Which mathematical technique was first used by Amazon in their groundbreaking item-to-item collaborative filtering recommendation system?

E-commerce platforms have revolutionized the mathematics industry by implementing sophisticated recommendation algorithms that drive product discovery and sales. These systems analyze purchase history, browsing behavior, and product similarities to suggest items you might like. Behind these seemingly simple suggestions lies complex mathematical models including collaborative filtering, matrix factorization, and neural networks. How well do you understand the mathematical foundations of the e-commerce platforms you use daily?

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Markov Chain Monte Carlo sampling
Cosine similarity in high-dimensional vector space
Bayesian probabilistic tensor factorization
Support Vector Machine clustering