Posterior and MAP Derivation for Categorical Distribution in TensorFlow Probability

This note provides a complete derivation of the posterior distribution and the Maximum A Posteriori (MAP) estimate for a Categorical distribution with a Dirichlet prior, including an example implementation in TensorFlow Probability.

Machine Learning & Simulation1.4K views39:20

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We put a Dirichlet prior on the Categorical's parameter vector. Now let's derive the Posterior and the Maximum A Posteriori Estimate (MAP). Here are the notes: https://raw.githubusercontent.com/Ceyron/machine-learning-and-simulation/main/english/essential_pmf_pdf/categorical_posterior_and_map.pdf The Dirichlet Distribution is the conjugate prior to the Categorical. We use this fact to intuitively derive the posterior and its mode, the Maximum A Posterior (MAP) Estimate. ------- 📝 : Check out the GitHub Repository of the channel, where I upload all the handwritten notes and source-code files (contributions are very welcome): https://github.com/Ceyron/machine-learning-and-simulation 📢 : Follow me on LinkedIn or Twitter for updates on the channel and other cool Machine Learning & Simulation stuff: https://www.linkedin.com/in/felix-koehler and https://twitter.com/felix_m_koehler 💸 : If you want to support my work on the channel, you can become a Patreon here: https://www.patreon.com/MLsim ------- Timestamps: 00:00 Introduction 00:50 Motivation 01:17 Repetition: The Categorical 01:56 Directed Graphical Model 03:32 The joint distribution 05:51 Bayes' Rules 06:35 Proportional Posterior 08:02 Plugging in Dirichlet & Categorical 09:09 Simplifying Proportional Posterior 13:09 Why Dirichlet is conjugate prior 13:49 "Posterior Likelihood" 14:06 Two Paths 14:52 Deriving the Posterior 17:39 MAP: Setup 18:12 MAP: Log-Posterior Likelihood 19:15 MAP: Lagrange Multiplier 20:51 MAP: Maximization 28:12 Discussing the MAP 19:19 MAP for the One-Hot Categorical 30:18 TFP: Create a dataset 32:00 TFP: n observations per state 32:33 TFP: Calculating the MLE 32:52 TFP: Calculating the MAP 34:39 TFP: MLE/MAP for corrupt dataset 37:10 TFP: Posterior Distributions 38:47 Outro

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Apr 21, 2021

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