On 6 September 2011 19:16, Anders Logg <[email protected]> wrote: > On Tue, Sep 06, 2011 at 07:14:01PM +0100, Garth N. Wells wrote: >> On 6 September 2011 19:04, Anders Logg <[email protected]> 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. >> > >> >> Because 'markers' leads one to believe that it's a boolean or integer. > > ok. > >> >> > 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. >> > >> >> No need for a look up, just iterate over the map. > > Then why do we need a map? >
Because the object maps a pair to a value. A std::vector would allow multiple entries with the same (uint, uint) pair, which is ambiguous. If we want, for example, to apply a bc based on a 'marker' we can iterate over the markers and get the value, and then depending on the marker do something. >> >> > 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. >> > >> >> Could you be precise about which class functions belong to and the >> argument types for the above point? > > I don't understand the question. > Function signature. Garth > -- > Anders > > >> Garth >> >> >> >> 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. >> > >> > > _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
