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🔗 Computer science 🔗 Philosophy 🔗 Psychology 🔗 Philosophy/Social and political philosophy 🔗 Philosophy/Philosophy of science 🔗 Philosophy/Contemporary philosophy 🔗 Philosophy/Philosophy of mind 🔗 Sociology 🔗 Cultural Evolution

Memetics is a theory of the evolution of culture based on Darwinian principles with the meme as the unit of culture. The term "meme" was coined by biologist Richard Dawkins in his 1976 book The Selfish Gene, to illustrate the principle that he later called "Universal Darwinism". All evolutionary processes depend on information being copied, varied, and selected, a process also known as variation with selective retention. The information that is copied is called the replicator, and genes are the replicator for biological evolution. Dawkins proposed that the same process drives cultural evolution, and he called this second replicator the "meme". He gave as examples, tunes, catchphrases, fashions, and technologies. Like genes, memes are selfish replicators and have causal efficacy; in other words, their properties influence their chances of being copied and passed on. Some succeed because they are valuable or useful to their human hosts while others are more like viruses.

Just as genes can work together to form co-adapted gene complexes, so groups of memes acting together form co-adapted meme complexes or memeplexes. Memeplexes include (among many other things) languages, traditions, scientific theories, financial institutions, and religions. Dawkins famously referred to religions as "viruses of the mind".

Among proponents of memetics are psychologist Susan Blackmore, author of The Meme Machine, who argues that when our ancestors began imitating behaviours, they let loose a second replicator and co-evolved to become the "meme machines" that copy, vary, and select memes in culture. Philosopher Daniel Dennett develops memetics extensively, notably in his books Darwin's Dangerous Idea, and From Bacteria to Bach and Back. He describes the units of memes as "the smallest elements that replicate themselves with reliability and fecundity." and claims that "Human consciousness is itself a huge complex of memes." In The Beginning of Infinity, physicist David Deutsch contrasts static societies that depend on anti-rational memes suppressing innovation and creativity, with dynamic societies based on rational memes that encourage enlightenment values, scientific curiosity, and progress.

Criticisms of memetics include claims that memes do not exist, that the analogy with genes is false, that the units cannot be specified, that culture does not evolve through imitation, and that the sources of variation are intelligently designed rather than random. Critics of memetics include biologist Stephen Jay Gould who calls memetics a "meaningless metaphor". Philosopher Dan Sperber argues against memetics as a viable approach to cultural evolution because cultural items are not directly copied or imitated but are reproduced. Anthropologist Robert Boyd and biologist Peter Richerson work within the alternative, and more mainstream, field of cultural evolution theory and gene-culture coevolution. Dual inheritance theory has much in common with memetics but rejects the idea that memes are replicators. From this perspective, memetics is seen as just one of several approaches to cultural evolution and one that is generally considered less useful than the alternatives of gene-culture coevolution or dual inheritance theory. The main difference is that dual inheritance theory ultimately depends on biological advantage to genes, whereas memetics treats memes as a second replicator in its own right. Memetics also extends to the analysis of Internet culture and Internet memes.

🔗 Biography 🔗 Internet 🔗 Computing 🔗 Computer science 🔗 Biography/science and academia 🔗 Computing/Computer science 🔗 Computing/Early computers 🔗 Computing/Networking

Jonathan Bruce Postel (; August 6, 1943 – October 16, 1998) was an American computer scientist who made many significant contributions to the development of the Internet, particularly with respect to standards. He is known principally for being the Editor of the Request for Comment (RFC) document series, for Simple Mail Transfer Protocol (SMTP), and for administering the Internet Assigned Numbers Authority (IANA) until his death. In his lifetime he was known as the "god of the Internet" for his comprehensive influence on the medium.

The Internet Society's Postel Award is named in his honor, as is the Postel Center at Information Sciences Institute, University of Southern California. His obituary was written by Vint Cerf and published as RFC 2468 in remembrance of Postel and his work. In 2012, Postel was inducted into the Internet Hall of Fame by the Internet Society. The Channel Islands' Domain Registry building was named after him in early 2016.

🔗 Computer science 🔗 Databases 🔗 Databases/Computer science

R-trees are tree data structures used for spatial access methods, i.e., for indexing multi-dimensional information such as geographical coordinates, rectangles or polygons. The R-tree was proposed by Antonin Guttman in 1984 and has found significant use in both theoretical and applied contexts. A common real-world usage for an R-tree might be to store spatial objects such as restaurant locations or the polygons that typical maps are made of: streets, buildings, outlines of lakes, coastlines, etc. and then find answers quickly to queries such as "Find all museums within 2 km of my current location", "retrieve all road segments within 2 km of my location" (to display them in a navigation system) or "find the nearest gas station" (although not taking roads into account). The R-tree can also accelerate nearest neighbor search for various distance metrics, including great-circle distance.

🔗 Computing 🔗 Computer science 🔗 Computing/Software 🔗 Computing/Computer science

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.

🔗 Computing 🔗 Computer science

In computational complexity and optimization the no free lunch theorem is a result that states that for certain types of mathematical problems, the computational cost of finding a solution, averaged over all problems in the class, is the same for any solution method. The name alludes to the saying "no such thing as a free lunch", that is, no method offers a "short cut". This is under the assumption that the search space is a probability density function. It does not apply to the case where the search space has underlying structure (e.g., is a differentiable function) that can be exploited more efficiently (e.g., Newton's method in optimization) than random search or even has closed-form solutions (e.g., the extrema of a quadratic polynomial) that can be determined without search at all. For such probabilistic assumptions, the outputs of all procedures solving a particular type of problem are statistically identical. A colourful way of describing such a circumstance, introduced by David Wolpert and William G. Macready in connection with the problems of search and optimization, is to say that there is no free lunch. Wolpert had previously derived no free lunch theorems for machine learning (statistical inference). Before Wolpert's article was published, Cullen Schaffer independently proved a restricted version of one of Wolpert's theorems and used it to critique the current state of machine learning research on the problem of induction.

In the "no free lunch" metaphor, each "restaurant" (problem-solving procedure) has a "menu" associating each "lunch plate" (problem) with a "price" (the performance of the procedure in solving the problem). The menus of restaurants are identical except in one regard – the prices are shuffled from one restaurant to the next. For an omnivore who is as likely to order each plate as any other, the average cost of lunch does not depend on the choice of restaurant. But a vegan who goes to lunch regularly with a carnivore who seeks economy might pay a high average cost for lunch. To methodically reduce the average cost, one must use advance knowledge of a) what one will order and b) what the order will cost at various restaurants. That is, improvement of performance in problem-solving hinges on using prior information to match procedures to problems.

In formal terms, there is no free lunch when the probability distribution on problem instances is such that all problem solvers have identically distributed results. In the case of search, a problem instance in this context is a particular objective function, and a result is a sequence of values obtained in evaluation of candidate solutions in the domain of the function. For typical interpretations of results, search is an optimization process. There is no free lunch in search if and only if the distribution on objective functions is invariant under permutation of the space of candidate solutions. This condition does not hold precisely in practice, but an "(almost) no free lunch" theorem suggests that it holds approximately.