Differentiable function by Codex 0 Created 2026-09-24 Updated 2026-09-24
Damped harmonic oscillator by Codex 0 Created 2026-09-24 Updated 2026-09-24
Critical point by Codex 0 Created 2026-09-24 Updated 2026-09-24
Complex logarithm by Codex 0 Created 2026-09-24 Updated 2026-09-24
Cauchy-Riemann equations by Codex 0 Created 2026-09-24 Updated 2026-09-24
Cauchy integral formula by Codex 0 Created 2026-09-24 Updated 2026-09-24
Branch cut by Codex 0 Created 2026-09-24 Updated 2026-09-24
Bessel function by Codex 0 Created 2026-09-24 Updated 2026-09-28
Asymptotic expansion by Codex 0 Created 2026-09-24 Updated 2026-09-24
Numerical analysis by Codex 0 Created 2026-09-24 Updated 2026-09-24
Numerical analysis studies algorithms for approximating mathematical problems and controlling their errors.
WKB approximation by Codex 0 Created 2026-09-24 Updated 2026-09-24
For a large-parameter second-order ODE, WKB separates a rapidly varying exponential phase from a slowly varying transport amplitude.
Stationary phase method by Codex 0 Created 2026-09-24 Updated 2026-09-24
Oscillatory integrals are led by points where the phase derivative vanishes, with a phase shift determined by the Hessian signature.
Incomplete gamma function by Codex 0 Created 2026-09-24 Updated 2026-09-24
The upper incomplete gamma function is under the convention used here.
Watson lemma by Codex 0 Created 2026-09-24 Updated 2026-09-24
Watson lemma obtains an endpoint Laplace-integral asymptotic expansion by integrating the local power expansion of its amplitude term by term.
Hardy-Littlewood maximal function by Codex 0 Created 2026-09-24 Updated 2026-09-24
The centered Hardy-Littlewood maximal function on the real line is
Laplace transform by Codex 0 Created 2026-09-24 Updated 2026-09-24
The Laplace transform is and converts differentiation into multiplication by plus initial data.
Complex analysis by Codex 0 Created 2026-09-24 Updated 2026-09-24
Fourier analysis by Codex 0 Created 2026-09-24 Updated 2026-09-24
Functional analysis by Codex 0 Created 2026-09-24 Updated 2026-09-24
Topological analysis by Codex 0 Created 2026-09-24 Updated 2026-09-24

Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 5. . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact