1: module ex13f90auxmodule
  2:   implicit none
  3: contains
  4:   !
  5:   ! A subroutine which returns the boundary conditions.
  6:   !
  7:   subroutine get_boundary_cond(b_x,b_y,b_z)
  8: #include <petsc/finclude/petscdm.h>
  9:     use petscdm
 10:     DMBoundaryType,intent(inout) :: b_x,b_y,b_z

 12:     ! Here you may set the BC types you want
 13:     b_x = DM_BOUNDARY_GHOSTED
 14:     b_y = DM_BOUNDARY_GHOSTED
 15:     b_z = DM_BOUNDARY_GHOSTED

 17:   end subroutine get_boundary_cond
 18:   !
 19:   ! A function which returns the RHS of the equation we are solving
 20:   !
 21:   function dfdt_vdp(t,dt,ib1,ibn,jb1,jbn,kb1,kbn,imax,jmax,kmax,n,f)
 22:     !
 23:     ! Right-hand side for the van der Pol oscillator.  Very simple system of two
 24:     ! ODEs.  See Iserles, eq (5.2).
 25:     !
 26:     PetscReal, intent(in) :: t,dt
 27:     PetscInt, intent(in) :: ib1,ibn,jb1,jbn,kb1,kbn,imax,jmax,kmax,n
 28:     PetscReal, dimension(n,ib1:ibn,jb1:jbn,kb1:kbn), intent(inout) :: f
 29:     PetscReal, dimension(n,imax,jmax,kmax) :: dfdt_vdp
 30:     PetscReal, parameter :: mu=1.4, one=1.0
 31:     !
 32:     dfdt_vdp(1,:,:,:) = f(2,1,1,1)
 33:     dfdt_vdp(2,:,:,:) = mu*(one - f(1,1,1,1)**2)*f(2,1,1,1) - f(1,1,1,1)
 34:   end function dfdt_vdp
 35:   !
 36:   ! The standard Forward Euler time-stepping method.
 37:   !
 38:   recursive subroutine forw_euler(t,dt,ib1,ibn,jb1,jbn,kb1,kbn,imax,jmax,kmax,neq,y,dfdt)
 39:     PetscReal, intent(in) :: t,dt
 40:     PetscInt, intent(in) :: ib1,ibn,jb1,jbn,kb1,kbn,imax,jmax,kmax,neq
 41:     PetscReal, dimension(neq,ib1:ibn,jb1:jbn,kb1:kbn), intent(inout) :: y
 42:     !
 43:     ! Define the right-hand side function
 44:     !
 45:     interface
 46:       function dfdt(t,dt,ib1,ibn,jb1,jbn,kb1,kbn,imax,jmax,kmax,n,f)
 47:         PetscReal, intent(in) :: t,dt
 48:         PetscInt, intent(in) :: ib1,ibn,jb1,jbn,kb1,kbn,imax,jmax,kmax,n
 49:         PetscReal, dimension(n,ib1:ibn,jb1:jbn,kb1:kbn), intent(inout) :: f
 50:         PetscReal, dimension(n,imax,jmax,kmax) :: dfdt
 51:       end function dfdt
 52:     end interface
 53:     !--------------------------------------------------------------------------
 54:     !
 55:     y(:,1:imax,1:jmax,1:kmax) = y(:,1:imax,1:jmax,1:kmax)  + dt*dfdt(t,dt,ib1,ibn,jb1,jbn,kb1,kbn,imax,jmax,kmax,neq,y)
 56:   end subroutine forw_euler
 57:   !
 58:   ! The following 4 subroutines handle the mapping of coordinates. I'll explain
 59:   ! this in detail:
 60:   !    PETSc gives you local arrays which are indexed using the global indices.
 61:   ! This is probably handy in some cases, but when you are re-writing an
 62:   ! existing serial code and want to use DMDAs, you have tons of loops going
 63:   ! from 1 to imax etc. that you don't want to change.
 64:   !    These subroutines re-map the arrays so that all the local arrays go from
 65:   ! 1 to the (local) imax.
 66:   !
 67:   subroutine petsc_to_local(da,vec,array,f,dof,stw)
 68:     use petscdmda
 69:     DM                                                            :: da
 70:     Vec,intent(in)                                                :: vec
 71:     PetscReal, pointer                                            :: array(:,:,:,:)
 72:     PetscInt,intent(in)                                           :: dof,stw
 73:     PetscReal, intent(inout), dimension(:,1-stw:,1-stw:,1-stw:) :: f
 74:     PetscErrorCode                                                :: ierr
 75:     !
 76:     PetscCall(DMDAVecGetArrayF90(da,vec,array,ierr))
 77:     call transform_petsc_us(array,f,stw)
 78:   end subroutine petsc_to_local
 79:   subroutine transform_petsc_us(array,f,stw)
 80:     !Note: this assumed shape-array is what does the "coordinate transformation"
 81:     PetscInt,intent(in)                                   :: stw
 82:     PetscReal, intent(in), dimension(:,1-stw:,1-stw:,1-stw:)  :: array
 83:     PetscReal,intent(inout),dimension(:,1-stw:,1-stw:,1-stw:) :: f
 84:     f(:,:,:,:) = array(:,:,:,:)
 85:   end subroutine transform_petsc_us
 86:   subroutine local_to_petsc(da,vec,array,f,dof,stw)
 87:     use petscdmda
 88:     DM                                                    :: da
 89:     Vec,intent(inout)                                     :: vec
 90:     PetscReal, pointer                                    :: array(:,:,:,:)
 91:     PetscInt,intent(in)                                    :: dof,stw
 92:     PetscReal,intent(inout),dimension(:,1-stw:,1-stw:,1-stw:)  :: f
 93:     PetscErrorCode                                        :: ierr
 94:     call transform_us_petsc(array,f,stw)
 95:     PetscCall(DMDAVecRestoreArrayF90(da,vec,array,ierr))
 96:   end subroutine local_to_petsc
 97:   subroutine transform_us_petsc(array,f,stw)
 98:     !Note: this assumed shape-array is what does the "coordinate transformation"
 99:     PetscInt,intent(in)                                     :: stw
100:     PetscReal, intent(inout), dimension(:,1-stw:,1-stw:,1-stw:) :: array
101:     PetscReal, intent(in),dimension(:,1-stw:,1-stw:,1-stw:)      :: f
102:     array(:,:,:,:) = f(:,:,:,:)
103:   end subroutine transform_us_petsc
104: end module ex13f90auxmodule