Lukas,

for solving the (ideal) MHD equations, I would like to implement two custom
shapesets:

By "shapeset" do you mean "set of shape functions"?


  * one for the flow part, completely discontinuous, scalar FE space, analogy
    to FE_DGQ, but based on Taylor expansion in the cell center

      o this should be the easy part, but I would like to ask how to go about
        it in deal.ii - I would like to implement at least linear and
        quadratic functions

Do you do the Taylor expansion in real space, or on the reference cell and then map to real space?

If the former, I think you will want to look at the implementation of the FE_DGP and FE_DGP_Monomial classes, of which at least one does something similar IIRC.


  * one for the magnetic field, a vector Hdiv space, analogy to
    FE_RaviartThomas, but in this case a space of divergence-free functions
    that satisfy div F = 0 within the reference cell
      o this I assume will be more difficult, but here I am only after linear
        functions

Again: on the reference cell or in real space?

If you work in real space, then in 2d there are 2x3 basis functions for the linear space (two vector components, each of which has the form a+bx+cy), of which you can eliminate one because of the divergence constraint, if I count correctly.

If you map from the reference cell, but require that div u = 0 pointwise in real space, then things may be more complicated.

Best
 Wolfgang

--
------------------------------------------------------------------------
Wolfgang Bangerth          email:                 [email protected]
                           www: http://www.math.colostate.edu/~bangerth/

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