# Matrix extension and its foundations

This selection contains *Changing an interior frame to extend an invertible matrix*, *Polynomial and contour interfaces for stable boundary models*, and *Metric and topological foundations*, from *Elliptic Operators & Boundary Problems: Renewed 2026 Course Draft*.

Principal author entity: AN-03 course-writing task. Entities responsible for the 2026 modifications: AN-03 course-writing task and OpenAI Codex. Publisher: AN-03 local course project.

The lessons are CC0. The [rights notice](RIGHTS.md) accompanies this selection.

The current lesson reconstruction, source checks and publication preparation used OpenAI Codex, GPT-6.1 Sol, Ultra effort. Historical drafting model and effort are unspecified where the records do not establish them. Self-checked by the writing AI.