m_dt.f90

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!> Module to set the time step
module m_dt
  use m_af_all
  use m_types
 
  implicit none
  private
 
  ! Number of time step restrictions
  integer, parameter, public :: dt_num_cond = 4
 
  ! Array of time step restrictions per thread
  real(dp), public :: dt_limits(dt_num_cond)
 
  ! Index of CFL condition
  integer, parameter, public :: dt_ix_cfl = 1
 
  ! Index of dielectric relaxation time step condition
  integer, parameter, public :: dt_ix_drt = 2
 
  ! Index of reaction rate time step condition
  integer, parameter, public :: dt_ix_rates = 3
 
  ! Index of other time step restrictions
  integer, parameter, public :: dt_ix_other = 4
 
  ! Safety factor for the time step
  real(dp), public, protected :: dt_safety_factor = 0.9_dp
 
  !> CFL number to use
  real(dp), public, protected :: dt_cfl_number = undefined_real
 
  !> If > 0, a density to control the accuracy of the chemistry time step
  real(dp), public, protected :: dt_chemistry_nmin = -1.0_dp
 
  !> Limit dt to prevent negative densities due to loss reactions
  logical, public, protected :: dt_chemistry_limit_loss = .true.
 
  ! Maximum allowed time step
  real(dp), public, protected :: dt_max = 1.0e-11_dp
 
  ! Minimum allowed time step
  real(dp), public, protected :: dt_min = 1.0e-14_dp
 
  !> Maximal relative increase dt for the next iteration
  real(dp), public, protected :: dt_max_growth_factor = 2.0_dp
 
  !> Which time integrator is used
  integer, public, protected :: time_integrator
 
  public :: dt_initialize
 
contains
 
  !> Initialize the time step module
  subroutine dt_initialize(cfg)
    use m_config
    type(cfg_t), intent(inout) :: cfg
    real(dp)                   :: default_cfl_number = 0.5_dp
    character(len=name_len)    :: integrator
 
    !> [relevant_parameters]
    call cfg_add_get(cfg, "dt_max", dt_max, &
         "The maximum timestep (s)")
    call cfg_add_get(cfg, "dt_min", dt_min, &
         "The minimum timestep (s)")
    call cfg_add_get(cfg, "dt_safety_factor", dt_safety_factor, &
         "Safety factor for the time step")
    call cfg_add_get(cfg, "dt_cfl_number", dt_cfl_number, &
         "CFL number to use")
    call cfg_add_get(cfg, "dt_chemistry_nmin", dt_chemistry_nmin, &
         "If > 0, a density to control the accuracy of the chemistry time step")
    call cfg_add_get(cfg, "dt_chemistry_limit_loss", dt_chemistry_limit_loss, &
         "Limit dt to prevent negative densities due to loss reactions")
    !> [relevant_parameters]
 
    call cfg_add_get(cfg, "dt_max_growth_factor", dt_max_growth_factor, &
         "Maximal relative increase dt for the next iteration")
 
    integrator = "heuns_method"
    call cfg_add_get(cfg, "time_integrator", integrator, &
         "Time integrator (use arbitrary value to see options)")
 
    do time_integrator = 1, af_num_integrators
       if (integrator == af_integrator_names(time_integrator)) exit
    end do
 
    if (time_integrator == af_num_integrators+1) then
       print *, "Use one of the following time integrators:"
       do time_integrator = 1, af_num_integrators
          print *, trim(af_integrator_names(time_integrator))
       end do
       error stop "Unknown time integrator"
    end if
 
    ! Set CFL number automatically if not set
    if (dt_cfl_number <= undefined_real) dt_cfl_number = default_cfl_number
 
  end subroutine dt_initialize
 
end module m_dt