dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, Dec 08, 2008 at 08:01:32AM +0100, Johan Hake wrote:
> On Sunday 07 December 2008 23:33:53 Anders Logg wrote:
> > Something that needs to be added to the new Function interface is
> > reading functions from file. This has worked before:
> >
> >   f = Function("function.xml")
> >
> > Can this be added to the metaclass machinery?
> 
> No, but to the __new__ function ;) so I guess yes!
> 
> The metalclass produces Function classes. The __new__ function instantiate new 
> Functions from what ever argument. This is such a case.

It looks like some work is needed to get this in place.

The "constructor" currently looks as follows:

    def __new__(cls, V, **kwargs):

so to do

    f = Function("function.xml")

we need to check if V is a string. Could you add some hooks for this?

Also, we need to figure out how to define the file format for
Functions.

Currently, it looks like this:

<dolfin ...>
  <function> 
    <mesh ...>
      ...
    </mesh>
    <vector ...>
      ...
    </vector>
    <finiteelement signature="..."/>
    <dofmap signature="..."/>
  </function> 
</dolfin>

Should we change the file format to reflect the new design? We would
need something like this:

<dolfin ...>
  <function> 
    <functionspace>
      <mesh>
        ...
      </mesh>
      <finiteelement signature="..."/>
      <dofmap signature="..."/>
    </functionspace>
    <vector ...>
      ...
    </vector>
  </function> 
</dolfin>

We also need to change the signature strings so that one may
create form compiler elements (and dofmaps) from the strings.

The simplest option could be to let the signature be something like

   FiniteElement("Lagrange", "triangle", 1)

so that we may create the objects using exec() directly on the
strings, perhaps prepended with the name of the form compiler:

   ffc.FiniteElement("Lagrange", "triangle", 1)

This will be supported through __repr__ which is implemented correctly
in UFL (but not in FFC).

If this looks reasonable, could you take a look to see what's needed
on the Python side and I can take a look at updating the XML format?

-- 
Anders

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