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: #include <petsc/finclude/petscdmda.h>
 10:     use petscdm
 11:     DMBoundaryType,intent(inout) :: b_x,b_y,b_z

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

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