dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Monday August 16 2010 10:57:25 Garth N. Wells wrote:
> While you're at it with wrapping MeshFunction, I added
> 
>     MeshFunction(const Mesh& mesh, uint dim, const T& value)
> 
> a while ago (not the const T& value at the end). It would be nice if
> this could be used from Python too. Saves calling the 'set' function.

That would be usefull! 

Then I suggest we get rid of the required type information. We can default to 
"uint". 

 MeshFunction(mesh, 0, 1)

would return a VertexFunction of uints initiated to 1. If float is wanted one 
can do:

  MeshFunction(mesh, 0, 1, "d")

or

  MeshFunction(mesh, 0, 1.0)

An unintialized MeshFunction of int would have to be something like:

  MeshFunction(mesh, 0, dtype="i")

or 

  MeshFunction(mesh, 0, 0, "i")

This would then be similare to NumPy. When you call zeros(4), you get an array 
of floats by default.

What you say?

Johan

> Garth
> 
> On Mon, 2010-08-16 at 10:53 -0700, Johan Hake wrote:
> > On Monday August 16 2010 10:34:01 Anders Logg wrote:
> > > On Mon, Aug 16, 2010 at 10:28:10AM -0700, Johan Hake wrote:
> > > > On Monday August 16 2010 10:07:41 Anders Logg wrote:
> > > > > On Mon, Aug 16, 2010 at 09:57:26AM -0700, Johan Hake wrote:
> > > > > > On Monday August 16 2010 05:51:24 noreply@xxxxxxxxxxxxx wrote:
> > > > > > > ------------------------------------------------------------
> > > > > > > revno: 4986
> > > > > > > committer: Anders Logg <logg@xxxxxxxxx>
> > > > > > > branch nick: dolfin-dev
> > > > > > > timestamp: Mon 2010-08-16 14:48:44 +0200
> > > > > > > 
> > > > > > > message:
> > > > > > >   Implement named MeshFunctions in Python. Might be a better
> > > > > > >   way (using
> > > > > > > 
> > > > > > > SWIG magic).
> > > > > > 
> > > > > > I think it is fine. The only reason we would like to wrap it
> > > > > > using SWIG would be to preserve the types. So one could check if
> > > > > > a passed MeshFunction is for example a VertexFunction. But I
> > > > > > think we should not encourage that and instead use dim.
> > > > > 
> > > > > ok.
> > > > > 
> > > > > > When I looked at the Python implementation I wonder if we should
> > > > > > harmonize the data type setting with NumPy. Instead of 'int' pass
> > > > > > either int or 'i', and so on.
> > > > > > 
> > > > > > If you agree, do you know of any other place where we could do
> > > > > > such a harmonizing?
> > > > > 
> > > > > Isn't the problem that with "uint" we get the expected type (that
> > > > > matches dolfin::uint in C++). Last time I checked, the NumPy list
> > > > > of int types is a jungle of different options.
> > > > 
> > > > Yes, but we have setled in the NumPy typemaps on the correct one. It
> > > > is to use "I" or unit32 for unsigned int. This will not be any
> > > > problem eitherway as these types are just used to instantiate the
> > > > correct MeshFunctionFoo. in the same "switch" statement we have now.
> > > 
> > > I imagine "uint" is easier since that is used in C++, or maybe it's
> > > simple for me because I'm working on the DOLFIN C++ code and see a lot
> > > of "uint"...
> > 
> > Maybe I am confused because I always think in typical numpy types. Then I
> > can add the possibility to use the NumPy types while keeping the old
> > ones?
> > 
> > > > > > I also think it is better to implement the named MeshFunctions as
> > > > > > inheriting from MeshFunction, instead of just beeing functions
> > > > > > that returns. I can fix this.
> > > > > 
> > > > > I tried but it didn't work (the constructors were not called) but
> > > > > I'm sure you know how to fix it. :-)
> > > > 
> > > > Just use __new__:
> > > >   class VertexFunction(MeshFunction):
> > > >     "Create MeshFunction of topological dimension 0 on given mesh."
> > > >     
> > > >     def __new__(self, value_type, mesh):
> > > >         return MeshFunction.__new__(self, value_type, mesh, 0)
> > > 
> > > Why?
> > 
> > I assume you tried using __init__? Something like:
> >  class VertexFunction(MeshFunction):
> >     "Create MeshFunction of topological dimension 0 on given mesh."
> >     
> >     def __init__(self, value_type, mesh):
> >         MeshFunction.__init__(self, value_type, mesh, 0)
> > 
> > An __init__ method is only called if the object returned from __new__,
> > which is called implicitly befor __init__, is of the _same_ type as the
> > class we are defining. As VertexFunction inherit MeshFunction its
> > __new__ will eventually be called together with the provided arguments,
> > which is for example
> > 
> >    "uint", mesh
> > 
> > What MeshFunction.__new__ returns are then an empty MeshFunctionUInt,
> > because this is what MeshFunctions("uint", mesh) gives you. As
> > MeshFunctionUInt is not of the same type as MeshFunction or
> > VertexFunction, its __init__ will not be called and we will get an empty
> > meshfunction.
> > 
> > If we instead overload __new__ we can manipulate what is returned from
> > the class initialization. Instead of calling MeshFunction.__new__
> > VertexFunction.__new__ is called.
> > 
> > Comprendo?
> > 
> > Johan
> > 
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