On Mon, Jun 27, 2016 at 10:24 AM, 张江 <[email protected]> wrote:
> Hi,
>
> I have a few questions about reading data in parallel using libmesh. The
> program is running on n processes, and I wish to have n partitions on this
> mesh which means each data partition is assigned to one process.
>
> 1. How to make sure that each process just contains one part of the entire
> mesh and the corresponding nodal values?
> 2. How can each process maintain the data values of ghost nodes since its
> local elements may contains the nodes that are not in its local nodes?
>
> Here is the initialization code. It seems that each process can access the
> entire mesh and the entire nodal solution. Does it mean that each process
> hold the entire data?
>
I'm not sure what reason you have for thinking this... if you look at the
code for ExodusII_IO::copy_nodal_solution() you can see that it reads the
nodal values on every processor, but it only sets the values for which it
is responsible.
Generally speaking, you should only access dofs which fall in the half-open
range
[system.solution->first_local_index(), system.solution->last_local_index())
libMesh::UnstructuredMesh *_mesh;
> libMesh::ExodusII_IO *_exio;
> libMesh::EquationSystems *_eqsys;
> libMesh::System *_asys;
> libMesh::PointLocatorTree *_locator;
>
> _mesh = new Mesh(comm());
> _exio = new ExodusII_IO(*_mesh);
> _exio->read(filename);
> _mesh->allow_renumbering(false);
> _mesh->prepare_for_use();
>
General comment: don't use "new" and "delete" unless you have an explicit
reason for doing so.
>
> unsigned int _Vx_var, _Vy_var, _Vz_var;
> _eqsys = new EquationSystems(*_mesh);
> _asys = &(_eqsys->add_system<System>("Velocity"));
> _Vx_var = _asys->add_variable("Vx", FIRST, LAGRANGE);
> _Vy_var = _asys->add_variable("Vy", FIRST, LAGRANGE);
> _Vz_var = _asys->add_variable("Vz", FIRST, LAGRANGE);
>
> _eqsys->init();
>
> _locator = new PointLocatorTree(*_mesh);
>
> _exio->copy_nodal_solution(*_asys, "Vx", varnames[0]); // velocityX
> _exio->copy_nodal_solution(*_asys, "Vy", varnames[1]); // velocityY
> _exio->copy_nodal_solution(*_asys, "Vz", varnames[2]); // velocityZ
>
> libMesh::UniquePtr<libMesh::NumericVector<libMesh::Number> > _as =
> _asys->current_local_solution->clone();
>
You are making a copy of the entire current_local_solution vector here,
which is almost certainly not what you want.
--
John
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