My initial thought was that this couldn't be too hard since the only difference is the basis functions being piecewise constant instead of linear, all the other stuff like dofmaps, sparsity patterns (?) and so on are identical as Martin points out. I have little to no knowledge of the general FEniCS implementation so this may be harder then I think, but it doesn't sound too complicated.
Joakim -- Joakim Bø Prosjektleder ENT3R UiO Tlf.: 915 24 326 http://www.ENT3R.no/OSLO ________________________________ From: Anders Logg <[email protected]> Sent: 20 April 2015 18:00 To: Martin Sandve Alnæs; Joakim Bø Cc: Jan Blechta; [email protected] Subject: Re: [FEniCS] Implement a new finite element type for testing purposes? Yes, it might actually be that simple: The elements would be standard P1 elements with the only difference that the value of the basis functions are always one (each triangle has 3 basis function and each is = 1) and all derivatives are zero. Might be possible to "hack" by modifying _create_fiat_element(ufl_element) in ffc/fiatinterface.py. -- Anders mån 20 apr. 2015 kl 17:44 skrev Martin Sandve Alnæs <[email protected]<mailto:[email protected]>>: Doesn't sound that hard. Basically dofmaps like CG1 elements with basis functions replaced by 1.0 on the entire support? On 20 April 2015 at 15:37, Joakim Bø <[email protected]<mailto:[email protected]>> wrote: Thanks for answering! Anders got it right, discontinous and overlapping basis functions with the same global support as P1 tent functions. Sorry to hear that it would be hard to implement, but it came as no surprise... Thanks anyway! Joakim -- Joakim Bø Prosjektleder ENT3R UiO Tlf.: 915 24 326 http://www.ENT3R.no/OSLO ________________________________ From: Anders Logg <[email protected]<mailto:[email protected]>> Sent: 20 April 2015 13:46 To: Andrew McRae; Jan Blechta Cc: Joakim Bø; [email protected]<mailto:[email protected]> Subject: Re: [FEniCS] Implement a new finite element type for testing purposes? If I understand correctly, you want discontinuous and overlapping basis functions with the same global support as the P1 tent functions. Unless you find a clever trick for how to treat this (perhaps via some linear algebra using P0 elements in combination with some suitable constraints), this looks difficult to implement in FEniCS. We assume each element is defined locally on triangles/tetrahedra. -- Anders mån 20 apr. 2015 kl 13:14 skrev Andrew McRae <[email protected]<mailto:[email protected]>>: I interpret it as a DG0, but where nodes are associated with vertices. Related to mass-lumping, I guess. On 20 April 2015 at 12:07, Jan Blechta <[email protected]<mailto:[email protected]>> wrote: On Fri, 17 Apr 2015 10:21:33 +0000 Joakim Bø <[email protected]<mailto:[email protected]>> wrote: > Hi! > > > I am in need of a new type of basis function for testing purposes. It > is much similar to the basis functions of the Taylor-Hood P1 element, > the difference is that the functions are piecewise constant equal to > 1 in this "local domain" (similar for 1D and 3D): > > > [http://www.fsz.bme.hu/~szirmay/radiosit/rad10.gif] > > > and zero in the rest of the domain. In general, phi_i = 1 for "local > domain of dof i", 0 else. If I understand your explanation correctly (it does not seem to match with the figure!), it is Discontinuous Lagrange element of degree 0, which is implemented. Jan > > > Would it be possible to implement this without too much work? Or > would it require a lot of effort? > > > Thanks! > > Joakim > > > -- > Joakim Bø > Prosjektleder ENT3R UiO > Tlf.: 915 24 326 > > http://www.ENT3R.no/OSLO _______________________________________________ fenics mailing list [email protected]<mailto:[email protected]> http://fenicsproject.org/mailman/listinfo/fenics _______________________________________________ fenics mailing list [email protected]<mailto:[email protected]> http://fenicsproject.org/mailman/listinfo/fenics
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