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🔗 MU puzzle
The MU puzzle is a puzzle stated by Douglas Hofstadter and found in Gödel, Escher, Bach involving a simple formal system called "MIU". Hofstadter's motivation is to contrast reasoning within a formal system (ie., deriving theorems) against reasoning about the formal system itself. MIU is an example of a Post canonical system and can be reformulated as a string rewriting system.
Discussed on
- "MU puzzle" | 2018-12-15 | 83 Upvotes 45 Comments
🔗 $100 Billion USD oops
The 2018 Samsung fat-finger error was a fat-finger error on April 8th 2018 in which an employee of Samsung Securities mistakenly distributed shares worth US$100,000,000,000 to employees. The company is the stock trading arm of the Samsung conglomerate and is engaged in financial services including securities and investment banking sectors primarily in Korea, China, the United States, the United Kingdom, Japan, and Hong Kong.
Discussed on
- "$100 Billion USD oops" | 2018-12-14 | 18 Upvotes 18 Comments
🔗 Slow television
Slow television, or slow TV (Norwegian: Sakte-TV), is a term used for a genre of "marathon" television coverage of an ordinary event in its complete length. Its name is derived both from the long endurance of the broadcast as well as from the natural slow pace of the television program's progress. It was popularised in the 2000s by the Norwegian Broadcasting Corporation (NRK), beginning with the broadcast of a 7-hour train journey in 2009.
Discussed on
- "Slow television" | 2018-12-02 | 36 Upvotes 10 Comments
🔗 Shoelace formula
The shoelace formula or shoelace algorithm (also known as Gauss's area formula and the surveyor's formula) is a mathematical algorithm to determine the area of a simple polygon whose vertices are described by their Cartesian coordinates in the plane. The user cross-multiplies corresponding coordinates to find the area encompassing the polygon, and subtracts it from the surrounding polygon to find the area of the polygon within. It is called the shoelace formula because of the constant cross-multiplying for the coordinates making up the polygon, like tying shoelaces. It is also sometimes called the shoelace method. It has applications in surveying and forestry, among other areas.
The formula was described by Meister (1724–1788) in 1769 and by Gauss in 1795. It can be verified by dividing the polygon into triangles, and can be considered to be a special case of Green's theorem.
The area formula is derived by taking each edge AB, and calculating the area of triangle ABO with a vertex at the origin O, by taking the cross-product (which gives the area of a parallelogram) and dividing by 2. As one wraps around the polygon, these triangles with positive and negative area will overlap, and the areas between the origin and the polygon will be cancelled out and sum to 0, while only the area inside the reference triangle remains. This is why the formula is called the surveyor's formula, since the "surveyor" is at the origin; if going counterclockwise, positive area is added when going from left to right and negative area is added when going from right to left, from the perspective of the origin.
The area formula can also be applied to self-overlapping polygons since the meaning of area is still clear even though self-overlapping polygons are not generally simple. Furthermore, a self-overlapping polygon can have multiple "interpretations" but the Shoelace formula can be used to show that the polygon's area is the same regardless of the interpretation.
Discussed on
- "Shoelace formula" | 2018-12-02 | 73 Upvotes 12 Comments
- "Shoelace Formula" | 2014-12-26 | 27 Upvotes 3 Comments
🔗 Direct Democracy in Switzerland
Switzerland, officially the Swiss Confederation, is a country situated in the confluence of Western, Central, and Southern Europe. It is a federal republic composed of 26 cantons, with federal authorities seated in Bern. Switzerland is a landlocked country bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. It is geographically divided among the Swiss Plateau, the Alps, and the Jura, spanning a total area of 41,285 km2 (15,940 sq mi), and land area of 39,997 km2 (15,443 sq mi). While the Alps occupy the greater part of the territory, the Swiss population of approximately 8.5 million is concentrated mostly on the plateau, where the largest cities are located, among them the two global cities and economic centres of Zürich and Geneva.
The establishment of the Old Swiss Confederacy dates to the late medieval period, resulting from a series of military successes against Austria and Burgundy. Swiss independence from the Holy Roman Empire was formally recognized in the Peace of Westphalia in 1648. The Federal Charter of 1291 is considered the founding document of Switzerland which is celebrated on Swiss National Day. Since the Reformation of the 16th century, Switzerland has maintained a strong policy of armed neutrality; it has not fought an international war since 1815 and did not join the United Nations until 2002. Nevertheless, it pursues an active foreign policy and is frequently involved in peace-building processes around the world. Switzerland is the birthplace of the Red Cross, one of the world's oldest and best known humanitarian organisations, and is home to numerous international organisations, including the second largest UN office. It is a founding member of the European Free Trade Association, but notably not part of the European Union, the European Economic Area or the Eurozone. However, it participates in the Schengen Area and the European Single Market through bilateral treaties.
Switzerland occupies the crossroads of Germanic and Romance Europe, as reflected in its four main linguistic and cultural regions: German, French, Italian and Romansh. Although the majority of the population are German-speaking, Swiss national identity is rooted in a common historical background, shared values such as federalism and direct democracy, and Alpine symbolism. Due to its linguistic diversity, Switzerland is known by a variety of native names: Schweiz [ˈʃvaɪts] (German); Suisse [sɥis(ə)] (French); Svizzera [ˈzvittsera] (Italian); and Svizra [ˈʒviːtsrɐ, ˈʒviːtsʁɐ] (Romansh). On coins and stamps, the Latin name, Confoederatio Helvetica – frequently shortened to "Helvetia" – is used instead of the four national languages.
The sovereign state is one of the most developed countries in the world, with the highest nominal wealth per adult and the eighth-highest per capita gross domestic product. It ranks at or near the top in several international metrics, including economic competitiveness and human development. Zürich, Geneva and Basel have been ranked among the top ten cities in the world in terms of quality of life, with Zürich ranked second globally. In 2019, IMD placed Switzerland first in the world in attracting skilled workers. World Economic Forum ranks it the 5th most competitive country globally.
Discussed on
- "Direct Democracy in Switzerland" | 2018-12-01 | 84 Upvotes 104 Comments
🔗 Space Infrastructure Servicing
Space Infrastructure Servicing (SIS) is a spacecraft being developed by Canadian aerospace firm MacDonald, Dettwiler and Associates to operate as a small-scale in-space refueling depot for communication satellites in geosynchronous orbit.
In June 2017, SSL announced its first commercial customer, Luxembourg-based satellite owner/operator SES S.A.
Discussed on
- "Space Infrastructure Servicing" | 2018-11-25 | 24 Upvotes 4 Comments
🔗 Airglow
Airglow (also called nightglow) is a faint emission of light by a planetary atmosphere. In the case of Earth's atmosphere, this optical phenomenon causes the night sky never to be completely dark, even after the effects of starlight and diffused sunlight from the far side are removed.
Discussed on
- "Airglow" | 2018-11-24 | 79 Upvotes 8 Comments
🔗 Induction of regular languages
In computational learning theory, induction of regular languages refers to the task of learning a formal description (e.g. grammar) of a regular language from a given set of example strings. Although Mark E. Gold has shown that not every regular language can be learned this way (see language identification in the limit), approaches have been investigated for a variety of subclasses. They are sketched in this article. For learning of more general grammars, see Grammar induction.
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- "Induction of regular languages" | 2018-11-24 | 44 Upvotes 3 Comments
🔗 THX 1138
THX 1138 is a 1971 American social science fiction film directed by George Lucas in his feature film directorial debut. It is set in a dystopian future in which the populace is controlled through android police and mandatory use of drugs that suppress emotions. Produced by Francis Ford Coppola and written by Lucas and Walter Murch, it stars Robert Duvall and Donald Pleasence.
THX 1138 was developed from Lucas's student film Electronic Labyrinth: THX 1138 4EB, which he made in 1967 while attending the USC School of Cinematic Arts. The feature film was produced in a joint venture between Warner Bros. and American Zoetrope. A novelization by Ben Bova was published in 1971. The film received mixed reviews from critics and failed to find box-office success on initial release; however, the film has subsequently received critical acclaim and gained a cult following, particularly in the aftermath of Lucas' success with Star Wars in 1977.
🔗 Rabin-Karp Algorithm for finding matching substrings in text
In computer science, the Rabin–Karp algorithm or Karp–Rabin algorithm is a string-searching algorithm created by Richard M. Karp and Michael O. Rabin (1987) that uses hashing to find an exact match of a pattern string in a text. It uses a rolling hash to quickly filter out positions of the text that cannot match the pattern, and then checks for a match at the remaining positions. Generalizations of the same idea can be used to find more than one match of a single pattern, or to find matches for more than one pattern.
To find a single match of a single pattern, the expected time of the algorithm is linear in the combined length of the pattern and text, although its worst-case time complexity is the product of the two lengths. To find multiple matches, the expected time is linear in the input lengths, plus the combined length of all the matches, which could be greater than linear. In contrast, the Aho–Corasick algorithm can find all matches of multiple patterns in worst-case time and space linear in the input length and the number of matches (instead of the total length of the matches).
A practical application of the algorithm is detecting plagiarism. Given source material, the algorithm can rapidly search through a paper for instances of sentences from the source material, ignoring details such as case and punctuation. Because of the abundance of the sought strings, single-string searching algorithms are impractical.
Discussed on
- "Rabin-Karp Algorithm for finding matching substrings in text" | 2018-11-20 | 10 Upvotes 1 Comments