ffc team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

Anders Logg wrote:
> On Tue, Dec 23, 2008 at 07:31:06PM +0000, Garth N. Wells wrote:
> > I'm getting an error when trying something really simple with FFC. 
> > Compiling
> >
> >      U       = VectorElement("Lagrange", "triangle", 2)
> >      C       = FiniteElement("Lagrange", "triangle", 2)
> >      element = U + C
> >
> >      (v, c)  = Functions(element)
> >      v_h     = Function(U)
> >
> >      e = v - v_h
> >
> > leads to
> >
> > Traceback (most recent call last):
> >    File "/usr/bin/ffc", line 221, in <module>
> >      sys.exit(main(sys.argv[1:]))
> >    File "/usr/bin/ffc", line 104, in main
> >      execfile(script, {})
> >    File "Error.py", line 37, in <module>
> >      e = v - v_h
> >    File 
> > "/usr/lib/python2.5/site-packages/ffc/compiler/language/algebra.py", 
> > line 73, in __rsub__
> >      return Form(-self) + other
> >    File 
> > "/usr/lib/python2.5/site-packages/ffc/compiler/language/algebra.py", 
> > line 645, in __add__
> >      w1 = Form(other)
> >    File 
> > "/usr/lib/python2.5/site-packages/ffc/compiler/language/algebra.py", 
> > line 635, in __init__
> >      raise FormError, (other, "Unable to create Form from given 
> > expression.")
> > ffc.common.exceptions.FormError
> >
> >
> > If I do
> >
> >      U       = VectorElement("Lagrange", "triangle", 2)
> >      C       = FiniteElement("Lagrange", "triangle", 2)
> >      element = U + C
> >
> >      v       = Function(U)
> >      v_h     = Function(U)
> >
> >      e = v - v_h
> >
> > it works fine. Is this an obvious bug to fix?
> >
> > Garth
>
> It could presumably be fixed by modifying __rsub__ for the Element
> class in ffc/compiler/language/algebra.py to do something like
>
> def __rsub__(self, other):
>         "Operator: Element + Element (other - self)"
>         if isinstance(other, list):
>             return [other[i] - self[i] for i in range(len(other))]
>         return Form(-self) + other
>
> But maybe it's not worth the effort, considering we will soon throw
> away algebra.py and replace it by UFL?

Will this happen in January? Is UFL complete?

Garth

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