Besides the number of PML cells, the resistivity boundaries, permittivity and the function used to compute the resistivity profile in the PML are now arguments for the SolverFIT3D

To make the init clearer, the PML parameters are given default values within the initialization. To customize the values for PML resistivity ans eps, user can access the attributes and re-execute fill_pml_sigmas to update the PML cells.

This first attempt uses the properties of the central cell of the layer adjacent to the PML, assuming the beam is centered

Relaxation times were incorrect when sigma=0 in the simulation space, as the whole PML had sigma=0

… cases other than vacuum

The sigma for the PML layers is now the sigma of the previous non-PML layer + the function of resistivity. This function starts from the sigma value of the layer if it is non zero, or from a low sigma value

This is to improve field absorption, in particular if we have vacuum. One might need more layers of PML then

…ion time computation

This still needs to be worked out, as there are some divergence in computations