Initialization

This page describes the initialization phase of the Shallow-Water example implementation.

Overview

The initialization phase prepares all data structures and parameters before the main computation loop.

Main Steps

1. Library Initialization

! Initialize Tolosa-lib
call tolosa_init()

! Initialize MPI if parallel
call mpi_init_tolosa()

2. Mesh Loading

Load the computational mesh:

type(msh) :: mesh

! Load mesh from file
call mesh%load('mesh.msh')

! Generate connectivity
call mesh%build_connectivity()

! Partition for MPI
call mesh%partition(num_procs)

3. Field Allocation

Allocate arrays for physical variables:

! Water depth
real(rp), allocatable :: h(:)

! Velocities
real(rp), allocatable :: u(:), v(:)

! Allocate at cell centers
allocate(h(mesh%nc))
allocate(u(mesh%nc))
allocate(v(mesh%nc))

4. Initial Conditions

Set initial values:

! Constant depth
h(:) = 10.0_rp

! At rest
u(:) = 0.0_rp
v(:) = 0.0_rp

! Or call user function
call set_initial_conditions(mesh, h, u, v)

5. Boundary Conditions

Define boundary types:

! Wall boundaries
mesh%bc_type(1:10) = BC_WALL

! Open boundaries
mesh%bc_type(11:20) = BC_OPEN

! Periodic boundaries
mesh%bc_type(21:30) = BC_PERIODIC

6. Parameters Setup

Set numerical and physical parameters:

! Physical parameters
real(rp) :: g = 9.81_rp     ! Gravity
real(rp) :: manning = 0.03_rp ! Manning coefficient

! Numerical parameters
real(rp) :: cfl = 0.5_rp    ! CFL number
integer :: scheme = SCHEME_HLL

! Time parameters
real(rp) :: dt              ! Time step
real(rp) :: t_end = 100.0_rp ! End time

7. Output Initialization

Setup output files:

type(VTK_file) :: vtk_output
type(csv_file) :: csv_output

! Initialize VTK output
call vtk_output%init('results/output', mesh)

! Initialize CSV for time series
call csv_output%init('results/gauges.csv')

8. Timers Setup

Initialize performance timers:

type(timer) :: t_flux, t_update, t_output

call t_flux%init('Flux computation')
call t_update%init('Field update')
call t_output%init('Output writing')

Complete Initialization Routine

subroutine initialize_simulation()
  use mod_tolosa
  implicit none

  ! Initialize library
  call tolosa_init()

  ! Load mesh
  call mesh%load(mesh_file)
  call mesh%build_connectivity()

  ! Allocate fields
  allocate(h(mesh%nc))
  allocate(u(mesh%nc))
  allocate(v(mesh%nc))

  ! Set initial conditions
  call set_initial_conditions()

  ! Setup boundaries
  call setup_boundaries()

  ! Initialize outputs
  call init_outputs()

  ! Initialize timers
  call init_timers()

  if (rank == 0) then
    print *, 'Initialization complete'
    print *, 'Number of cells:', mesh%nc
    print *, 'Number of processors:', num_procs
  end if

end subroutine initialize_simulation

Memory Considerations

For large meshes, memory usage is approximately:

where:

• is the number of cells
• is the average number of edges per cell
• 3 fields (h, u, v) × 8 bytes (real64)

Error Checking

Always check for errors:

integer :: ierr

call mesh%load(mesh_file, ierr)
if (ierr /= 0) then
  print *, 'Error loading mesh'
  call tolosa_abort()
end if

Next Steps

• Computation Loop - Main time-stepping algorithm
• Finalization - Cleanup and final output