diff --git a/doc/RTD/source/ParameterFiles/parameter_description.rst b/doc/RTD/source/ParameterFiles/parameter_description.rst
index f29d5a6b47b3ad5e0e3bf9f1575eed254718ae37..45b68c9e9c490df52de675ba3d37011d4b48222b 100644
--- a/doc/RTD/source/ParameterFiles/parameter_description.rst
+++ b/doc/RTD/source/ParameterFiles/parameter_description.rst
@@ -601,9 +601,13 @@ the start and end times or scale factors from the parameter file.
* Dimensionless pre-factor of the maximal allowed displacement:
``max_dt_RMS_factor`` (default: ``0.25``)
-
-This value rarely needs altering. See the theory documents for its
-precise meaning.
+* Whether or not only the gas particle masses should be considered for
+ the baryon component of the calculation: ``dt_RMS_use_gas_only`` (default: ``0``)
+
+These values rarely need altering. The second parameter is only
+meaningful if a subgrid model produces star (or other) particles with
+masses substantially smaller than the gas masses. See the theory
+documents for the precise meanings.
A full time-step section for a non-cosmological run would be:
@@ -620,10 +624,11 @@ Whilst for a cosmological run, one would need:
.. code:: YAML
TimeIntegration:
- dt_max: 1e-4
- dt_min: 1e-10
- max_dt_RMS_factor: 0.25 # Default optional value
-
+ dt_max: 1e-4
+ dt_min: 1e-10
+ max_dt_RMS_factor: 0.25 # Default optional value
+ dt_RMS_use_gas_only: 0 # Default optional value
+
.. _Parameters_ICs:
Initial Conditions
diff --git a/examples/GEAR/AgoraCosmo/agora_cosmo.yml b/examples/GEAR/AgoraCosmo/agora_cosmo.yml
index 74b4d855b5ad5c9fedfefbb38bcfbdbfd4608046..b4c4b6b9dac625f835e2baca017d1e3f07bec5f5 100644
--- a/examples/GEAR/AgoraCosmo/agora_cosmo.yml
+++ b/examples/GEAR/AgoraCosmo/agora_cosmo.yml
@@ -14,6 +14,7 @@ TimeIntegration:
dt_min: 1e-16 # The minimal time-step size of the simulation (in internal units).
dt_max: 0.1 # The maximal time-step size of the simulation (in internal units).
max_dt_RMS_factor: 0.25 # (Optional) Dimensionless factor for the maximal displacement allowed based on the RMS velocities.
+ dt_RMS_use_gas_only: 1
# Cosmological parameters
Cosmology:
diff --git a/examples/GEAR/ZoomIn/zoom_in.yml b/examples/GEAR/ZoomIn/zoom_in.yml
index feb87d67b6c46b74b084a787784c0ce17bc18e62..9e9135d04deecd15632517b123e24915a5ccfad5 100644
--- a/examples/GEAR/ZoomIn/zoom_in.yml
+++ b/examples/GEAR/ZoomIn/zoom_in.yml
@@ -19,7 +19,8 @@ TimeIntegration:
dt_min: 1e-16 # The minimal time-step size of the simulation (in internal units).
dt_max: 0.1 # The maximal time-step size of the simulation (in internal units).
max_dt_RMS_factor: 0.25 # (Optional) Dimensionless factor for the maximal displacement allowed based on the RMS velocities.
-
+ dt_RMS_use_gas_only: 1
+
# Cosmological parameters
Cosmology:
h: 0.673 # Reduced Hubble constant
diff --git a/examples/parameter_example.yml b/examples/parameter_example.yml
index 8239c4c44b820220d511e828551ef72e2f3ce214..bbc0807bbf19af836e0247ed957509448ecaebef 100644
--- a/examples/parameter_example.yml
+++ b/examples/parameter_example.yml
@@ -143,12 +143,13 @@ Scheduler:
# Parameters governing the time integration (Set dt_min and dt_max to the same value for a fixed time-step run.)
TimeIntegration:
- time_begin: 0. # The starting time of the simulation (in internal units).
- time_end: 1. # The end time of the simulation (in internal units).
- dt_min: 1e-6 # The minimal time-step size of the simulation (in internal units).
- dt_max: 1e-2 # The maximal time-step size of the simulation (in internal units).
- max_dt_RMS_factor: 0.25 # (Optional) Dimensionless factor for the maximal displacement allowed based on the RMS velocities.
-
+ time_begin: 0. # The starting time of the simulation (in internal units).
+ time_end: 1. # The end time of the simulation (in internal units).
+ dt_min: 1e-6 # The minimal time-step size of the simulation (in internal units).
+ dt_max: 1e-2 # The maximal time-step size of the simulation (in internal units).
+ max_dt_RMS_factor: 0.25 # (Optional) Dimensionless factor for the maximal displacement allowed based on the RMS velocities.
+ dt_RMS_use_gas_only: 0 # (Optional) When computing the max RMS dt, should only the gas particles be considered in the baryon component calculation?
+
# Parameters governing the snapshots
Snapshots:
basename: output # Common part of the name of output files.
diff --git a/src/engine.c b/src/engine.c
index ef2857c5d0706b70cc79bcf3c87fe8cfa60d4e0e..c09a55eb32d06ea8a70e3441746014dffba19187 100644
--- a/src/engine.c
+++ b/src/engine.c
@@ -2820,6 +2820,8 @@ void engine_init(
e->dt_max_RMS_displacement = FLT_MAX;
e->max_RMS_displacement_factor = parser_get_opt_param_double(
params, "TimeIntegration:max_dt_RMS_factor", 0.25);
+ e->max_RMS_dt_use_only_gas = parser_get_opt_param_int(
+ params, "TimeIntegration:dt_RMS_use_gas_only", 0);
e->dt_kick_grav_mesh_for_io = 0.f;
e->a_first_statistics =
parser_get_opt_param_double(params, "Statistics:scale_factor_first", 0.1);
@@ -3115,9 +3117,12 @@ void engine_recompute_displacement_constraint(struct engine *e) {
/* Baryon case */
if (N_b > 0.f) {
- /* Minimal mass for the baryons */
- const float min_mass_b =
- min4(min_mass[0], min_mass[3], min_mass[4], min_mass[5]);
+ /* Minimal mass for the bayons */
+ float min_mass_b;
+ if (e->max_RMS_dt_use_only_gas)
+ min_mass_b = min_mass[0];
+ else
+ min_mass_b = min4(min_mass[0], min_mass[3], min_mass[4], min_mass[5]);
/* Inter-particle sepration for the baryons */
const float d_b = cbrtf(min_mass_b / (Ob * rho_crit0));
diff --git a/src/engine.h b/src/engine.h
index 248df75026519061f7e5f2944448d152eeddb809..e83c21f1928d7cbef540cb2d6220b559ade4e165 100644
--- a/src/engine.h
+++ b/src/engine.h
@@ -163,6 +163,10 @@ struct engine {
/* Dimensionless factor for the RMS time-step condition. */
double max_RMS_displacement_factor;
+ /* When computing the max RMS dt, should only the gas particles
+ * be considered as the baryon component? */
+ int max_RMS_dt_use_only_gas;
+
/* Time of the simulation beginning */
double time_begin;