[petsc-users] Fortran Example problem with MPI_COMM_WORLD

[Jed Brown]

Inge Gutheil <i.gutheil at fz-juelich.de> writes:

> Hello,
> in
>
> petsc-3.4.2/src/snes/examples/tests/ex12f.F it says
>    8 !  In this example the application context is a Fortran integer array:
>    9 !      ctx(1) = da    - distributed array
>   10 !          2  = F     - global vector where the function is stored
>   11 !          3  = xl    - local work vector
>   12 !          4  = comm  - MPI communictor
>   13 !          5  = unused
>   14 !          6  = N     - system size
>
> This array is declared as
> 34       PetscFortranAddr ctx(6)

True, this is not portable.  F77 is terrible, but we can fix this
example by getting rid of the last three fields, instead opting for

  MPI_Comm comm
  call PetscObjectGetComm(da,comm,ierr)
  call VecGetSize(F,N,ierr)


Also, this is totally bogus:

! Write results if first processor
      if (ctx(4) .eq. 0) then
        write(6,100) its
      endif


Thanks for finding this.
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