Fix typo in equation that computes interplanar angels

[EurusWei]

Summary

In the function get_interplnar_angle of module analysis/diffraction/tem.py, there are some typos about the angels and index.

Todo (if any)

N/A

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[mkhorton]

Thanks @EurusWei, much appreciated for catching this!

Can you suggest a good test for this function, e.g. a known input and output?

[coveralls]

Coverage decreased (-0.3%) to 46.594% when pulling 4c0cd65 on EurusWei:fix-equation into b566980 on materialsproject:master.

[EurusWei]

Thanks @EurusWei, much appreciated for catching this!

Can you suggest a good test for this function, e.g. a known input and output?

Hi Horton,

Has this catch been confirmed to be true? I am comparing the diffraction patterns (DPs) generated before and after the fix to those on the MaterialsProject website. I found the code before the fix generated DPs matched the MaterialsProject, instead of after the fix. Based on symmetry I am sure the equation should be fixed, but I don't know why the above phenomenon happens (not what I expected). Do you know how the MaterialsProject website generates their DPs?

[mkhorton]

Yes, I do -- the MP website uses the TEMCalculator exactly from pymatgen. At time of writing, this is pymatgen 2022.11.7.

We, at Materials Project, are likely switching to use functionality from py4DSTEM in future, and this is being worked on by @sezelt (and is looking really nice!) but right now, all functionality is unmodified from pymatgen.

[EurusWei]

I see, that makes sense. Since I don't have much background in this field, I cannot tell which DP is more accurate, before or after the fix. What about this: I will give you some examples that I find having discrepancies in DPs before and after the fix, together with my calculation results, and your group can help identify if this fix makes sense. After that you can either add some tests or directly merge the fix.