On Tuesday September 6 2011 11:04:23 Anders Logg wrote: > On Tue, Sep 06, 2011 at 05:45:33PM +0100, Garth N. Wells wrote: > > On 6 September 2011 17:31, Johan Hake <[email protected]> wrote: > > > On Monday September 5 2011 00:09:58 Anders Logg wrote: > > >> On Sun, Sep 04, 2011 at 11:23:04PM -0700, Johan Hake wrote: > > >> > On Friday September 2 2011 23:19:22 Anders Logg wrote: > > >> > > On Fri, Sep 02, 2011 at 02:35:57PM -0700, Johan Hake wrote: > > >> > > > What is the different between a MeshMarker and a MeshFunction? > > >> > > > Is MeshMarker a MeshFunction but instead of storing the values > > >> > > > in line with its global entity index it stores it wrt the > > >> > > > global cell entity index together with its local entity index? > > >> > > > > >> > > Yes, that and values don't need to be stored on the entire mesh, > > >> > > only for a subset, so you can mark just 3 facets without needing > > >> > > to store markers for a million facets. > > >> > > > >> > ok, I will see what I can do. > > >> > > >> Thanks! > > >> > > >> > > Copy paste from the MeshMarker docstring: > > >> > > /// The MeshMarkers class can be used to store data associated > > >> > > with /// a subset of the entities of a mesh of a given > > >> > > topological /// dimension. It differs from the MeshFunction class > > >> > > in two ways. /// First, data does not need to be associated with > > >> > > all entities /// (only a subset). Second, data is associated with > > >> > > entities /// through the corresponding cell index and local > > >> > > entity number /// (relative to the cell), not by global entity > > >> > > index, which means /// that data may be stored robustly to file. > > >> > > > > >> > > > Also, will this take over for the way we use MeshFunctions in > > >> > > > the assembler, or will a MeshFunction be generated by a > > >> > > > MeshMarker before assemble gets called? > > >> > > > > >> > > I think we will do that as a first step (convert from MeshMarker > > >> > > to MeshFunction) since then we don't need to touch the assembler. > > >> > > Then later we can think about using MeshMarkers directly. > > >> > > > >> > Ok. > > >> > > > >> > > > I think I also get confused with the naming here. If my > > >> > > > explaination of what MeshMarker is doing is correct, a > > >> > > > MeshMarker and a MeshFunction are essentially doing the same > > >> > > > thing. What differs is the way the data is stored. This is not > > >> > > > reflected in the naming of the classes > > >> > > > > >> > > It was the best I could come up with. Feel free to suggest > > >> > > something else. SubsetMeshFunction would also be confusing since > > >> > > it's not really a MeshFunction. > > >> > > > > >> > > Either way, I expect the MeshMarkers class to be used mostly > > >> > > internally by the MeshDomains class. > > >> > > > >> > Ok. > > >> > > > >> > Not sure these are better, but they might reflect the difference > > >> > between this guy and a MeshFunction in a slightly more intuitive > > >> > way. > > >> > > > >> > MeshEntityFunction, LocalMeshEntityFunction, LocalMeshFunction, > > >> > SubMeshFunction > > >> > > >> I'm not sure those are much better, and I don't think it would be > > >> correct to call them something containing "Function" since they are > > >> not really functions. With a MeshFunction, one can input x (a mesh > > >> entity) and get y = f(x) (the value of the MeshFunction at that > > >> entity). That's not possible with MeshMarkers; they are just a > > >> collection of markers, not really a function since the value is only > > >> defined on a subset and one would need to loop through the list of > > >> values to get the value at any entity where the value is actually > > >> defined. > > > > > > What with MeshValueCollection? As it is a templated class I do not > > > think Marker is an appropriated name. > > > > Agree. > > > > > 'Collection' says that the class is not > > > defined over the whole Mesh. > > I don't see what the templating has to do with the name "markers" but > MeshValueCollection sounds good. > > > > Two questions: > > > > > > How can the following code work: > > > > > > // Get marker data > > > const std::vector<uint>& marker = _markers[i]; > > > const uint cell_index = marker[0]; > > > const uint local_entity = marker[1]; > > > const T marker_value = marker[2]; > > > > > > when _markers is declared as: > > > > > > // The markers > > > std::vector<std::pair<std::pair<uint, uint>, T> > _markers; > > The above code doesn't work. I suspect the code hasn't yet been > instantiated so it wasn't detected by the compiler. > > The markers need to be accessed as follows (from XMLMeshMarkers.h): > > for (uint i = 0; i < mesh_markers.size(); ++i) > { > pugi::xml_node entity_node = mf_node.append_child("marker"); > const std::pair<std::pair<uint, uint>, T>& marker = > mesh_markers.get_marker(i); > entity_node.append_attribute("cell_index") = marker.first.first; > entity_node.append_attribute("local_entity") = marker.first.second; > entity_node.append_attribute("marker_value") = marker.second; > } > > > The above also permits multiple entries. Perhaps we want > > > > boost::unordered_map<std::pair<std::pair<uint, uint>, T> > _markers; > > Yes, maybe but I'm not sure what the cost would be for the lookup on > each cell during assembly. > > > > What is the logic behind: > > > > > > // Set all value of mesh function to maximum value (not all will > > > // be set) by markers below > > > mesh_function.set_all(maxval); > > > > > > Isn't it more natural to initiate the values to zero? Also it makes no > > > sense in conjunction with boundary markers. Then all boundary faces > > > gets marked with the largest marker value. I cannot see how that could > > > be correct. > > > > I don't get ' mesh_function.set_all(maxval);' or the code comment. > > The point is that one should be able to define a form with domains say > dx(0), dx(1) and dx(2) and then have a mesh file that marks a subset > of the cells with '0', '1' and '2'. > > Then the conversion to MeshFunction inserts '3' for all other > (unmarked) cells. This allows a user to specify only the interesting > cells and no need to mark the rest with -1 or None or similar.
That would make sense if the code would be: mesh_function.set_all(maxval+1); Johan > > >> So MeshMarkers may not be that bad. I'm starting to get used to > > >> it... :-) > > > > > > That's what worries me :) > > > > Me too (worried, that is). > > Don't worry. > > -- > Anders _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
