• https://en.wikipedia.org/wiki/Haversine_formula
• https://en.wikipedia.org/wiki/Great_circle - has a picture of what is meant by the great circle in the context of a sphere.
• https://en.wikipedia.org/wiki/Versine#Haversine - has a picture that shows how trigonometric functions can be constructed geometrically using unit circle. Contains a table of derivative and integral formulas for various types of versines.
• http://rosettacode.org/wiki/Haversine_formula#Python - gives barebones python code. In practice, we are probably better off using scikit-learn functions?
• https://stackoverflow.com/questions/34557898/pairwise-haversine-distance-calculation - In practice, we are probably better off using scikit-learn functions. But the discussion, sample code here is probably useful?

• The sklearn.metrics.pairwise.haversine_distances function was added in 0.21.0
• The 0.21.0 was released on 2019-05

Ref:-

• https://scikit-learn.org/dev/whats_new/v0.21.html#id16 - changelog entry
• https://scikit-learn.org/dev/whats_new/v0.21.html#version-0-21-0 - shows the release date

Code references:-

• https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/metrics/tests/test_pairwise.py → test_haversine_distances() shows a sample call. This function also contains a slower implementation. Afterwards, compare the timings of the native scikit-learn function and its slower implementation.
• https://github.com/scikit-learn/scikit-learn/blob/0.23.2/sklearn/metrics/pairwise.py → haversine_distances() shows the implementation.

Documentation:-

• https://scikit-learn.org/stable/modules/generated/sklearn.metrics.pairwise.haversine_distances.html