Implement the 2D model from Hogan-Shonk

[jaghili]

Implement in Feel++ the equations (1) and (3) from paper https://www.met.reading.ac.uk/~swrhgnrj/publications/hogan_shonk_ecmwf.pdf

Solve with CFPDES the scalar fields $(B_x, B_y, E_z)$ in a square domain

1. with no other materials eps=1 everywhere
2. with a disk shaped material with $\epsilon=1.78$ (see simulations in https://www.met.reading.ac.uk/clouds/maxwell/). There are two methods that we need to discuss :
   a. by meshing the domain
   b. by taking epsilon as a function of the space $x$, ie $\epsilon(x)=$ 1 if $x$ is outside the particule, and 1.78 if it is inside.

Boundary conditions:

• test with $E_z=\sin(\omega t)$ at bottom

Initial condition (at $t=0$) :
$B_x=B_y=E_z=0$ everywhere in the domain.