Add Octave Functions for a Multi Term Debye approximation of the Djordjevic-Sarkar model

[toammann]

Hello,
This pull request introduces two Octave functions for creating a Multi-Term Debye approximation of the Djordjevic-Sarkar model:

CalcDjordjevicSarkarApprox.m
This function computes the wide band Djordjevic-Sarkar model based on the original publication [1], using a single frequency, loss tangent, and relative permittivity as input. It then fits a multi-term Debye model to the result. The function includes plots (in both log and linear scale) to help visualize and review the model behavior.

AddDjordjevicSarkarMaterial.m
This function wraps CalcDjordjevicSarkarApprox and adds the resulting Debye material to the CSX structure for use within openEMS.

Please find additional information in the GitHub Discussions thread.

Documentation and a tutorial are planned.

Regards,
Tobias

Reference:
[1] Djordjevic, Antonije R., et al. "Wideband frequency-domain characterization of FR-4 and time-domain causality." IEEE Transactions on electromagnetic compatibility 43.4 (2001): 662-667.

[biergaizi]

Minor formatting nitpicking. We're now auto-generating Octave function documentation, which will appear on the official website in the future. Thus, all Octave docstrings must be correctly formatted in the Markdown format. This requires you to change the docstrings using this PR as an example.

It boils down to basically two things:

1. Use - before each argument, so it gets formatted as a Markdown list.
2. Add one blank line and 4 spaces to form a code block in the code example.

[toammann]

Hey biergaizi,
thanks for checking. I made the requested changes. Hopefully it fits now the convention.
Regards,
Tobias

[thliebig]

I think the resulting doc looks good now. The created files are just not linked to anywhere just yet...