1: #include <petsc/finclude/petscdmda.h>
  2: #include <petsc/finclude/petscksp.h>
  3: module ex45fmodule
  4:   use petscmat
  5:   use petscksp
  6:   use petscdmda
  7:   use petscvec
  8:   implicit none

 10: contains

 12:   subroutine ComputeInitialGuess(ksp, b, ctx, ierr)
 13:     PetscErrorCode, intent(out) :: ierr
 14:     KSP ksp
 15:     PetscInt ctx(*)
 16:     Vec b
 17:     PetscScalar, parameter :: h = 0.0

 19:     PetscCall(VecSet(b, h, ierr))
 20:   end subroutine

 22:   subroutine ComputeRHS(ksp, b, unused, ierr)
 23:     PetscErrorCode, intent(out) :: ierr
 24:     KSP ksp
 25:     Vec b
 26:     integer unused(*)
 27:     PetscScalar h, Hx, Hy
 28:     PetscInt mx, my
 29:     DM dm

 31:     PetscCall(KSPGetDM(ksp, dm, ierr))
 32:     PetscCall(DMDAGetInfo(dm, PETSC_NULL_INTEGER, mx, my, PETSC_NULL_INTEGER, PETSC_NULL_INTEGER, PETSC_NULL_INTEGER, PETSC_NULL_INTEGER, PETSC_NULL_INTEGER, PETSC_NULL_INTEGER, PETSC_NULL_DMBOUNDARYTYPE, PETSC_NULL_DMBOUNDARYTYPE, PETSC_NULL_DMBOUNDARYTYPE, PETSC_NULL_DMDASTENCILTYPE, ierr))

 34:     Hx = 1.0/real(mx - 1)
 35:     Hy = 1.0/real(my - 1)
 36:     h = Hx*Hy
 37:     PetscCall(VecSet(b, h, ierr))
 38:   end subroutine

 40:   subroutine ComputeMatrix(ksp, A, B, unused, ierr)
 41:     PetscErrorCode, intent(out) :: ierr
 42:     KSP ksp
 43:     Mat A, B
 44:     integer unused(*)
 45:     DM dm

 47:     PetscInt i, j, mx, my, xm, ym, xs, ys
 48:     PetscScalar v(5), Hx, Hy
 49:     PetscScalar HxdHy, HydHx
 50:     MatStencil row(1), col(5)

 52:     PetscCall(KSPGetDM(ksp, dm, ierr))
 53:     PetscCall(DMDAGetInfo(dm, PETSC_NULL_INTEGER, mx, my, PETSC_NULL_INTEGER, PETSC_NULL_INTEGER, PETSC_NULL_INTEGER, PETSC_NULL_INTEGER, PETSC_NULL_INTEGER, PETSC_NULL_INTEGER, PETSC_NULL_DMBOUNDARYTYPE, PETSC_NULL_DMBOUNDARYTYPE, PETSC_NULL_DMBOUNDARYTYPE, PETSC_NULL_DMDASTENCILTYPE, ierr))

 55:     Hx = 1.0/real(mx - 1)
 56:     Hy = 1.0/real(my - 1)
 57:     HxdHy = Hx/Hy
 58:     HydHx = Hy/Hx
 59:     PetscCall(DMDAGetCorners(dm, xs, ys, PETSC_NULL_INTEGER, xm, ym, PETSC_NULL_INTEGER, ierr))
 60:     do j = ys, ys + ym - 1
 61:       do i = xs, xs + xm - 1
 62:         row(1)%i = i
 63:         row(1)%j = j
 64:         if (i == 0 .or. j == 0 .or. i == mx - 1 .or. j == my - 1) then
 65:           v(1) = 2.0*(HxdHy + HydHx)
 66:           PetscCall(MatSetValuesStencil(B, 1_PETSC_INT_KIND, row, 1_PETSC_INT_KIND, row, v, INSERT_VALUES, ierr))
 67:         else
 68:           v(1) = -HxdHy
 69:           col(1)%i = i
 70:           col(1)%j = j - 1
 71:           v(2) = -HydHx
 72:           col(2)%i = i - 1
 73:           col(2)%j = j
 74:           v(3) = 2.0*(HxdHy + HydHx)
 75:           col(3)%i = i
 76:           col(3)%j = j
 77:           v(4) = -HydHx
 78:           col(4)%i = i + 1
 79:           col(4)%j = j
 80:           v(5) = -HxdHy
 81:           col(5)%i = i
 82:           col(5)%j = j + 1
 83:           PetscCall(MatSetValuesStencil(B, 1_PETSC_INT_KIND, row, 5_PETSC_INT_KIND, col, v, INSERT_VALUES, ierr))
 84:         end if
 85:       end do
 86:     end do
 87:     PetscCall(MatAssemblyBegin(B, MAT_FINAL_ASSEMBLY, ierr))
 88:     PetscCall(MatAssemblyEnd(B, MAT_FINAL_ASSEMBLY, ierr))
 89:     if (A /= B) then
 90:       PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY, ierr))
 91:       PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY, ierr))
 92:     end if
 93:   end subroutine
 94: end module ex45fmodule

 96: program main
 97:   use petscdmda
 98:   use petscksp
 99:   use ex45fmodule
100:   implicit none

102:   PetscInt is, js, iw, jw
103:   PetscErrorCode ierr
104:   KSP ksp
105:   DM dm

107:   PetscCallA(PetscInitialize(ierr))
108:   PetscCallA(KSPCreate(PETSC_COMM_WORLD, ksp, ierr))
109:   PetscCallA(DMDACreate2D(PETSC_COMM_WORLD, DM_BOUNDARY_NONE, DM_BOUNDARY_NONE, DMDA_STENCIL_STAR, 3_PETSC_INT_KIND, 3_PETSC_INT_KIND, PETSC_DECIDE, PETSC_DECIDE, 1_PETSC_INT_KIND, 1_PETSC_INT_KIND, PETSC_NULL_INTEGER_ARRAY, PETSC_NULL_INTEGER_ARRAY, dm, ierr))
110:   PetscCallA(DMSetFromOptions(dm, ierr))
111:   PetscCallA(DMSetUp(dm, ierr))
112:   PetscCallA(KSPSetDM(ksp, dm, ierr))
113:   PetscCallA(KSPSetComputeInitialGuess(ksp, ComputeInitialGuess, 0, ierr))
114:   PetscCallA(KSPSetComputeRHS(ksp, ComputeRHS, 0, ierr))
115:   PetscCallA(KSPSetComputeOperators(ksp, ComputeMatrix, 0, ierr))
116:   PetscCallA(DMDAGetCorners(dm, is, js, PETSC_NULL_INTEGER, iw, jw, PETSC_NULL_INTEGER, ierr))
117:   PetscCallA(KSPSetFromOptions(ksp, ierr))
118:   PetscCallA(KSPSetUp(ksp, ierr))
119:   PetscCallA(KSPSolve(ksp, PETSC_NULL_VEC, PETSC_NULL_VEC, ierr))
120:   PetscCallA(KSPDestroy(ksp, ierr))
121:   PetscCallA(DMDestroy(dm, ierr))
122:   PetscCallA(PetscFinalize(ierr))
123: end

125: !/*TEST
126: !
127: !   test:
128: !      nsize: 4
129: !      args: -ksp_monitor_short -da_refine 5 -pc_type mg -pc_mg_levels 5 -mg_levels_ksp_type chebyshev -mg_levels_ksp_max_it 2 -mg_levels_pc_type jacobi -ksp_pc_side right
130: !
131: !TEST*/