On Fri, 31 May 2013 21:03:51 -0500 Jed Brown <[email protected]> wrote: > Jan Blechta <[email protected]> writes: > > > So you count to ghost values all the items in local form. I thought > > that term `ghost values` means in PETSc only off-process dofs. > > When the discretization looks at a mesh, there is an owned portion and > some "ghost points" that are needed as part of computing a residual or > assembling a nonlinear problem. > > The local vector contains those points, but has no knowledge about the > global domain, nor inherent knowledge of which points are "ghosts". > That structure is up to your application to interpret. > > The global vector contains no information about your discretization, > thus no interpretation of "ghosts". All operations are collective. > > Special global vectors can use VecGhostUpdateBegin/End and > VecGhostGetLocalForm to move between the global and local spaces, but > the objects on either side have live exclusively within their > respective spaces.
Thanks, now I get it. It seems then rather unnecessary that DOLFIN creates ghosted local vector with all the on-process dofs + "ghosts". On-process dofs are then stored twice and must be copied everytime VecGhostUpdateBegin/End is called. > _______________________________________________ > fenics mailing list > [email protected] > http://fenicsproject.org/mailman/listinfo/fenics _______________________________________________ fenics mailing list [email protected] http://fenicsproject.org/mailman/listinfo/fenics
