Hello all,

This is a follow up discussion to the Jean-Paul answer to the question "Is 
the approach for the electrostatic Bi-linear form correct?". The question 
(and answer) can be found at the following link:

https://groups.google.com/forum/#!topic/dealii/i8P4JTwm7kQ

In short, I am modeling the maxwell equations for the electric field and 
voltage scalar field. The equations that I am using are displayed below:

div(*E*) = rho / epsilon where epsilon = epsilon_{0} * epsilon_{r} and rho 
is the charge density of the material.

-grad(V) = *E*

Using Dr. Bangerth's recommendation, I am solving for the scalar voltage 
field first then taking the gradient of my solution using the 
DataPostprocessorVector class. This has worked extremely well in my test 
program. For more information on that, see this post: 
https://groups.google.com/forum/#!topic/dealii/XIiPyMh0Jz4

However, now that I am actually coding the solver of the simulation, I will 
need to expand on my test simulation to include modeling anisotropic 
materials.

When the material is anisotropic, the epsilon value (the permittivity) of 
the material is represented by a tensor. To make things slightly 
simplified, I am only running 2D simulations.

I am attempting to determine the best method on modeling these types of 
materials. One approach that I have considered is to still solve for the 
voltage scalar field. If I go with this approach, then I will end up 
simulating a Possion equation where f = rho / epsilon and epsilon is a 
tensor. My concern for this direction would be that the Laplacian operator 
results in a scalar value. So I am not sure how I would handle the tensor 
on the RHS. Unless Deal.II has some sort of provision for this.

I have also been kicking around the idea of solving for the displacement 
vector *D*(i)= epsilon(i)(j) * *E *by substituting this equation into one 
of the equations above. Or at the very least, to use this equation as a 
constitutive relation to the equations above.

A third approach that I haven't quite explored very much is solving for the 
polarization of the material. But I am not sure if this is a practical 
approach since I could unnecessarily complicate the problem.

I wanted to post a discussion on this form to discuss what the best 
direction I should take to model anisotropic materials in Deal.ii? I have 
been looking at 3 different approaches and I would like to discuss which 
one of these 3 directions is the better. Or if there might be others that I 
have not considered yet.

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