added timestep multiplier as extra parameter

examples/IsothermalPotential/GravityOnly/externalGravity.yml

@@ -63,11 +63,12 @@ PointMass:
 	position_y:      50.
 	position_z:      50.	
 	mass:            1e10     # mass of external point mass in internal units
+	timestep_mult:   0.03     # controls time step
 
 IsothermalPotential:
-	position_x:      100.     # location of external point mass in internal units
+	position_x:      100.     # location of centre of isothermal potential in internal units
 	position_y:      100.
 	position_z:      100.	
 	vrot:            200.     # rotation speed of isothermal potential in internal units
-
+	timestep_mult:   0.03     # controls time step
 

src/potentials.c

@@ -46,6 +46,8 @@ void potential_init(const struct swift_params* parameter_file,
       parser_get_param_double(parameter_file, "PointMass:position_z");
   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");
 
 #endif /* EXTERNAL_POTENTIAL_POINTMASS */
 #ifdef EXTERNAL_POTENTIAL_ISOTHERMALPOTENTIAL
@@ -57,6 +59,8 @@ 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(parameter_file, "IsothermalPotential:timestep_mult");
 #endif /* EXTERNAL_POTENTIAL_ISOTHERMALPOTENTIAL */
 }
 
@@ -68,13 +72,15 @@ void potential_init(const struct swift_params* parameter_file,
 void potential_print(const struct external_potential* potential) {
 
 #ifdef EXTERNAL_POTENTIAL_POINTMASS
-  message("Point mass properties are (x,y,z) = (%e, %e, %e), M = %e",
+  message("Point mass properties are (x,y,z) = (%e, %e, %e), M = %e timestep multiplier = %e",
           potential->point_mass.x, potential->point_mass.y,
-          potential->point_mass.z, potential->point_mass.mass);
+          potential->point_mass.z, potential->point_mass.mass,
+			 potential->point_mass.timestep_mult);
 #endif /* EXTERNAL_POTENTIAL_POINTMASS */
 #ifdef EXTERNAL_POTENTIAL_ISOTHERMALPOTENTIAL
-  message("Isothermal potential properties are (x,y,z) = (%e, %e, %e), vrot = %e",
+  message("Isothermal potential properties are (x,y,z) = (%e, %e, %e), vrot = %e timestep multiplier= %e",
 			 potential->isothermal_potential.x, potential->isothermal_potential.y,
-  			 potential->isothermal_potential.z, potential->isothermal_potential.vrot);
+  			 potential->isothermal_potential.z, potential->isothermal_potential.vrot,
+			 potential->isothermal_potential.timestep_mult);
 #endif /* EXTERNAL_POTENTIAL_ISOTHERMALPOTENTIAL */
 }

src/potentials.h

@@ -42,12 +42,14 @@ struct external_potential {
   struct {
     double x, y, z;
     double mass;
+	 double timestep_mult;
   } point_mass;
 #endif
 #ifdef EXTERNAL_POTENTIAL_ISOTHERMALPOTENTIAL
   struct {
 	 double x, y, z;
 	 double vrot;
+	 double timestep_mult;
   } isothermal_potential;
 #endif
 };
@@ -83,7 +85,8 @@ __attribute__((always_inline))
 
   //  error(" dx= %e dvx= %e rinv2= %e a2= %e dota_2= %e dt= %e", dx, g->v_full[1], rinv2, a_2, dota_2, 0.03f * sqrtf(a_2 / dota_2));
 
-  return EXTERNAL_GRAVITY_TIMESTEP_PREFACTOR * sqrtf(a_2 / dota_2);
+  //return EXTERNAL_GRAVITY_TIMESTEP_PREFACTOR * sqrtf(a_2 / dota_2);
+  return potential->isothermal_potential.timestep_mult * sqrtf(a_2 / dota_2);
 }
 /**
  * @brief Computes the gravitational acceleration of a particle due to a point
@@ -142,7 +145,8 @@ external_gravity_pointmass_timestep(const struct external_potential* potential,
   const float a_2 = g->a_grav[0] * g->a_grav[0] + g->a_grav[1] * g->a_grav[1] +
                     g->a_grav[2] * g->a_grav[2];
 
-  return EXTERNAL_GRAVITY_TIMESTEP_PREFACTOR * sqrtf(a_2 / dota_2);
+  /*  return EXTERNAL_GRAVITY_TIMESTEP_PREFACTOR * sqrtf(a_2 / dota_2); */
+  return potential->point_mass.timestep_mult * sqrtf(a_2 / dota_2);
 }
 
 /**