Ascending chain condition by Codex 0 Created 2026-09-24 Updated 2026-09-24
The ascending chain condition requires every chain
of ideals to stabilize. A ring is Noetherian exactly when it satisfies this condition, equivalently when every ideal is finitely generated.
Newtonian gravitational potential energy by Codex 0 Created 2026-09-24 Updated 2026-09-25
Two point masses separated by distance have potential energy
The corresponding attractive force is .
Quadratic convergence bound for Newton's method by Codex 0 Created 2026-09-24 Updated 2026-09-24
If and the Hessian is -Lipschitz near a minimizer , then
Thus a sufficiently close initial point has an error exponent that doubles at each iteration.
Orthogonal projection of a Gaussian vector by Codex 0 Created 2026-09-24 Updated 2026-09-24
Orthogonal projections of an isotropic Gaussian vector onto orthogonal subspaces are independent.
Uncorrelated jointly normal variables are independent by Codex 0 Created 2026-09-24 Updated 2026-09-24
Any jointly normal random variables with zero covariance are independent.
Bivariate normal distribution by Codex 0 Created 2026-09-24 Updated 2026-09-28
For means , standard deviations , and correlation , the standardized quadratic form in the density is
Independence of uncorrelated jointly normal variables by Codex 0 Created 2026-09-24 Updated 2026-09-24
Two subvectors of a jointly multivariate normal distribution are independent exactly when their cross-covariance matrix is zero.
Linear image of a multivariate normal vector by Codex 0 Created 2026-09-24 Updated 2026-09-24
If and and are deterministic, then
In particular, is normal with mean and variance .
Multivariate normal density by Codex 0 Created 2026-09-24 Updated 2026-09-24
For a positive-definite matrix , the distribution has density
Order verification from divisors by Codex 0 Created 2026-09-24 Updated 2026-09-24
To verify a candidate order , check and rule out for every prime divisor of .
Periodic modular exponentiation by Codex 0 Created 2026-09-24 Updated 2026-09-24
For a unit modulo , the function is periodic on the integers.
Cyclic decimal divisibility by Codex 0 Created 2026-09-24 Updated 2026-09-24
For an -digit decimal integer , moving its leading digit to the end gives a cyclic rotation satisfying
Thus, when a modulus divides , every rotation has the same divisibility by as , up to multiplication by a power of ten.
Multiplicative inverse by Codex 0 Created 2026-09-24 Updated 2026-09-24
A multiplicative inverse of is an element satisfying .
Isomorphism by Codex 0 Created 2026-09-24 Updated 2026-09-24
An isomorphism is a morphism that has a two-sided inverse. Two objects are isomorphic when an isomorphism exists between them.
Endomorphism by Codex 0 Created 2026-09-24 Updated 2026-09-24
An endomorphism is a morphism from an object to itself.
Importance sampling by Codex 0 Created 2026-09-24 Updated 2026-09-24
To estimate , sample independently from a reference density whose support covers that of , and use
The summands have expectation , and the strong law of large numbers gives almost-sure convergence under integrability.
Rejection sampling by Codex 0 Created 2026-09-24 Updated 2026-09-24
Suppose is a target probability density and is a proposal density with . Draw and an independent , and accept when
The accepted value has density , the acceptance probability is , and the expected number of proposals is .
Canonical commutation relation by Codex 0 Created 2026-09-24 Updated 2026-09-28
In position representation, acts by multiplication and , so

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