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Chris Piech, Stanford CS109 (2023)

Probability for
Computer Scientists

The complete Stanford CS109 course reader, rebuilt as interactive lessons. From counting to machine learning, with simulations at every step.

15
Chapters
56
Simulations
150
Quizzes
Part 1: Core Probability
Chapter 1

Counting & Combinatorics

Step rule, permutations, combinations, binomial coefficients, stars & bars, multinomials.

Chapter 2

Probability Basics

Empirical definition, sample spaces, equally likely outcomes, complement, inclusion-exclusion.

Chapter 3

Conditional Probability & Bayes

Conditional probability, chain rule, independence, law of total probability, Bayes’ theorem.

Chapter 4

Applications of Core Probability

Many coin flips, Enigma machine, birthday paradox, random shuffles, Gini impurity.

Part 2: Random Variables
Chapter 5

Random Variables & PMFs

Definition, PMF, CDF, functions of RVs, indicator variables.

Chapter 6

Expectation & Variance

E[X], linearity, LOTUS, variance, standard deviation, properties.

Chapter 7

Discrete Distributions

Bernoulli, Binomial, Poisson, Geometric, Negative Binomial, Categorical.

Chapter 8

Continuous Distributions

PDF, CDF, Uniform, Exponential, Normal, Z-scores, binomial approximation.

Part 3: Probabilistic Models
Chapter 9

Joint Distributions

Joint PMF/PDF, marginalization, multinomial, covariance, correlation.

Chapter 10

Inference & Bayesian Networks

Bayes for RVs, MAP/MLE preview, Bayesian networks, conditional independence.

Chapter 11

General Inference

Inference framework, prior/posterior, likelihood, fairness in AI.

Part 4: Uncertainty Theory
Chapter 12

Beta Distribution & CLT

Beta as conjugate prior, convolution, Central Limit Theorem, proof sketch.

Chapter 13

Sampling & Bootstrapping

Random sampling, bootstrap CIs, entropy, KL divergence, information theory.

Part 5: Machine Learning
Chapter 14

Parameter Estimation

Likelihood, log-likelihood, MLE for Bernoulli/Normal, MAP, prior influence.

Chapter 15

Machine Learning

Naive Bayes, logistic regression, sigmoid, cross-entropy, gradient descent, diffusion.