This ticket tracks the work contained in Pull Request #1291.

We added these expressions:

'$cossim', '$chi2', '$euclidean', '$squared_euclidean', '$manhattan'

Which allow us to compare long vectors (image features) stored as arrays or BSON.
It is useful to find the most similar images in a dataset. The usage is the following:

db.test_speed.aggregate([
    {   
        '$project':
        {
            'id': '$id',
            "other_id": '$other_id',
            'distance': {'$cossim': [vector, '$vector']},
        },
    },
    {"$sort": {"distance": -1}},
    {"$limit": 20}
])

In addition implementations using avx2 and avx512 are included in this pull request.