dolfin team mailing list archive

[David Beacham <d.beacham07@xxxxxxxxxxxxxx>]

Johan Hake wrote:
> On Thursday 17 December 2009 03:13:13 David Beacham wrote:
>   
> > Johan Hake wrote:
> >     
> > > On Wednesday 16 December 2009 10:18:50 David Beacham wrote:
> > >       
> > > > Johan Hake wrote:
> > > >         
> > > > > On Wednesday 16 December 2009 09:28:21 David Beacham wrote:
> > > > >           
> > > > > > Hi,
> > > > > >
> > > > > > I'm not sure if it's my relative inexperience with python, but I can't
> > > > > > find the coordinates x in data, when overloading eval_data in
> > > > > > Expression. I'm guessing from doxygen/pydoc that they should be
> > > > > > available?
> > > > > >             
> > > > > Have you tried:
> > > > >
> > > > >   x = data.x()
> > > > >           
> > > > No, I don't seem to have the Data.x() method either:
> > > >
> > > > (Pdb) p data.x()
> > > > *** AttributeError: AttributeError("'Data' object has no attribute
> > > > 'x'",)
> > > >
> > > > although everything else from the cpp side is showing up and is useable:
> > > >
> > > > (Pdb) p dir(data)
> > > > ['__class__', '__delattr__', '__dict__', '__doc__', '__format__',
> > > > '__getattribute__', '__hash__', '__init__', '__module__', '__new__',
> > > > '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__',
> > > > '__str__', '__subclasshook__', '__swig_destroy__', '__weakref__',
> > > > 'cell', 'clear', 'facet', 'geometric_dimension', 'normal', 'on_facet',
> > > > 'set', 'this', 'thisown', 'ufc_cell']
> > > >
> > > > FWIW, I can get Data.x to work in cpp.
> > > >         
> > > This should be fixed now.
> > >
> > > Johan
> > >       
> > Thanks for this, I can now see data.x, but it isn't returning the
> > correct information:
> >
> > (Pdb) !z = data.x()
> > (Pdb) z
> > array([], dtype=float64)
> > (Pdb) z.shape
> > (0,)
> >     
>
> David!
>
> Can you run the unit test of function and see if it pass? At line 77 we test 
> subclassing of Expression using the eval_data interface. The test pass on my 
> computer.
>
> If it pass, can you hand a minimal example that break, either just attach one 
> or tweak the unit test.
>
> Johan
>   
Thanks for pointing out the unittests. I've worked out my problem was 
related to directly plotting my expression but interpolating to a 
function space does the correct things with data.x():

class MyExp(Expression):
   def eval_data(self, value, data):
       x = data.x()
       print x
       value[0] = x[0]

mesh = UnitSquare(10,10)
V = FunctionSpace(mesh, "CG", 2)

my_exp = MyExp()

1. If I define an expression and then interpolate that to a function 
everything works correctly, and data.x() gives the correct results.
# this does the right thing: print x -> [x   y]

f = Function(V)
f.interpolate(my_exp)
plot(f, interactive=True)

2. If I try to plot my expression directly, then data.x() doesn't return 
anything.
#print x -> []
plot(my_exp, mesh=mesh, interactive=True)

David

>   
> > David
> >
> >     
> > > > > We needed to make the x attribute a method returning the x array in
> > > > > Python.
> > > > >
> > > > > Johan
> > > > >
> > > > >           
> > > > > > David
> > > > > >
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