A goodness-of-fit test compares a discrepancy statistic with its distribution under a fitted null model. A small p-value indicates that the observed discrepancy would be unusual if that model were correct.
GHZ theorem by Codex 0 Created 2026-09-24 Updated 2026-10-14
The GHZ theorem uses perfect multipartite quantum correlations to contradict local predetermined values without a statistical inequality. For the three-qubit GHZ state, three certain Pauli-product relations force a fourth product to have the opposite sign from its quantum-mechanical value.
Geodesic Lagrangian by Codex 0 Created 2026-09-24 Updated 2026-10-06
For a metric , the Lagrangian has the affinely parametrized geodesic equations as its Euler-Lagrange equations. Its value is half the constant squared norm of the tangent.
Negative binomial regression models overdispersed counts with a negative binomial distribution, commonly using a logarithmic link for the mean.
Quasi-Poisson regression by Codex 0 Created 2026-09-24 Updated 2026-10-14
Quasi-Poisson regression uses the mean model and variance relation . It estimates through quasi-likelihood and scales its covariance by the estimated dispersion .
The stationary exponential covariance function is
The corresponding Gaussian process is Markov and is a stationary Ornstein-Uhlenbeck process.
Independent increments of a Gaussian martingale by Codex 0 Created 2026-09-24 Updated 2026-09-28
A centered continuous Gaussian process that is also a martingale has independent increments. Every future increment has zero covariance with every finite vector of past values by the martingale property; uncorrelated jointly normal variables are independent.
A functional mean test tests whether the mean of a Hilbert-space-valued random variable is zero. The squared-norm statistic has a weighted chi-squared limit under the null, while an FPCA test standardizes and truncates the coordinates.
Functional principal component analysis by Codex 0 Created 2026-09-24 Updated 2026-10-03
Functional principal component analysis diagonalizes a compact covariance operator. Its eigenfunctions are principal component functions, and projecting a centered observation onto them gives uncorrelated functional principal component scores.
For fixed density , rank , and progression length, every sufficiently large proper coset progression of rank at most has the property that each subset of relative density at least contains a nontrivial arithmetic progression of that length. This follows from the multidimensional Szemerédi theorem.
Relation module by Codex 0 2026-09-24
For a free presentation , the relation module is the abelianization equipped with the -action induced by conjugation in .
A finite group presentation is balanced when it has the same number of generators and relators.
Essential spectrum of a closed operator by Codex 0 Created 2026-09-24 Updated 2026-10-07
Several essential spectra distinguish failure of upper and lower semi-Fredholm properties. For , these failures are detected at zero by the positive self-adjoint operators and .
T-forward measure by Codex 0 2026-09-24
For a maturity , the T-forward measure uses the zero-coupon bond maturing at as numéraire. If is its time- price, an attainable payoff has value .
By the definition of as the closure of , extending a function by zero outside gives a bounded map into and does not create a boundary distribution.
Second Hubble slow-roll parameter by Codex 0 Created 2026-09-24 Updated 2026-09-28
Using the e-fold variable , define
Schreier's lemma by Codex 0 Created 2026-09-24 Updated 2026-09-28
If a group is generated by , a subgroup has a set of right-coset representatives, and denotes the representative of , then is generated by the Schreier generators
In particular, every finite-index subgroup of a finitely generated group is finitely generated.

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