!> Module for physical and numeric constants
module mod_constants

  implicit none
  public

  ! A very small real number (but above machine precision)
  double precision, parameter :: smalldouble = 1.D-12

  !> A very large real number
  double precision, parameter :: bigdouble = 1.D+99

  !> A very large integer
  integer, parameter :: biginteger = 10000000

  !> some frequently used numbers
  double precision, parameter :: zero    = 0.0d0
  double precision, parameter :: one     = 1.0d0
  double precision, parameter :: two     = 2.0d0
  double precision, parameter :: half    = 0.5d0
  double precision, parameter :: quarter = 0.25d0
  double precision, parameter :: third   = 1.d0/3.0d0

  !> Pi
  double precision, parameter ::&
      dpi=3.141592653589793238462643383279502884197169399375105d0

  !> Proton mass in cgs
  double precision, parameter :: mp_cgs = 1.672621777d-24 ! g

  !> Hydrogen mass in cgs
  double precision, parameter :: mH_cgs = 1.6733D-24 ! g

  !> Boltzmann constant in cgs
  double precision, parameter :: kB_cgs = 1.3806488d-16 ! erg K-1,K-1,K-1

  !> Proton mass in SI
  double precision, parameter :: mp_SI = 1.672621777d-27 ! kg

  !> Boltzmann constant in SI
  double precision, parameter :: kB_SI = 1.3806488d-23 ! J K-1,K-1,K-1

  !> Permeability in SI
  double precision, parameter :: miu0_SI = 1.2566370614d-6 ! H m-1,m-1,m-1

  !> Speed of light in SI
  double precision, parameter :: c_SI = 2.99792458d8 ! m s-1,s-1,s-1

  double precision, PARAMETER :: const_c     = 2.99792458d10 !cm s-1,s-1,s-1           ; Speed of light
  double precision, PARAMETER :: const_me    = 9.1093897d-28 !g                 ; Electron mass
  double precision, PARAMETER :: const_mp    = 1.672621777d-24 !g                 ; Proton mass
  double precision, PARAMETER :: const_e     = 4.8032068d-10 !g1/2,g1/2,g1/2 cm3/2,cm3/2,cm3/2 s-1,s-1,s-1 ; Electron charge
  double precision, PARAMETER :: const_LSun  = 3.828d33 !erg s-1,s-1,s-1          ; Solar luminosity
  double precision, PARAMETER :: const_MSun  = 1.98892d33 !g                 ; Solar mass
  double precision, PARAMETER :: const_RSun  = 6.9570d10 !cm                ; Solar radius
  double precision, PARAMETER :: const_kB    = 1.3806488d-16 !erg K-1,K-1,K-1          ; Boltzmann constant
  double precision, PARAMETER :: const_h     = 6.6260755d-27 !erg s             ; Planck constant
  double precision, parameter :: const_pc    = 3.08567758128d18 !cm                ; 1 parsec

  double precision, PARAMETER :: const_sigma  = 5.670367d-5 !erg cm-2,cm-2,cm-2 K-4,K-4,K-4 s-1,s-1,s-1 ; Stefan-Boltzman constant
  double precision, PARAMETER :: const_G      = 6.67191d-8 !cm3,cm3,cm3 g-1,g-1,g-1 s-2,s-2,s-2      ; Cavendish gravitational constant
  double precision, PARAMETER :: const_rad_a  = 7.5657e-15 !erg cm-3,cm-3,cm-3 K-4,K-4,K-4      ; radiation density constant
  double precision, PARAMETER :: const_kappae = 0.34d0 !cm2,cm2,cm2 g-1,g-1,g-1           ; free-electron scattering opacity

  ! Conversion factors:
  double precision, PARAMETER :: const_eV    = 1.6021772d-12 !erg/eV            ; Electron volt
  double precision, PARAMETER :: const_Tera  = 1.d12 !-                 ; Tera
  double precision, PARAMETER :: const_Peta  = 1.d15 !-                 ; Peta
  double precision, PARAMETER :: const_years = 3.1536d7 !s year-1,year-1,year-1         ; seconds in a year

end module mod_constants