Only read the DM softenings if we have DM particles. Same fr baryons.

examples/main.c

@@ -951,6 +951,11 @@ int main(int argc, char *argv[]) {
           N_total[swift_type_black_hole], N_total[swift_type_dark_matter],
           N_total[swift_type_dark_matter_background]);
 
+    const int with_DM_particles = N_total[swift_type_dark_matter] > 0;
+    const int with_baryon_particles =
+        (N_total[swift_type_gas] + N_total[swift_type_stars] +
+         N_total[swift_type_black_hole]) > 0;
+
     /* Do we have background DM particles? */
     const int with_DM_background_particles =
         N_total[swift_type_dark_matter_background] > 0;
@@ -976,7 +981,8 @@ int main(int argc, char *argv[]) {
     bzero(&gravity_properties, sizeof(struct gravity_props));
     if (with_self_gravity)
       gravity_props_init(&gravity_properties, params, &prog_const, &cosmo,
-                         with_cosmology, with_DM_background_particles,
+                         with_cosmology, with_baryon_particles,
+                         with_DM_particles, with_DM_background_particles,
                          periodic);
 
     /* Initialise the external potential properties */

examples/main_fof.c

@@ -497,6 +497,11 @@ int main(int argc, char *argv[]) {
         N_total[swift_type_black_hole], N_total[swift_type_dark_matter],
         N_total[swift_type_dark_matter_background]);
 
+  const int with_DM_particles = N_total[swift_type_dark_matter] > 0;
+  const int with_baryon_particles =
+      (N_total[swift_type_gas] + N_total[swift_type_stars] +
+       N_total[swift_type_black_hole]) > 0;
+
   /* Do we have background DM particles? */
   const int with_DM_background_particles =
       N_total[swift_type_dark_matter_background] > 0;
@@ -519,8 +524,8 @@ int main(int argc, char *argv[]) {
   /* Initialise the gravity scheme */
   bzero(&gravity_properties, sizeof(struct gravity_props));
   gravity_props_init(&gravity_properties, params, &prog_const, &cosmo,
-                     /*with_cosmology=*/1, with_DM_background_particles,
-                     periodic);
+                     /*with_cosmology=*/1, with_baryon_particles,
+                     with_DM_particles, with_DM_background_particles, periodic);
 
   /* Initialise the long-range gravity mesh */
   if (periodic) {

src/gravity_properties.c

@@ -41,6 +41,7 @@
 void gravity_props_init(struct gravity_props *p, struct swift_params *params,
                         const struct phys_const *phys_const,
                         const struct cosmology *cosmo, const int with_cosmology,
+                        const int has_baryons, const int has_DM,
                         const int is_zoom_simulation, const int periodic) {
 
   /* Tree updates */
@@ -90,17 +91,25 @@ void gravity_props_init(struct gravity_props *p, struct swift_params *params,
   /* Softening parameters */
   if (with_cosmology) {
 
-    /* Maximal physical softening taken straight from the parameter file */
-    p->epsilon_DM_max_physical =
-        parser_get_param_double(params, "Gravity:max_physical_DM_softening");
-    p->epsilon_baryon_max_physical = parser_get_param_double(
-        params, "Gravity:max_physical_baryon_softening");
+    if (has_DM) {
+      /* Maximal physical softening taken straight from the parameter file */
+      p->epsilon_DM_max_physical =
+          parser_get_param_double(params, "Gravity:max_physical_DM_softening");
 
-    /* Co-moving softenings taken straight from the parameter file */
-    p->epsilon_DM_comoving =
-        parser_get_param_double(params, "Gravity:comoving_DM_softening");
-    p->epsilon_baryon_comoving =
-        parser_get_param_double(params, "Gravity:comoving_baryon_softening");
+      /* Co-moving softenings taken straight from the parameter file */
+      p->epsilon_DM_comoving =
+          parser_get_param_double(params, "Gravity:comoving_DM_softening");
+    }
+
+    if (has_baryons) {
+      /* Maximal physical softening taken straight from the parameter file */
+      p->epsilon_baryon_max_physical = parser_get_param_double(
+          params, "Gravity:max_physical_baryon_softening");
+
+      /* Co-moving softenings taken straight from the parameter file */
+      p->epsilon_baryon_comoving =
+          parser_get_param_double(params, "Gravity:comoving_baryon_softening");
+    }
 
     if (is_zoom_simulation) {
 
@@ -122,10 +131,14 @@ void gravity_props_init(struct gravity_props *p, struct swift_params *params,
 
   } else {
 
-    p->epsilon_DM_max_physical =
-        parser_get_param_double(params, "Gravity:max_physical_DM_softening");
-    p->epsilon_baryon_max_physical = parser_get_param_double(
-        params, "Gravity:max_physical_baryon_softening");
+    if (has_DM) {
+      p->epsilon_DM_max_physical =
+          parser_get_param_double(params, "Gravity:max_physical_DM_softening");
+    }
+    if (has_baryons) {
+      p->epsilon_baryon_max_physical = parser_get_param_double(
+          params, "Gravity:max_physical_baryon_softening");
+    }
 
     p->epsilon_DM_comoving = p->epsilon_DM_max_physical;
     p->epsilon_baryon_comoving = p->epsilon_baryon_max_physical;

src/gravity_properties.h

@@ -120,6 +120,7 @@ void gravity_props_print(const struct gravity_props *p);
 void gravity_props_init(struct gravity_props *p, struct swift_params *params,
                         const struct phys_const *phys_const,
                         const struct cosmology *cosmo, const int with_cosmology,
+                        const int has_baryons, const int has_DM,
                         const int is_zoom_simulation, const int periodic);
 void gravity_props_update(struct gravity_props *p,
                           const struct cosmology *cosmo);