dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Tue, Sep 06, 2011 at 01:57:20PM -0700, Johan Hake wrote:
> On Tuesday September 6 2011 13:47:02 Anders Logg wrote:
> > On Tue, Sep 06, 2011 at 12:21:03PM -0700, Johan Hake wrote:
> > > On Tuesday September 6 2011 12:18:33 Anders Logg wrote:
> > > > On Tue, Sep 06, 2011 at 11:31:03AM -0700, Johan Hake wrote:
> > > > > 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 <johan.hake@xxxxxxxxx>
> 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);
> > > >
> > > > Yes, that is the intention! Thanks for proofreading my code before
> > > > I've even had a chance to test it. :-)
> > > :
> > > :)
> > >
> > > You gave the impression that it was test when you asked me to wrap it to
> > > Python. Give me a ping when it is ready and I will have a bite at the
> > > SWIG code.
> >
> > I wanted the Python wrappers so that I could write the unit tests for
> > it (in Python) and then find the bugs... :-)
>
> Ahhh!
>
> You fix the backward compatability of the file format of the MeshFunction and
> I start on the SWIG code. Deal?

Deal! But not until after tomorrow. I have a paper I need to revise.

--
Anders