1: !
  2: !  Demonstrates use of DMDASNESSetFunctionLocal() from Fortran
  3: !
  4: !    Note: the access to the entries of the local arrays below use the Fortran
  5: !   convention of starting at zero. However calls to MatSetValues()  start at 0.
  6: !   Also note that you will have to map the i,j,k coordinates to the local PETSc ordering
  7: !   before calling MatSetValuesLocal(). Often you will find that using PETSc's default
  8: !   code for computing the Jacobian works fine and you will not need to implement
  9: !   your own FormJacobianLocal().
 10: #include <petsc/finclude/petscsnes.h>
 11: #include <petsc/finclude/petscdmda.h>
 12: module ex40f90module
 13:   use petscdmda
 14:   implicit none
 15: contains
 16:   subroutine FormFunctionLocal(in, x, f, dummy, ierr)
 17:     PetscInt i, j, k, dummy
 18:     DMDALocalInfo in
 19:     PetscScalar x(in%DOF, in%GXS + 1:in%GXS + in%GXM, in%GYS + 1:in%GYS + in%GYM)
 20:     PetscScalar f(in%DOF, in%XS + 1:in%XS + in%XM, in%YS + 1:in%YS + in%YM)
 21:     PetscErrorCode ierr

 23:     do i = in%XS + 1, in%XS + in%XM
 24:       do j = in%YS + 1, in%YS + in%YM
 25:         do k = 1, in%DOF
 26:           f(k, i, j) = x(k, i, j)*x(k, i, j) - 2.0
 27:         end do
 28:       end do
 29:     end do

 31:   end
 32: end module ex40f90module

 34: program ex40f90
 35:   use petscdmda
 36:   use petscsnes
 37:   use ex40f90module
 38:   implicit none

 40:   SNES snes
 41:   PetscErrorCode ierr
 42:   DM da
 43:   PetscInt ten, two, one
 44:   PetscScalar sone
 45:   Vec x

 47:   PetscCallA(PetscInitialize(ierr))
 48:   ten = 10
 49:   one = 1
 50:   two = 2
 51:   sone = 1.0

 53:   PetscCallA(DMDACreate2d(PETSC_COMM_WORLD, DM_BOUNDARY_NONE, DM_BOUNDARY_NONE, DMDA_STENCIL_BOX, ten, ten, PETSC_DECIDE, PETSC_DECIDE, two, one, PETSC_NULL_INTEGER_ARRAY, PETSC_NULL_INTEGER_ARRAY, da, ierr))
 54:   PetscCallA(DMSetFromOptions(da, ierr))
 55:   PetscCallA(DMSetUp(da, ierr))

 57: !       Create solver object and associate it with the unknowns (on the grid)

 59:   PetscCallA(SNESCreate(PETSC_COMM_WORLD, snes, ierr))
 60:   PetscCallA(SNESSetDM(snes, da, ierr))

 62:   PetscCallA(DMDASNESSetFunctionLocal(da, INSERT_VALUES, FormFunctionLocal, 0, ierr))
 63:   PetscCallA(SNESSetFromOptions(snes, ierr))

 65: !      Solve the nonlinear system
 66: !
 67:   PetscCallA(DMCreateGlobalVector(da, x, ierr))
 68:   PetscCallA(VecSet(x, sone, ierr))
 69:   PetscCallA(SNESSolve(snes, PETSC_NULL_VEC, x, ierr))

 71:   PetscCallA(VecDestroy(x, ierr))
 72:   PetscCallA(SNESDestroy(snes, ierr))
 73:   PetscCallA(DMDestroy(da, ierr))
 74:   PetscCallA(PetscFinalize(ierr))
 75: end

 77: !/*TEST
 78: !
 79: !   test:
 80: !     args: -snes_monitor_short -snes_view -da_refine 1 -pc_type mg -pc_mg_type full -ksp_type fgmres -pc_mg_galerkin pmat
 81: !     requires: !single
 82: !
 83: !TEST*/