Make test case to compare Period04 results to Pyriod (and other packages)

[hippke]

Fantastic package!

Part of the variable star community considers Period04 as the "ground truth" and suspects software with even slightly different results to contain bugs. I'm not sure if that is wise, but what do you think about a set of test cases? We could compare the FFT frequencies calculated from various packages, such as:

• astropy
• scipy
• pyriod
• period04
• ?

[keatonb]

Thanks, I agree that this is a good idea. The results should certainly agree. The analysis in the example notebook has been compared to other pipelines preferred by various members of the TASC Working Group 8.2 and shows excellent agreement. Thanks for opening the issue.