Wrong relativistic wavelength expression found

[KylinGuo]

The relativistic wavelength expression given at the following page

https://ubermag.github.io/api/_autosummary/mag2exp.ltem.relativistic_wavelength.html#mag2exp.ltem.relativistic_wavelength

is wrong. See the image below.

Please correct it. One could find the details at the following page

https://zhuanlan.zhihu.com/p/629008312

It was given in Chinese but the result is quiet straightforward.

[samjrholt]

@KylinGuo Thank you for pointing this out. I can confirm that whilst the code is correct the expression given in the API documentation has an additional $2 m0 e U$ term. This has now been updated on the master branch of mag2exp and will appear on the website when we next update it.