module globals
  implicit none

  include "mpif.h"

  integer, parameter :: Grid_size = 80
  real (8), parameter :: errorstop = 1e-4
  real (8), parameter :: sorfracfinal = 1.8
  integer, parameter :: maxiter = 10000
  character (13), parameter :: design_file = 'sample_design'

  ! material types for storing the heat sink design in `heatsink_design'
  byte, parameter :: Aluminium = 1
  byte, parameter :: Aluminium_touching_cpu = 2
  byte, parameter :: Air = 3

  ! physical parameters (SI units)
  real (8), parameter :: Domain_size = 0.04 ! (4 cm)^3 region
  real (8), parameter :: Chip_size = 0.02 ! (2 cm)^2 chip
  real (8), parameter :: Delta = Domain_size / real (Grid_size)
  real (8), parameter :: CPU_watts = 50.0

  ! physical constants
  real (8), parameter :: k_al = 235.0 ! thermal conductivity of aluminium
  real (8), parameter :: k_air = 0.026 ! thermal conductivity of air
  real (8), parameter :: C_cpu = CPU_watts / (Chip_size**2) / k_al ! temperature gradient at CPU boundary
  real (8), parameter :: C_al_factor = k_air / k_al / 0.0001 ! for temperature difference at air boundary
  real (8), parameter :: Celsius_offset = 273.15
  real (8), parameter :: Air_temp_C = 25.0
  real (8), parameter :: Air_temp_K = Celsius_offset + Air_temp_C
  real (8), parameter :: onesixth = 1.0 / 6.0
  
  ! array describing the structure of the heatsink
  byte, dimension (:, :, :), allocatable :: heatsink_design
  real (8), dimension (:, :, :), allocatable :: temp3d

  ! MPI values
  integer :: mpi_cpu_count, mpi_cpu_id
  integer :: mpi_error_code
  integer, dimension(MPI_STATUS_SIZE) :: mpistatus
end module globals