[dune-fem] coefficients of basefunction in the dg space

[Klaus Kaiser]

ah ok, thanks for this, I thought you were using other basis functions, then everything is clear ;-)

thanks

Klaus


Am 25.10.2012 um 13:24 schrieb Dedner, Andreas:

> Two remarks 
> If you are using a dg lagrange space then 1 0 0 0 would not be correct - locally your discrete function would would be the first lagrange hat function on the entity - 1at node with local number 0 whichever that is and zero at the other nodes. 
> If we are talking Legende dg space then your local dofs are correct I think. 
> 
> The local function can act like a vector for the local dof.  Is that not good enough for your application? 
> Greetings 
> Andreas 
> .
> 
> Klaus Kaiser <klaus.kaiser at rwth-aachen.de> wrote:
> Hi Tobias,
> 
> thanks for your fast answer. I have done the whole interpolation with LagrangeDiscontinuousGalerkinSpace and AdaptiveDiscreteFunction and set on every entity the dofs with
> 
> f.localFunction( *it )[j]=1;
> 
> where f is my AdaptiveDiscreteFunction. When I understood it right, then I iterate through every lagrange Point (DiscreteDGSpaceType::LagrangePointSetType) and set the value of the function at this point. So for example I got an constant Function (f(x)=1) and Polynomial Order 5, then on an entity the interpolation should look like this:
> 
> f_(x) = 1*phi_0(x)+0*phi_1(x)+0*phi_2(x)…
> 
> where phi_i is the i-the lagrange polynomial. With the function leakPointer(), I get an pointer on an array which gives me the functionvalues at the lagrange points. But I I think you misunderstood my question, I don't want to access the global DoF Vector, I want to access the coefficients of the basefunctions of the local functions. So in the example above I want to access an vector like this:
> 
> (1 0 0 0 0 0)
> 
> How do I get this vector? Or is this impossible?
> 
> Greetings & thanks
> 
> Klaus
> 
> 
> Am 25.10.2012 um 08:20 schrieb Tobias Malkmus:
> 
> > Hi Klaus
> > 
> > 
> > On 10/24/2012 06:48 PM, Klaus Kaiser wrote:
> >> Hi,
> >> 
> >> I have question concerning the dune-fem/dg part. I created an interpolation of a function in the discrete discontinuous galerkin space. This was done by setting the DoF Vector on every entity with the corresponding values of the function. Now I want to access the coefficients of the base functions, how do I do that? I searched a lot in the doxygen documentation, but didn't find a function, which gives me the values.
> >> 
> > This sounds to me like Lagrange Interpolation, for a DG Space a L2 projection would be the suitable interpolation method.
> > 
> > In Dune-Fem a discrete function is a combination of DofVector + DofMapper + LocalBasefunctions.
> > This allows you to generate localFunctions which are the local representation of a GridFunction / DiscreteFunction.
> > 
> > Some discreteFunction implementations allows you to access the DofVector as double*, eg. AdaptiveDiscreteFunction ( leakPointer() ).
> > 
> > Let me ask you where do you need the global Dof Vector?
> > 
> > Best Tobias
> > 
> >> Greetings and thanks for your help
> >> 
> >> Klaus
> >> 
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> >> 
> > 
> > 
> > -- 
> > Tobias Malkmus                 <tomalk at mathematik.uni-freiburg.de>
> > 
> > Mathematisches Institut               Tel: +49 (0) 761 203 5651
> > Abt. für Angewandte Mathematik        Universität Freiburg
> > Hermann-Herder-Str. 10
> > 79104 Freiburg
> > 
> 
> 
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