On Mon, Jan 28, 2013 at 10:33:15PM +0000, Garth N. Wells wrote: > On 28 January 2013 22:27, Anders Logg <[email protected]> wrote: > > On Mon, Jan 28, 2013 at 11:19:13PM +0100, Johan Hake wrote: > >> On 01/28/2013 11:08 PM, Anders Logg wrote: > >> > On Mon, Jan 28, 2013 at 10:37:46PM +0100, Johan Hake wrote: > >> >> On 01/28/2013 10:22 PM, Anders Logg wrote: > >> >>> On Mon, Jan 28, 2013 at 10:10:40PM +0100, Johan Hake wrote: > >> >>>> Hello! > >> >>>> > >> >>>> I have now added a method to DofMap, which tabulate a map between > >> >>>> vertices and dofs. It will only work for DofMaps with dofs on > >> >>>> vertices. > >> >>>> So basically for any CG 1 FunctionSpaces and will raise error else > >> >>>> wise. > >> >>>> > >> >>>> Usage: > >> >>>> > >> >>>> from dolfin import * > >> >>>> import numpy as np > >> >>>> mesh = UnitSquareMesh(10,10) > >> >>>> V = VectorFunctionSpace(mesh, "CG", 1) > >> >>>> u = Function(V) > >> >>>> u.interpolate(Constant((1,2))) > >> >>>> vert_values = np.zeros(mesh.num_vertices()*2) > >> >>>> vert_values[V.dofmap().tabulate_vertex_map(mesh)] = \ > >> >>>> u.vector().array() > >> >>>> print vert_values > >> >>>> > >> >>>> In parallel the map will follow the local dofs. This means that some > >> >>>> values in vert_values above will still be 0. The 0 values will then > >> >>>> correspond to vertex values which are owned by another process. > >> >>>> > >> >>>> In C++ the method returns a std::vector<std::size_t>. > >> >>>> > >> >>>> Questions: > >> >>>> Does the name "tabulate_vertex_map" work? > >> >>> > >> >>> Sounds ok. > >> >>> > >> >>>> Should a version of this method exist in other classes. FunctionSpace, > >> >>>> Function (without the mesh argument of course)? > >> >>> > >> >>> Yes, would be good to have for convenience. > >> >>> > >> >>> What is the relation to Function::compute_vertex_values? > >> >> > >> >> compute_vertex_values works on any GenericFunction. However, for all > >> >> Functions from CG 1 families I guess one could use this map to just > >> >> tabulate the entries. > >> > > >> > What does the tabulate_vertex_map method do which > >> > compute_vertex_values doesn't? Enable writing to dofs? > >> > >> RTFC! ;) > >> > >> tabulate_vertex_map only computes a map based on the prior knowledge of > >> the dofs coinciding with the vertices. compute_vertex_values are much > >> more general and used > >> > >> element.interpolate_vertex_values > >> > >> to do the heavy lifting. > > > > Yes, so why is tabulate_vertex_map needed, if compute_vertex_values > > already computes the vertex values and is much more general? > > > >> I see tabulate_vertex_map as a convenience mapping for users who want > >> their data on a vertex based format, or users who want data which > >> resides on vertices into dolfin la structures. > > > > What is the use case? If it is for plotting or postprocessing, then > > compute_vertex_values should be enough. > > > > Or is the intention to use it for modifying values of CG1 functions > > from the outside? > > > > I don't think that it's required, but I guess Johan is adding it by > popular demand.
I'm not objecting to it. I just came to think about the compute_vertex_values function and it should be enough to cover most of the use cases that are the background for the popular demand: users of Hans Petter's tutorial who want to get the vertex values on a regular grid for postprocessing in external software like MATLAB. -- Anders _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
