[petsc-users] Question on DMMGSetSNESLocal from snes/example/tutorials/ex19.c

[Jed Brown]

"Sun, Hui" <hus003 at ucsd.edu> writes:

> Continue this topic. Right now I'm looking at ex19.c from PETSc v3.3
> and v3.4, both containing a user defined function NonlinearGS(SNES,
> Vec, Vec, void*), I'm wondering why the arguments are not passed by
> reference or pointers? 

All PETSc objects (like SNES, Vec, etc.) are pointers to private
structures.

  typedef struct _p_Vec *Vec;

You cannot dereference the pointer because the implementation is
private, but it is passed around as a pointer.
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