Hi,
I'm familiar with these two maps since I use them for a gradient
recovery technique.
I can assure you that first time I used vertex_to_dof_map I was a bit
confused,
since the convention should be left to right (as Garth pointed out).
Example: eps2pdf fig.eps ---> fig.pdf
vertex2dof vertex_id --> dof_id
dof2vertex dof_id --> vertex_id
So at the moment is really confusing. Maybe we can introduce new functions
{vertex2dof,dof2vertex}_map
(no name collision) and deprecate the old one, so the user is aware of the
change but its code doesn't brake.
Simone
2013/8/31 Jan Blechta <[email protected]>
> On Fri, 30 Aug 2013 23:47:35 +0100
> "Garth N. Wells" <[email protected]> wrote:
>
> > On 30 August 2013 23:37, Johan Hake <[email protected]> wrote:
> > > On Friday August 30 2013 23:19:09 Garth N. Wells wrote:
> > >> On 30 August 2013 22:50, Johan Hake <[email protected]> wrote:
> > >> > On Friday August 30 2013 15:47:28 Garth N. Wells wrote:
> > >> >> The functions GenericDofmap::vertex_to_dof_map and
> > >> >> GenericDofMap::dof_to_vertex_map are not properly documented
> > >> >> (the doc string is the same for both), and I think that they
> > >> >> are back to front. The docstring in DofMap has inconsistencies.
> > >> >> I would expect that
> > >> >>
> > >> >> map0 = GenericDofmap::vertex_to_dof_map(...)
> > >> >>
> > >> >> would mean a map from vertex to dof, i.e.
> > >> >>
> > >> >> map0[vertex_index] -> dof index
> > >> >>
> > >> >> and that
> > >> >>
> > >> >> map1 = GenericDofmap::dof_to_vertex_map(...)
> > >> >>
> > >> >> would mean a map from dof index to
> > >> >>
> > >> >> map1[dof_index] -> vertex index
> > >> >>
> > >> >> Tests (see below code) and the return types also indicate that
> > >> >> things are back to front. Can someone clarify the situation?
> > >> >
> > >> > The map was introduced to help a user map vertex based data onto
> > >> > a Function.>
> > >> > from dolfin import *
> > >> > import numpy as np
> > >> >
> > >> > mesh = UnitSquareMesh(20,20)
> > >> > V = VectorFunctionSpace(mesh, "CG", 1)
> > >> > u = Function(V)
> > >> > vertex_to_dof_map = V.dofmap().vertex_to_dof_map(mesh)
> > >> >
> > >> > data = np.reshape(mesh.coordinates()[:],
> > >> > (mesh.num_vertices()*2)) u.vector()[:] = data[vertex_to_dof_map]
> > >> > plot(u, interactive=True)
> > >> >
> > >> > The size of the data array should be:
> > >> > mesh.num_vertices()*u.value_size()
> > >> >
> > >> > The documentation should be improved, and not least properly
> > >> > mapped from C++ to Python.
> > >> >
> > >> > The name refer to the mapping that turn vertex based data to dof
> > >> > based and reads quite well when used as above. I can see that
> > >> > the word map can be missleading. It is not a "map" data
> > >> > structure. It is an index set that "maps values".
> > >> >
> > >> > Still confused?
> > >>
> > >> I'm not confused. It's clear that the function names are
> > >> back-to-front. It doesn't matter what they were included for - they
> > >> are members of GenericDofMap and must make sense in that context.
> > >>
> > >> Since reading from left to right is a well established convention,
> > >> I propose that (a) the function names be fixed by reversing them;
> > >> and (b) the doc strings be fixed.
> > >
> > > Agree on (b). I am not fully convinced by (a).
> > >
> > > I am not sure what your example tries to show. You are not using
> > > the mapping the intended way and I am therefore confused about the
> > > whole back-to-front, front-to-back discussion.
> >
> > Just read the function names aloud from left to right -
> > 'vertex_to_dof_map' should be a 'vertex to dof map', i.e. a map from a
> > vertex *to* a dof.
>
> Just read from left to right - 'vertex_to_dof_map' stands for a map
> which turns a vertex map into a dof map (when used as a right
> composition).
>
> Yes, I was confused at first when I saw this and agree with Garth it
> should be 'left to right'. But does it worth switching it? Is the whole
> concept of indexing by
>
> vertex_index*dofs_per_vertex+local_dof
>
> sustainable? Or should it be replaced by some more robust types which
> would handle non-injective map (and its inversion)?
>
> There were some user codes using these functions as seen in discussions.
>
> Jan
>
> >
> > Garth
> >
> >
> > >
> > > Johan
> > >
> > >> Garth
> > >>
> > >> > Johan
> > >> >
> > >> >> Garth
> > >> >>
> > >> >>
> > >> >>
> > >> >> from dolfin import *
> > >> >>
> > >> >> mesh = UnitSquareMesh(4, 4)
> > >> >> V = FunctionSpace(mesh, "Lagrange", 1)
> > >> >>
> > >> >> dof_to_vertex = V.dofmap().dof_to_vertex_map(mesh)
> > >> >> vertex_to_dof = V.dofmap().vertex_to_dof_map(mesh)
> > >> >>
> > >> >> for c in cells(mesh):
> > >> >> print "Cell index:", c.index()
> > >> >>
> > >> >> # Get cell dofs
> > >> >> dofs = V.dofmap().cell_dofs(c.index())
> > >> >> print " Cell dofs:", dofs
> > >> >>
> > >> >> # Get vertices from cell
> > >> >> cell_vertices0 = sorted([v.index() for v in vertices(c)])
> > >> >> print " Cell vertex indices (from cell):", cell_vertices0
> > >> >>
> > >> >> # Get vertices from dof_to_vertex
> > >> >> cell_vertices1 = sorted([dof_to_vertex[dof] for dof in
> > >> >> dofs]) print " Cell vertex indices (from dof_to_vertex_map):",
> > >> >> cell_vertices1
> > >> >>
> > >> >> # Get vertices from vertex_to_dof_map
> > >> >> cell_vertices2 = sorted([vertex_to_dof[dof] for dof in
> > >> >> dofs]) print " Cell vertex indices (from vertex_to_dof_map):",
> > >> >> cell_vertices2
> > >> >>
> > >> >> _______________________________________________
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