Neural Networks: Zero to Hero - Andrej Karpathy vs PostHog

Delivers structured video lectures that progressively build neural network understanding from mathematical foundations through implementation, using a pedagogical approach that alternates between conceptual explanation and live coding demonstrations. Each lecture combines whiteboard derivations of backpropagation, gradient descent, and activation functions with real-time implementation in Python/PyTorch, enabling learners to see theory-to-code mapping directly.

Unique: Uses a 'zero to hero' pedagogical progression where each lecture builds incrementally from mathematical first principles through complete working implementations, with Karpathy personally demonstrating live coding alongside whiteboard derivations — creating tight coupling between theory and practice that most courses separate

vs alternatives: More rigorous mathematical foundation and live-coding demonstrations than fast.ai, more accessible than Stanford CS231N lectures, and more implementation-focused than pure theory courses like Andrew Ng's Coursera specialization

Provides a complete walkthrough of building a minimal automatic differentiation engine (micrograd) from scratch in Python, demonstrating how computational graphs track operations, how backpropagation traverses these graphs to compute gradients, and how gradient descent updates parameters. The implementation uses a directed acyclic graph (DAG) structure where each operation node stores references to its inputs and a backward function, enabling reverse-mode autodiff.

Unique: Implements a minimal but complete autodiff engine that reveals the core mechanism (DAG-based reverse-mode differentiation with closure-based backward functions) in ~100 lines of readable Python, making the abstraction transparent rather than hiding it in compiled code like PyTorch does

vs alternatives: More transparent and educational than studying PyTorch's C++ autograd implementation, more complete than toy examples in blog posts, and demonstrates the actual architectural pattern used in production frameworks

Introduces convolutional neural networks by explaining how convolution operations extract spatial features, how pooling reduces dimensionality, and how stacking these layers builds hierarchical feature representations. The implementation shows how to implement convolution as a sliding window operation, how to compute gradients through convolution, and how to design CNN architectures for image tasks.

Unique: Derives convolution as a sliding window operation that shares weights across spatial positions, shows how this enables translation invariance and parameter efficiency, and implements both forward and backward passes to reveal how gradients flow through convolution

vs alternatives: More thorough than framework documentation, more practical than pure signal processing theory, and includes implementation details that clarify how convolution differs from fully-connected layers

Explains recurrent neural networks by showing how they maintain hidden state across time steps, how unrolling creates a computation graph through time, and how backpropagation through time (BPTT) computes gradients. Demonstrates the RNN equations (hidden state update, output computation) and discusses challenges like vanishing/exploding gradients that arise from long sequences.

Unique: Shows how RNNs maintain hidden state across time steps through recurrence, derives the unrolled computation graph through time, and explains backpropagation through time (BPTT) as standard backprop on the unrolled graph, revealing why gradients vanish/explode in long sequences

vs alternatives: More thorough than framework documentation, more accessible than academic papers on RNNs, and includes clear visualization of unrolled computation graphs

Walks through building a complete training loop that orchestrates forward passes, loss computation, backward passes, and parameter updates, demonstrating how these components interact in sequence. The implementation shows explicit gradient zeroing, loss calculation, backpropagation invocation, and optimizer steps, revealing the control flow and state management required for iterative training.

Unique: Explicitly shows the imperative control flow of training (forward → loss → backward → step → zero_grad) with clear state transitions, rather than abstracting it away in high-level APIs, making the mechanical process visible and modifiable

vs alternatives: More explicit and debuggable than PyTorch Lightning or Hugging Face Trainer abstractions, more practical than theoretical ML textbooks, and shows the actual code patterns used in production systems

Demonstrates how to design and implement fully-connected neural networks with multiple hidden layers, including decisions about layer sizes, activation functions, and weight initialization. The implementation shows how to compose layers sequentially, how activation functions introduce non-linearity, and how network depth affects expressiveness and training dynamics.

Unique: Builds MLPs incrementally from single neurons to multi-layer networks, explicitly showing how each layer adds non-linear transformation capacity and how the composition creates universal approximators, with clear visualization of how depth enables learning complex functions

vs alternatives: More pedagogically structured than PyTorch documentation, more practical than theoretical proofs of universal approximation, and shows actual implementation patterns rather than just conceptual diagrams

Provides a complete mathematical derivation of the backpropagation algorithm using the chain rule, showing how gradients flow backward through a network from loss to parameters. The implementation demonstrates both the mathematical formulation (partial derivatives, Jacobians) and the computational implementation (storing intermediate activations, computing gradients layer-by-layer), revealing how the algorithm achieves efficiency through dynamic programming.

Unique: Derives backpropagation from first principles using the chain rule, then shows the computational implementation that makes it efficient (storing activations, computing gradients in reverse topological order), making the connection between mathematical theory and practical algorithm explicit

vs alternatives: More rigorous mathematical treatment than most tutorials, more accessible than academic papers, and includes working code alongside derivations unlike pure theory courses

Analyzes different activation functions (ReLU, sigmoid, tanh, etc.) by examining their mathematical properties, derivatives, and effects on network training. The analysis includes visualization of activation curves, gradient flow properties, and empirical comparison of how different activations affect convergence speed and final accuracy on benchmark problems.

Unique: Combines mathematical analysis (derivative properties, gradient flow characteristics) with empirical visualization and training experiments, showing both why certain activations work better theoretically and demonstrating the practical effects on convergence

vs alternatives: More comprehensive than activation function documentation in frameworks, more practical than pure mathematical analysis, and includes empirical comparisons that theory alone cannot provide

PostHog/posthog | DeepWiki Loading... Index your code with Devin DeepWiki DeepWiki PostHog/posthog Index your code with Devin Edit Wiki Share Loading... Last indexed: 28 May 2026 ( 4a5e38 ) Overview Monorepo Structure and Build System Frontend Workspace and Product Packages Python Dependencies and Configuration CI/CD Pipeline Schema and Type System Cross-Language Schema Synchronization Query Schema Definitions Database Migrations Data Storage and Ingestion ClickHouse Architecture Kafka to ClickHouse Pipeline PostgreSQL and Database Pools Query Log Archive System Event Ingestion Pipeline (Node.js) Backend Services Django Middleware System Feature Flags Service (Rust) API Layer and Authentication Rust Microservices LLM Gateway Service Agentic Provisioning and OAuth Max AI Assistant Architecture and Agent Modes Query Execution and Streaming Frontend Integration MCP Server Tasks (AI Coding Agent) Feature Flags System Feature Flag Management API Flag Evaluation and Dependencies Frontend Interface Product Features Logs Viewer Session Recordings Insights and Analytics Surveys and Scheduled Changes Experiments (A/B Testing) Web Analytics Error Tracking LLM Analytics Frontend Architecture Kea State Management Product Module System Build System and Tooling Testing and Quality Test Infrastructure Backend and Rust Tests Frontend and E2E Tests Data Platform and Workf

Monorepo Structure and Build System | PostHog/posthog | DeepWiki Loading... Index your code with Devin DeepWiki DeepWiki PostHog/posthog Index your code with Devin Edit Wiki Share Loading... Last indexed: 28 May 2026 ( 4a5e38 ) Overview Monorepo Structure and Build System Frontend Workspace and Product Packages Python Dependencies and Configuration CI/CD Pipeline Schema and Type System Cross-Language Schema Synchronization Query Schema Definitions Database Migrations Data Storage and Ingestion ClickHouse Architecture Kafka to ClickHouse Pipeline PostgreSQL and Database Pools Query Log Archive System Event Ingestion Pipeline (Node.js) Backend Services Django Middleware System Feature Flags Service (Rust) API Layer and Authentication Rust Microservices LLM Gateway Service Agentic Provisioning and OAuth Max AI Assistant Architecture and Agent Modes Query Execution and Streaming Frontend Integration MCP Server Tasks (AI Coding Agent) Feature Flags System Feature Flag Management API Flag Evaluation and Dependencies Frontend Interface Product Features Logs Viewer Session Recordings Insights and Analytics Surveys and Scheduled Changes Experiments (A/B Testing) Web Analytics Error Tracking LLM Analytics Frontend Architecture Kea State Management Product Module System Build System and Tooling Testing and Quality Test Infrastructure Backend and Rust Tests Frontend a

Schema and Type System | PostHog/posthog | DeepWiki Loading... Index your code with Devin DeepWiki DeepWiki PostHog/posthog Index your code with Devin Edit Wiki Share Loading... Last indexed: 28 May 2026 ( 4a5e38 ) Overview Monorepo Structure and Build System Frontend Workspace and Product Packages Python Dependencies and Configuration CI/CD Pipeline Schema and Type System Cross-Language Schema Synchronization Query Schema Definitions Database Migrations Data Storage and Ingestion ClickHouse Architecture Kafka to ClickHouse Pipeline PostgreSQL and Database Pools Query Log Archive System Event Ingestion Pipeline (Node.js) Backend Services Django Middleware System Feature Flags Service (Rust) API Layer and Authentication Rust Microservices LLM Gateway Service Agentic Provisioning and OAuth Max AI Assistant Architecture and Agent Modes Query Execution and Streaming Frontend Integration MCP Server Tasks (AI Coding Agent) Feature Flags System Feature Flag Management API Flag Evaluation and Dependencies Frontend Interface Product Features Logs Viewer Session Recordings Insights and Analytics Surveys and Scheduled Changes Experiments (A/B Testing) Web Analytics Error Tracking LLM Analytics Frontend Architecture Kea State Management Product Module System Build System and Tooling Testing and Quality Test Infrastructure Backend and Rust Tests Frontend and E2E Tests

PostHog/posthog | DeepWiki Loading... Index your code with Devin DeepWiki DeepWiki PostHog/posthog Index your code with Devin Edit Wiki Share Loading... Last indexed: 28 May 2026 ( 4a5e38 ) Overview Monorepo Structure and Build System Frontend Workspace and Product Packages Python Dependencies and Configuration CI/CD Pipeline Schema and Type System Cross-Language Schema Synchronization Query Schema Definitions Database Migrations Data Storage and Ingestion ClickHouse Architecture Kafka to ClickHouse Pipeline PostgreSQL and Database Pools Query Log Archive System Event Ingestion Pipeline (Node.js) Backend Services Django Middleware System Feature Flags Service (Rust) API Layer and Authentication Rust Microservices LLM Gateway Service Agentic Provisioning and OAuth Max AI Assistant Architecture and Agent Modes Query Execution and Streaming Frontend Integration MCP Server Tasks (AI Coding Agent) Feature Flags System Feature Flag Management API Flag Evaluation and Dependencies Frontend Interface Product Features Logs Viewer Session Recordings Insights and Analytics Surveys and Scheduled Ch