"The Hot Troll Deviation" is the title of an episode from the popular TV show *The Big Bang Theory*, specifically season 4, episode 14. In this episode, the characters navigate various personal relationships and social dynamics. The storyline revolves around Raj's interest in a woman he meets online after he gets drunk and posts a risqué photo of himself, which leads to humorous situations. The episode explores themes of attraction and identity through its comedic lens, typical of the show's style.
Input: a sequence of complex numbers .
Output: another sequence of complex numbers such that:
Intuitively, this means that we are braking up the complex signal into sinusoidal frequencies:
  • : is kind of magic and ends up being a constant added to the signal because
  • : sinusoidal that completes one cycle over the signal. The larger the , the larger the resolution of that sinusoidal. But it completes one cycle regardless.
  • : sinusoidal that completes two cycles over the signal
  • ...
  • : sinusoidal that completes cycles over the signal
and is the amplitude of each sine.
We use Zero-based numbering in our definitions because it just makes every formula simpler.
Motivation: similar to the Fourier transform:
In particular, the discrete Fourier transform is used in signal processing after a analog-to-digital converter. Digital signal processing historically likely grew more and more over analog processing as digital processors got faster and faster as it gives more flexibility in algorithm design.
Sample software implementations:
Figure 1.
DFT of with 25 points
. This is a simple example of a discrete Fourier transform for a real input signal. It illustrates how the DFT takes N complex numbers as input, and produces N complex numbers as output. It also illustrates how the discrete Fourier transform of a real signal is symmetric around the center point.
Sponsor updates by Ciro Santilli 40 Updated 2025-07-16
Previously, updates were being done with more focus to sponsors in the format of the child sections to this section. That format is now retired in favor of the more direct Section "Updates" format.
Representation theory by Ciro Santilli 40 Updated 2025-07-16
Basically, a "representation" means associating each group element as an invertible matrices, i.e. a matrix in (possibly some subset of) , that has the same properties as the group.
Or in other words, associating to the more abstract notion of a group more concrete objects with which we are familiar (e.g. a matrix).
Each such matrix then represents one specific element of the group.
This is basically what everyone does (or should do!) when starting to study Lie groups: we start looking at matrix Lie groups, which are very concrete.
Or more precisely, mapping each group element to a linear map over some vector field (which can be represented by a matrix infinite dimension), in a way that respects the group operations:
As shown at Physics from Symmetry by Jakob Schwichtenberg (2015)
Bibliography:
In lattice theory, which is a branch of abstract algebra, a lattice is a partially ordered set (poset) in which any two elements have a unique supremum (least upper bound) and an infimum (greatest lower bound). Theorems in lattice theory often deal with the properties and relationships of these structures.
The AF + BG theorem is a concept in the field of mathematics, specifically in the area of set theory and topology. However, the notation AF + BG does not correspond to a widely recognized theorem or principle within standard mathematical literature or education. It's possible that this notation is specific to a certain context, course, or area of research that is not broadly covered.
Whitehead's Lemma is a result in the field of algebraic topology, particularly in the study of homotopy theory and the properties of topological spaces. It deals with the question of when a certain kind of map induces an isomorphism on homotopy groups.
The Wallace–Bolyai–Gerwien theorem is a result in geometry related to the transformation of polygons. Specifically, it states that any two simple polygons of equal area can be dissected into a finite number of polygonal pieces that can be rearranged to form one another. The theorem has important implications in the study of geometric dissections, a topic that has intrigued mathematicians for centuries.
The Circle Packing Theorem is a result in mathematics that concerns arrangements of circles in a plane. Specifically, the theorem states that given any simple closed curve (a curve that does not intersect itself), it is possible to pack a finite number of circles within that curve such that all the circles are tangent to each other and to the curve.
MacMahon's Master Theorem is a mathematical tool used in the analysis of combinatorial structures, particularly in the enumeration of various combinatorial objects. While it's not as widely known as some other results in combinatorics, it provides a framework for counting partitions, arrangements, and related structures using generating functions. The theorem is named after the British mathematician Percy MacMahon, who made significant contributions to the theory of partitions and generating functions.
Robert May, Baron May of Oxford, is an eminent British scientist known for his significant contributions to the fields of ecology and theoretical biology. Born on April 8, 1936, he is particularly recognized for his work in mathematical ecology, biodiversity, and the dynamics of ecosystems. He served as the Chief Scientific Adviser to the UK government and held the position of President of the Royal Society from 2000 to 2005.
Frank A. Weinhold may refer to a specific individual known for contributions in a certain field, likely in academia or research, given that I don't have specific information on him. As of my last update in October 2021, he was recognized in the domain of chemistry, particularly in the context of chemical education and organometallic chemistry.
Stephen Altschul is a prominent figure in the field of computational biology and bioinformatics. He is known for his work on the development of algorithms and methodologies for analyzing biological data, particularly in the context of sequence alignment and phylogenetic analysis. One of his significant contributions is the development of the BLAST (Basic Local Alignment Search Tool) algorithm, which is widely used for comparing sequences of DNA, RNA, and proteins.
The Journal of Chemical Theory and Computation (JCTC) is a peer-reviewed scientific journal that focuses on the application of computational methods to the field of chemistry.
Gernot Frenking is a prominent chemist known for his work in theoretical and computational chemistry. His research often focuses on the study of electronic structures, reaction mechanisms, and molecular properties using quantum chemical methods. Throughout his career, Frenking has contributed to the understanding of chemical bonding and molecular interactions, and he has published numerous papers in scientific journals. His contributions also extend to the development and application of computational tools in chemistry.

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 2.
    You can publish local OurBigBook lightweight markup files to either https://OurBigBook.com or as a static website
    .
    Figure 3.
    Visual Studio Code extension installation
    .
    Figure 4.
    Visual Studio Code extension tree navigation
    .
    Figure 5.
    Web editor
    . 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.
    Video 4.
    OurBigBook Visual Studio Code extension editing and navigation demo
    . Source.
  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