decomp_init Subroutine

public subroutine decomp_init(d, nx_global, ny_global, px, py, rank)

Initialise decomposition for a given rank

Distributes remainder cells to the first ranks in each direction. rank is mapped to (rx, ry) using row-major order: rank = ry * px + rx

Arguments

Type IntentOptional Attributes Name
type(decomp_t), intent(out) :: d

Decomposition descriptor to populate
integer, intent(in) :: nx_global

Total physical cells in x
integer, intent(in) :: ny_global

Total physical cells in y
integer, intent(in) :: px

Process grid size in x
integer, intent(in) :: py

Process grid size in y
integer, intent(in) :: rank

MPI rank (0-based)

Called by

proc~~decomp_init~~CalledByGraph proc~decomp_init decomp_init proc~decomp_init_from_config decomp_init_from_config proc~decomp_init_from_config->proc~decomp_init proc~engine_setup engine_setup proc~engine_setup->proc~decomp_init_from_config proc~complete_ocean_create complete_ocean_create proc~complete_ocean_create->proc~engine_setup proc~driver_run_ocean driver_run_ocean proc~driver_run_ocean->proc~engine_setup proc~driver_validate driver_validate proc~driver_validate->proc~engine_setup proc~driver_run driver_run proc~driver_run->proc~driver_run_ocean proc~rdb_ocean_create_finalize rdb_ocean_create_finalize proc~rdb_ocean_create_finalize->proc~complete_ocean_create proc~rdb_ocean_create_from_string rdb_ocean_create_from_string proc~rdb_ocean_create_from_string->proc~complete_ocean_create

Variables

Type Visibility Attributes Name Initial
integer, private :: base_nx
integer, private :: base_ny
integer, private :: rem_nx
integer, private :: rem_ny

Source Code

   subroutine decomp_init(d, nx_global, ny_global, px, py, rank)
      !! Initialise decomposition for a given rank
      !!
      !! Distributes remainder cells to the first ranks in each direction.
      !! rank is mapped to (rx, ry) using row-major order: rank = ry * px + rx
      type(decomp_t), intent(out) :: d
         !! Decomposition descriptor to populate
      integer, intent(in) :: nx_global
         !! Total physical cells in x
      integer, intent(in) :: ny_global
         !! Total physical cells in y
      integer, intent(in) :: px
         !! Process grid size in x
      integer, intent(in) :: py
         !! Process grid size in y
      integer, intent(in) :: rank
         !! MPI rank (0-based)

      integer :: base_nx, rem_nx, base_ny, rem_ny

      d%px = px
      d%py = py
      d%nx_global = nx_global
      d%ny_global = ny_global

      ! Row-major mapping: rank = ry * px + rx
      d%rx = mod(rank, px)
      d%ry = rank/px

      ! Distribute cells with remainder going to first ranks
      base_nx = nx_global/px
      rem_nx = mod(nx_global, px)
      if (d%rx < rem_nx) then
         d%nx_local = base_nx + 1
         d%i_start = d%rx*(base_nx + 1) + 1
      else
         d%nx_local = base_nx
         d%i_start = rem_nx*(base_nx + 1) + (d%rx - rem_nx)*base_nx + 1
      end if

      base_ny = ny_global/py
      rem_ny = mod(ny_global, py)
      if (d%ry < rem_ny) then
         d%ny_local = base_ny + 1
         d%j_start = d%ry*(base_ny + 1) + 1
      else
         d%ny_local = base_ny
         d%j_start = rem_ny*(base_ny + 1) + (d%ry - rem_ny)*base_ny + 1
      end if

      ! Boundary flags
      d%has_west = (d%rx == 0)
      d%has_east = (d%rx == px - 1)
      d%has_south = (d%ry == 0)
      d%has_north = (d%ry == py - 1)

   end subroutine decomp_init