fixed kernel transfer function

[David-Morales-Norato]

This pull request addresses the error reported in Issue #97 concerning the incorrect kernel equation in the odak.learn.wave.classical.get_transfer_function_fresnel_kernel function.

[kaanaksit]

Hi David,

Thank you for bringing this issue to my attention and showing interest in my work.

Both equations are in fact providing a similar response in the Fresnel region, and they are practically both correct. We use these kernels mostly in the Fresnel region. I am happy to merge your request. But in case you decide to contribute this project, a style related thing that I would encourage you to follow:

Please add space between mathematical operations. For instance, from your code:

H = torch.exp(1j*distance* (k- torch.pi *wavelength*(FX**2 + FY**2)))

Should be:

H = torch.exp(1j * distance * (k - torch.pi * wavelength * (FX ** 2 + FY ** 2)))

I have also included your name to THANKS.txt. I appreciate it if you could have a separate pull request for updating CITATION.cff in the root directory. Please make sure to add your orcid ID. Btw, you can always approach me for scientificc collaborations related to holography. My email is kaanaksit@kaanaksit.com.

Thanks,

Best regards,
Kaan