[petsc-users] Append vector to existing file

[Yuyun Yang via petsc-users]

Hello team,

This is a very simple question, but I just want to be sure I understand how the 
viewer works. I have a file with some vectors already written into it. Now I'm 
calling PetscViewerASCIIOpen, setting the format and then the file mode into 
append:
  PetscViewer viewer;
  ierr = PetscViewerASCIIOpen(PETSC_COMM_WORLD, filename.c_str(), &viewer);
  ierr = PetscViewerPushFormat(viewer, PETSC_VIEWER_ASCII_MATLAB); 
CHKERRQ(ierr);
ierr = PetscViewerFileSetMode(viewer, FILE_MODE_APPEND); CHKERRQ(ierr);

After which I call VecView to append some new vectors to the existing file. But 
this operation is clearing out my existing file and writing it with new 
information. Does the append mode happen to not work with this type of viewer, 
or am I missing something here?

Thanks a lot,
Yuyun