dolfin team mailing list archive

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

Marie Rognes wrote:
> I have a slightly interesting issue, possibly with interpolate:
>
> Say I have a RT_0 function u. I want to interpolate this function onto a 
> DG_1 function Pi_u.
> Since RT_0 \subset DG_1, I would expect to get the same function. This 
> does not seem
> to be the case at the moment.

Need to be careful interpolating in discontinuous spaces because you 
will pick up the 'last' evaluated term, i.e. you can't be sure which on 
side the function will be evaluated on. This could be the issue. Have a 
look inside the interpolate functions in Function.cpp.

Garth

> ||u||_0 =  1.12846688033
> ||Pi_u||_0 =  1.2624381173
>
> being the output of:
>
> from dolfin import *
>
> mesh = UnitSquare(2, 2)
>
> V_h = FunctionSpace(mesh, "RT", 0)
> u = Function(V_h, ("pow(x[0],2)", "1.0"))
> u.interpolate()
> print "||u||_0 = ", norm(u)
>
> W_h = VectorFunctionSpace(mesh, "DG", 1)
> Pi_u = Function(W_h)
> Pi_u.interpolate(u)
> print "||Pi_u||_0 = ", norm(Pi_u)
>
>
> (Tested both using tensor and quadrature representation.
> Tensor and quad differ somewhat for the norm(u).
> Is the quadrature default to integrate RTs using
> "too low" a quadrature rule still?)
>
>
>
> --
> Marie
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