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:             enddo
 70:          enddo
 71:       enddo

 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*/