Lecture 15 of ML Foundations tackles model selection. Selecting by E_in overfits, and selecting by E_test is cheating. The compromise is to carve a validation set out of the training data, select by E_val, then retrain on all the data. The validation size K is a dilemma, with K = N/5 as the rule of thumb. Leave-one-out is almost unbiased but expensive and unstable, so in practice you use 5-fold or 10-fold. Lecture 16 closes with three principles, Occam's razor, sampling bias, and data snooping, and a 'Power of Three' recap: three related fields, three bounds, three linear models, three tools. Practice problems are in Fall 2024 HW5.
Ask AI finding a post does not mean the UI should display it as a source. An answer must pass deterministic Markdown and URL validation, then the Critic's relevance, intent, and grounding checks; if either gate fails, source cards are withheld.
Writer sees the first 8 candidates for a factual query or 12 for a recommendation by default. Citations must use an exact `source_url` from that set, and weak or empty retrieval triggers an instruction to abstain rather than fill gaps from model knowledge.
Zod's 224M weekly downloads (checked August 2026) put it far beyond 'form validation library': API boundaries, environment variables, route search params, LLM tool schemas and structured output all run on the same schemas. The core mechanism is one definition, two payoffs — runtime validation and static types derived from a single source. Zod 4 (on npm July 2025) is faster, slimmer, and easier on tsc.
OpenClaw validates config strictly — one unknown key, a wrong type, or an invalid value and the Gateway refuses to start. It keeps a last-known-good copy, but neither startup nor hot reload restores it automatically; only doctor --fix does.
React Hook Form handles form performance, Zod defines the validation schema — together they eliminate nearly all form boilerplate. Share a single Zod schema across a monorepo and you get one source of truth for both frontend and backend validation.
TypeScript types only exist at compile time — they vanish at runtime. Zod lets you validate external data at runtime while inferring TypeScript types from the same schema. One definition, two jobs done.