General

This section in the config.yaml file contains all general/global configuration options to SMASH.

Available Settings

End_Time (double, required):
The time in fm after which the evolution is stopped. Note that the starting time depends on the chosen Modus.

Randomseed (int, required):
Initial seed for the random number generator. If this is negative, the seed will be randomly generated by the operating system.

Nevents (int, required):
Number of events to calculate.

Use_Grid (bool, optional, default = true):

• true - A grid is used to reduce the combinatorics of interaction lookup
  
• false - No grid is used.

Time_Step_Mode (string, optional, default = Fixed):
The mode of time stepping. Possible values:

• None - No time steps and no collision-finding grid are used. Cannot be used with potentials.
  
• Fixed - Fixed-sized time steps at which collision-finding grid is used. More efficient for systems with many particles.
  Metric_Type (string, optional, default = NoExpansion):
  Select which kind of expansion the metric should have. This needs only be specified for the sphere modus:
• NoExpansion - Default SMASH run, with Minkowski metric
  
• MasslessFRW - FRW expansion going as t^(1/2)
• MassiveFRW - FRW expansion going as t^(2/3)
• Exponential - FRW expansion going as e^(t/2)

Expansion_Rate (double, optional, default = 0.1):
Corresponds to the speed of expansion of the universe in non minkowski metrics if MetricType is any other than NoExpansion.
It corresponds to \(b_r/l_0\) if the metric type is MasslessFRW or MassiveFRW, and to the parameter b in the Exponential expansion where \(a(t) ~ e^{bt/2}\).

Example: Configuring General Properties

The following example provides a possibility for the General configuration.

General:
    Modus: Collider
    Delta_Time: 0.1
    Testparticles: 1
    Gaussian_Sigma: 1.0
    Gauss_Cutoff_In_Sigma: 3.0
    End_Time: 100.0
    Randomseed: -1
    Nevents: 20
    Use_Grid: True
    Time_Step_Mode: Fixed

In the case of an expanding sphere setup, change the Modus and provide further information about the expansion.

    Modus: Sphere
    MetricType: MasslessFRW
    Expansion_Rate: 0.1

Modus (string, required):
Selects a modus for the calculation, e.g. infinite matter calculation, collision of two particles or collision of nuclei. The modus will be configured in Modi. Recognized values are:

• Collider - For collisions of nuclei or compound objects. See smash::ColliderModus
• Sphere - For calculations of the expansion of a thermalized sphere. See smash::SphereModus
• Box - For infinite matter calculation in a rectangular box. See smash::BoxModus
• List - For given external particle list. See smash::ListModus

Delta_Time (double, optional, default: 1.0):
Time step for the calculation, in fm/c. Not required for timestepless mode.

Testparticles (int, optional, default = 1):
How many test particles per real particle should be simulated.

Gaussian_Sigma (double, optional, default = 1.0):
Width of gaussians that represent Wigner density of particles, in fm.

Gauss_Cutoff_In_Sigma (double, optional, default = 4.0):
Distance in sigma at which gaussian is considered 0.