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().

 11: program ex40f90
 12: #include <petsc/finclude/petscsnes.h>
 13: #include <petsc/finclude/petscdmda.h>
 14:   use petscdmda
 15:   use petscsnes
 16:   implicit none

 18:   SNES snes
 19:   PetscErrorCode ierr
 20:   DM da
 21:   PetscInt ten, two, one
 22:   PetscScalar sone
 23:   Vec x
 24:   external FormFunctionLocal

 26:   PetscCallA(PetscInitialize(ierr))
 27:   ten = 10
 28:   one = 1
 29:   two = 2
 30:   sone = 1.0

 32:   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))
 33:   PetscCallA(DMSetFromOptions(da, ierr))
 34:   PetscCallA(DMSetUp(da, ierr))

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

 38:   PetscCallA(SNESCreate(PETSC_COMM_WORLD, snes, ierr))
 39:   PetscCallA(SNESSetDM(snes, da, ierr))

 41:   PetscCallA(DMDASNESSetFunctionLocal(da, INSERT_VALUES, FormFunctionLocal, 0, ierr))
 42:   PetscCallA(SNESSetFromOptions(snes, ierr))

 44: !      Solve the nonlinear system
 45: !
 46:   PetscCallA(DMCreateGlobalVector(da, x, ierr))
 47:   PetscCallA(VecSet(x, sone, ierr))
 48:   PetscCallA(SNESSolve(snes, PETSC_NULL_VEC, x, ierr))

 50:   PetscCallA(VecDestroy(x, ierr))
 51:   PetscCallA(SNESDestroy(snes, ierr))
 52:   PetscCallA(DMDestroy(da, ierr))
 53:   PetscCallA(PetscFinalize(ierr))
 54: end

 56: subroutine FormFunctionLocal(in, x, f, dummy, ierr)
 57:   use petscdmda
 58:   implicit none
 59:   PetscInt i, j, k, dummy
 60:   DMDALocalInfo in
 61:   PetscScalar x(in%DOF, in%GXS + 1:in%GXS + in%GXM, in%GYS + 1:in%GYS + in%GYM)
 62:   PetscScalar f(in%DOF, in%XS + 1:in%XS + in%XM, in%YS + 1:in%YS + in%YM)
 63:   PetscErrorCode ierr

 65:   do i = in%XS + 1, in%XS + in%XM
 66:     do j = in%YS + 1, in%YS + in%YM
 67:       do k = 1, in%DOF
 68:         f(k, i, j) = x(k, i, j)*x(k, i, j) - 2.0
 69:       end do
 70:     end do
 71:   end do

 73: end

 75: !/*TEST
 76: !
 77: !   test:
 78: !     args: -snes_monitor_short -snes_view -da_refine 1 -pc_type mg -pc_mg_type full -ksp_type fgmres -pc_mg_galerkin pmat
 79: !     requires: !single
 80: !
 81: !TEST*/