_min_ratio:           0.1      # Minimal smoothing in units of softening.
   CFL_condition:         0.1      # Courant-Friedrich-Levy condition for time integration.
   minimal_temperature:   100      # (internal units)
 

examples/IsolatedGalaxy_starformation/isolated_galaxy.yml

@@ -42,13 +42,10 @@ InitialConditions:
 SPH:
   resolution_eta:        1.2348   # Target smoothing length in units of the mean inter-particle separation (1.2348 == 48Ngbs with the cubic spline kernel).
   CFL_condition:         0.1      # Courant-Friedrich-Levy condition for time integration.
-  h_tolerance:           1e-4     # (Optional) Relative accuracy of the Netwon-Raphson scheme for the smoothing lengths.
-  h_max:                 10.      # (Optional) Maximal allowed smoothing length in internal units. Defaults to FLT_MAX if unspecified.
-  max_volume_change:     1.4      # (Optional) Maximal allowed change of kernel volume over one time-step.
-  max_ghost_iterations:  30       # (Optional) Maximal number of iterations allowed to converge towards the smoothing length.
-  minimal_temperature:   100        # (Optional) Minimal temperature (in internal units) allowed for the gas particles. Value is ignored if set to 0.
-  H_ionization_temperature: 1e4   # (Optional) Temperature of the transition from neutral to ionized Hydrogen for primoridal gas.
+  h_min_ratio:           0.1      # Minimal smoothing in units of softening.
+  h_max:                 10.
 
+# Standard EAGLE cooling options
 EAGLECooling:
   dir_name:                ./coolingtables/  # Location of the Wiersma+08 cooling tables
   H_reion_z:               11.5              # Redshift of Hydrogen re-ionization

examples/SantaBarbara/santa_barbara.yml

@@ -46,6 +46,7 @@ Gravity:
 # Parameters of the hydro scheme
 SPH:
   resolution_eta:      1.2348   # "48 Ngb" with the cubic spline kernel
+  h_min_ratio:         0.1
   CFL_condition:       0.1
   initial_temperature: 1200.    # (1 + z_ini)^2 * 2.72K
   minimal_temperature: 100.

examples/SantaBarbara_low/santa_barbara.yml

@@ -47,6 +47,7 @@ Gravity:
 SPH:
   resolution_eta:      1.2348   # "48 Ngb" with the cubic spline kernel
   CFL_condition:       0.1
+  h_min_ratio:         0.1
   initial_temperature: 1200.    # (1 + z_ini)^2 * 2.72K
   minimal_temperature: 100.
 

examples/SmallCosmoVolume/small_cosmo_volume.yml

@@ -30,6 +30,7 @@ Gravity:
 # Parameters of the hydro scheme
 SPH:
   resolution_eta:      1.2348   # "48 Ngb" with the cubic spline kernel
+  h_min_ratio:         0.1
   CFL_condition:       0.1
   initial_temperature: 7075.    # (1 + z_ini)^2 * 2.72K
   minimal_temperature: 100.

examples/SmallCosmoVolume_VELOCIraptor/small_cosmo_volume.yml

@@ -30,6 +30,7 @@ Gravity:
 # Parameters of the hydro scheme
 SPH:
   resolution_eta:      1.2348   # "48 Ngb" with the cubic spline kernel
+  h_min_ratio:         0.1
   CFL_condition:       0.1
   initial_temperature: 7075.    # (1 + z_ini)^2 * 2.72K
   minimal_temperature: 100.

examples/SmallCosmoVolume_cooling/small_cosmo_volume.yml

@@ -30,6 +30,7 @@ Gravity:
 # Parameters of the hydro scheme
 SPH:
   resolution_eta:      1.2348   # "48 Ngb" with the cubic spline kernel
+  h_min_ratio:         0.1
   CFL_condition:       0.1
   initial_temperature: 7075.    # (1 + z_ini)^2 * 2.72K
   minimal_temperature: 100.

examples/ZeldovichPancake_3D/zeldovichPancake.yml

@@ -35,6 +35,7 @@ Statistics:
 SPH:
   resolution_eta:        1.2348   # Target smoothing length in units of the mean inter-particle separation 
   CFL_condition:         0.1      # Courant-Friedrich-Levy condition for time integration.
+  h_min_ratio:           0.1
 
 # Parameters related to the initial conditions
 InitialConditions:

examples/parameter_example.yml

@@ -28,6 +28,7 @@ SPH:
   CFL_condition:         0.1      # Courant-Friedrich-Levy condition for time integration.
   h_tolerance:           1e-4     # (Optional) Relative accuracy of the Netwon-Raphson scheme for the smoothing lengths.
   h_max:                 10.      # (Optional) Maximal allowed smoothing length in internal units. Defaults to FLT_MAX if unspecified.
+  h_min_ratio:           0.       # (Optional) Minimal allowed smoothing length in units of the softening. Defaults to 0 if unspecified.
   max_volume_change:     1.4      # (Optional) Maximal allowed change of kernel volume over one time-step.
   max_ghost_iterations:  30       # (Optional) Maximal number of iterations allowed to converge towards the smoothing length.
   initial_temperature:   0        # (Optional) Initial temperature (in internal units) to set the gas particles at start-up. Value is ignored if set to 0.

src/cell.c

@@ -3642,6 +3642,7 @@ void cell_drift_part(struct cell *c, const struct engine *e, int force) {
   const double dim[3] = {e->s->dim[0], e->s->dim[1], e->s->dim[2]};
   const int with_cosmology = (e->policy & engine_policy_cosmology);
   const float hydro_h_max = e->hydro_properties->h_max;
+  const float hydro_h_min = e->hydro_properties->h_min;
   const integertime_t ti_old_part = c->hydro.ti_old_part;
   const integertime_t ti_current = e->ti_current;
   struct part *const parts = c->hydro.parts;
@@ -3776,6 +3777,7 @@ void cell_drift_part(struct cell *c, const struct engine *e, int force) {
 
       /* Limit h to within the allowed range */
       p->h = min(p->h, hydro_h_max);
+      p->h = max(p->h, hydro_h_min);
 
       /* Compute (square of) motion since last cell construction */
       const float dx2 = xp->x_diff[0] * xp->x_diff[0] +

src/engine.c

@@ -2792,7 +2792,12 @@ void engine_init_particles(struct engine *e, int flag_entropy_ICs,
 
   /* Update the softening lengths */
   if (e->policy & engine_policy_self_gravity)
-    gravity_update(e->gravity_properties, e->cosmology);
+    gravity_props_update(e->gravity_properties, e->cosmology);
+
+  /* Udpate the hydro properties */
+  if (e->policy & engine_policy_hydro)
+    hydro_props_update(e->hydro_properties, e->gravity_properties,
+                       e->cosmology);
 
   /* Start by setting the particles in a good state */
   if (e->nodeID == 0) message("Setting particles to a valid state...");
@@ -3085,7 +3090,12 @@ void engine_step(struct engine *e) {
 
   /* Update the softening lengths */
   if (e->policy & engine_policy_self_gravity)
-    gravity_update(e->gravity_properties, e->cosmology);
+    gravity_props_update(e->gravity_properties, e->cosmology);
+
+  /* Udpate the hydro properties */
+  if (e->policy & engine_policy_hydro)
+    hydro_props_update(e->hydro_properties, e->gravity_properties,
+                       e->cosmology);
 
   /* Trigger a tree-rebuild if we passed the frequency threshold */
   if ((e->policy & engine_policy_self_gravity) &&
@@ -4088,7 +4098,7 @@ void engine_init(struct engine *e, struct space *s, struct swift_params *params,
                  int policy, int verbose, struct repartition *reparttype,
                  const struct unit_system *internal_units,
                  const struct phys_const *physical_constants,
-                 struct cosmology *cosmo, const struct hydro_props *hydro,
+                 struct cosmology *cosmo, struct hydro_props *hydro,
                  const struct entropy_floor_properties *entropy_floor,
                  struct gravity_props *gravity, const struct stars_props *stars,
                  struct pm_mesh *mesh,

src/engine.h

@@ -343,7 +343,7 @@ struct engine {
   struct cosmology *cosmology;
 
   /* Properties of the hydro scheme */
-  const struct hydro_props *hydro_properties;
+  struct hydro_props *hydro_properties;
 
   /* Properties of the entropy floor */
   const struct entropy_floor_properties *entropy_floor;
@@ -419,7 +419,7 @@ void engine_init(struct engine *e, struct space *s, struct swift_params *params,
                  int policy, int verbose, struct repartition *reparttype,
                  const struct unit_system *internal_units,
                  const struct phys_const *physical_constants,
-                 struct cosmology *cosmo, const struct hydro_props *hydro,
+                 struct cosmology *cosmo, struct hydro_props *hydro,
                  const struct entropy_floor_properties *entropy_floor,
                  struct gravity_props *gravity, const struct stars_props *stars,
                  struct pm_mesh *mesh,

src/gravity/Default/gravity.h

@@ -40,7 +40,7 @@ __attribute__((always_inline)) INLINE static float gravity_get_mass(
 }
 
 /**
- * @brief Returns the softening of a particle
+ * @brief Returns the current co-moving softening of a particle
  *
  * @param gp The particle of interest
  * @param grav_props The global gravity properties.

src/gravity/Potential/gravity.h

@@ -39,7 +39,7 @@ __attribute__((always_inline)) INLINE static float gravity_get_mass(
 }
 
 /**
- * @brief Returns the softening of a particle
+ * @brief Returns the current co-moving softening of a particle
  *
  * @param gp The particle of interest
  * @param grav_props The global gravity properties.

src/gravity_properties.c

@@ -99,10 +99,11 @@ void gravity_props_init(struct gravity_props *p, struct swift_params *params,
   }
 
   /* Set the softening to the current time */
-  gravity_update(p, cosmo);
+  gravity_props_update(p, cosmo);
 }
 
-void gravity_update(struct gravity_props *p, const struct cosmology *cosmo) {
+void gravity_props_update(struct gravity_props *p,
+                          const struct cosmology *cosmo) {
 
   /* Current softening lengths */
   double softening;

src/gravity_properties.h

@@ -73,7 +73,7 @@ struct gravity_props {
   /*! Maxium physical softening */
   double epsilon_max_physical;
 
-  /*! Current sftening length */
+  /*! Current softening length */
   float epsilon_cur;
 
   /*! Square of current softening length */
@@ -90,7 +90,8 @@ void gravity_props_print(const struct gravity_props *p);
 void gravity_props_init(struct gravity_props *p, struct swift_params *params,
                         const struct cosmology *cosmo, int with_cosmology,
                         int periodic);
-void gravity_update(struct gravity_props *p, const struct cosmology *cosmo);
+void gravity_props_update(struct gravity_props *p,
+                          const struct cosmology *cosmo);
 
 #if defined(HAVE_HDF5)
 void gravity_props_print_snapshot(hid_t h_grpsph,