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

 13: #include <petsc/finclude/petscsnes.h>
 14: #include <petsc/finclude/petscdmda.h>
 15:       use petscsnes
 16:       use petscdmda
 17:       implicit none

 19:       SNES             snes
 20:       PetscErrorCode   ierr
 21:       DM               da
 22:       PetscInt         ten,two,one
 23:       external         FormFunctionLocal

 25:       PetscCallA(PetscInitialize(ierr))
 26:       ten = 10
 27:       one = 1
 28:       two = 2

 30:       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,PETSC_NULL_INTEGER,da,ierr))
 31:       PetscCallA(DMSetFromOptions(da,ierr))
 32:       PetscCallA(DMSetUp(da,ierr))

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

 36:       PetscCallA(SNESCreate(PETSC_COMM_WORLD,snes,ierr))
 37:       PetscCallA(SNESSetDM(snes,da,ierr))

 39:       PetscCallA(DMDASNESSetFunctionLocal(da,INSERT_VALUES,FormFunctionLocal,0,ierr))
 40:       PetscCallA(SNESSetFromOptions(snes,ierr))

 42: !      Solve the nonlinear system
 43: !
 44:       PetscCallA(SNESSolve(snes,PETSC_NULL_VEC,PETSC_NULL_VEC,ierr))

 46:       PetscCallA(SNESDestroy(snes,ierr))
 47:       PetscCallA(DMDestroy(da,ierr))
 48:       PetscCallA(PetscFinalize(ierr))
 49:       end

 51:       subroutine FormFunctionLocal(in,x,f,dummy,ierr)
 52:       implicit none
 53:       PetscInt i,j,k,dummy
 54:       DMDALocalInfo in(DMDA_LOCAL_INFO_SIZE)
 55:       PetscScalar x(in(DMDA_LOCAL_INFO_DOF),XG_RANGE,YG_RANGE)
 56:       PetscScalar f(in(DMDA_LOCAL_INFO_DOF),X_RANGE,Y_RANGE)
 57:       PetscErrorCode ierr

 59:       do i=in(DMDA_LOCAL_INFO_XS)+1,in(DMDA_LOCAL_INFO_XS)+in(DMDA_LOCAL_INFO_XM)
 60:          do j=in(DMDA_LOCAL_INFO_YS)+1,in(DMDA_LOCAL_INFO_YS)+in(DMDA_LOCAL_INFO_YM)
 61:             do k=1,in(DMDA_LOCAL_INFO_DOF)
 62:                f(k,i,j) = x(k,i,j)*x(k,i,j) - 2.0
 63:             enddo
 64:          enddo
 65:       enddo

 67:       return
 68:       end

 70: !/*TEST
 71: !
 72: !   test:
 73: !     args: -snes_monitor_short -snes_view -da_refine 1 -pc_type mg -pc_mg_type full -ksp_type fgmres -pc_mg_galerkin pmat
 74: !     requires: !single
 75: !
 76: !TEST*/