Date: 2026-03-01T05:25:08+00:00

Actual source code: ex40f90.F90

      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*/