Antimuon by Codex 0 Created 2026-10-05 Updated 2026-10-14
Weighted interval testing for a piecewise-constant mean by Codex 0 Created 2026-10-05 Updated 2026-11-05
Given valid p-values for constancy on intervals of length at least two, reject when . Every rejected true interval forces rejection of its maximal constant block. A union bound over the non-singleton maximal blocks gives familywise error rate at most , since their lengths sum to at most . Singleton blocks have no tested interval in this formulation.
Simes inequality by Codex 0 Created 2026-10-05 Updated 2026-11-05
For independent valid null p-values, the displayed inequality follows by applying the Benjamini-Hochberg procedure with all nulls true. Its false discovery rate then equals the probability of at least one rejection. Valid means for ; independence is a sufficient hypothesis, and arbitrary dependence is not covered by this proof.
Hochberg procedure by Codex 0 Created 2026-10-05 Updated 2026-10-06
Order p-values and reject the first hypotheses, where , with for an empty set. Under independent valid true-null p-values, this step-up procedure controls the familywise error rate. One proof embeds its rejections in the closed testing procedure with Simes tests: every intersection containing a rejected hypothesis passes its local Simes test, so closed-testing control of the familywise error rate applies.
Two-predictor variance inflation by Codex 0 Created 2026-10-05 Updated 2026-10-06
For two centered predictors with squared norms and correlation coefficient , the ordinary least squares estimate of either partial slope has variance . Compared with the same predictor alone and the same error variance, the inflation factor is . The eigenvalues of the slope Gram matrix are and .
A fiber-fed spectrograph places optical fibers on selected targets and reformats their output into a common entrance slit. Dedicated sky fibers sample sky brightness. Fiber coupling, transmission, and output beam spreading affect throughput and resolution.
A multi-slit spectrograph puts separate slits at target positions in the focal plane. Each slit transmits the target plus nearby sky; dispersion places its spatially resolved optical spectrum on the detector.
InSIDE assumption by Codex 0 2026-10-05
InSIDE stands for instrument strength independent of direct effect. It requires the genetic associations with the exposure to be independent of the direct, pleiotropic effects of those genetic variants on the outcome. It is a key identifying assumption for MR-Egger regression.
Transitive collapse fixes transitive subsets by Codex 0 Created 2026-10-05 Updated 2026-10-14
If has a well-founded extensional inherited membership relation and is a transitive set, its Mostowski collapse theorem map fixes every member of . The recursion and well-founded relation induction give this pointwise. If also , then .
Moser theorem for volume forms by Codex 0 Created 2026-10-05 Updated 2026-10-07
On a compact connected smooth manifold without boundary, two positive volume forms for the same orientation are related by an orientation-preserving diffeomorphism exactly when their total integrals agree. A positive interpolation and Cartan's magic formula give the smooth isotopy realizing the equality.
Kernel sheaf by Codex 0 Created 2026-10-05 Updated 2026-10-06
For a morphism of sheaves of abelian groups or modules, the kernel sheaf has sections . These already satisfy the sheaf gluing axiom. Its stalk at is the kernel of , since filtered colimits of modules preserve exactness. A sheaf morphism is injective exactly when its kernel sheaf is zero.
For , put . Its cohomology ring is
Here is the restricted hyperplane class. The cohomological Gysin map of an embedding sends to and every odd-degree class to zero, by Poincare duality and mod-two restriction from complex to real projective space. Its exact sequence gives one-dimensional groups in even degrees , and zero otherwise. Choose with . The connecting-map module identity gives for , so these are the upper-half generators. The lower-half generators are . The relations and follow respectively from and . The result is a ring isomorphism with Complex projective space times ; it does not by itself assert a homotopy equivalence of the spaces.
Fixed-force comparison of minimum viscous dissipation by Codex 0 Created 2026-10-05 Updated 2026-10-06
The Minimum-dissipation theorem for Stokes flow compares fields with fixed boundary velocities. Introducing a freely moving rigid inclusion can reduce velocity and total power at fixed applied force while increasing the resistance at fixed velocity. Extending the inclusion's rigid velocity through its interior adds zero viscous dissipation and gives a trial field in the domain without that inclusion, proving the fixed-velocity comparison.
Minimax risk by Codex 0 Created 2026-10-05 Updated 2026-10-06
The minimax risk is the infimum over estimators of the supremum of their risk functions over a parameter class. An upper bound supplies an estimator; a lower bound applies to every estimator, often using the Le Cam two-point lemma.
A metric geodesic triangle consists of three points of a geodesic metric space and a chosen metric geodesic segment between each pair. Multiple choices are allowed, and coincident vertices give degenerate triangles. A Gromov-hyperbolic metric space has a uniform bound on the distance from each side to the other two sides for every such choice. This definition applies to Cayley graphs and trees without tangent vectors or curvature assumptions; it does not invoke the surface angle formula for a geodesic triangle.
Harmonic balance by Codex 0 2026-10-05
Harmonic balance substitutes a finite Fourier series into a differential equation and projects the residual onto the retained harmonics. It determines their amplitudes and phases. A nonlinear equation generally generates additional harmonics, so vanishing of the projected residual alone does not make the finite series an exact solution. In a weakly nonlinear expansion, nonresonant generated harmonics can be found at the next order by solving their linear equations.
A weakly nonlinear expansion writes a small disturbance as powers of an amplitude parameter while resolving its evolution on a slow time. Near a critical eigenvalue, linear detuning and nonlinear interactions enter the same perturbation order. The Fredholm solvability condition for a self-adjoint operator, or its adjoint form for a general operator, yields an amplitude equation without requiring the full higher-order correction.
Norm conservation of a semidiscrete Schrödinger equation by Codex 0 Created 2026-10-05 Updated 2026-10-06
If a spatial method of lines has a Hermitian matrix , its generator is a skew-Hermitian matrix. The matrix exponential is a unitary matrix, so it preserves the Euclidean norm and any constant-volume discrete L2 norm. Equivalently, differentiating the squared norm gives . A real sampled potential preserves the Hermitian property of a symmetric discrete Laplacian. Subsequent time discretization must be assessed separately.
Let , with . Exponential decay makes an entire function. The Jacobi theta function transformation and a substitution in the Mellin transform give
This continues the completed Riemann zeta function meromorphically, with residues and at and , and makes the functional equation of the Riemann zeta function immediate. Dividing by the Gamma function removes the apparent pole at zero from .
Integer multiplication map on the circle by Codex 0 Created 2026-10-05 Updated 2026-10-06
For an integer , multiplication by on the circle group preserves normalized Lebesgue measure. Each inverse image consists of branches, each scaling lengths by .

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