When using http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCShellSetApply.html, do I have the guaranty that xout from " PetscErrorCode apply ( PC pc, Vec xin, Vec xout)" has always been previously filled with zeros ? I may have to fill xout by blocks (I would += several possibly overlapping blocks: I need to make sure xout is first filled with zero to get the correct result).
Franck
