A* search algorithm

In computer science, A* (pronounced as "A star" ( listen)) is a computer algorithm that is widely used in pathfinding and graph traversal, the process of plotting an efficiently traversable path between multiple points, called nodes. Noted for its performance and accuracy, it enjoys widespread use. However, in practical travel-routing systems, it is generally outperformed by algorithms which can pre-process the graph to attain better performance, although other work has found A* to be superior to other approaches.

Peter Hart, Nils Nilsson and Bertram Raphael of Stanford Research Institute (now SRI International) first described the algorithm in 1968. It is an extension of Edsger Dijkstra's 1959 algorithm. A* achieves better performance by using heuristics to guide its search.

History

In 1968, AI researcher Nils Nilsson was trying to improve the path planning done by Shakey the Robot, a prototype robot that could navigate through a room containing obstacles. This path-finding algorithm, that Nilsson called A1, was a faster version of the then best known method, Dijkstra's algorithm, for finding shortest paths in graphs. Bertram Raphael suggested some significant improvements upon this algorithm, calling the revised version A2. Then Peter E. Hart introduced an argument that established A2, with only minor changes, to be the best possible algorithm for finding shortest paths. Hart, Nilsson and Raphael then jointly developed a proof that the revised A2 algorithm was optimal for finding shortest paths under certain well-defined conditions.

180

Year 180 (CLXXX) was a leap year starting on Friday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Rusticus and Condianus (or, less frequently, year 933 Ab urbe condita). The denomination 180 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

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Roman Empire

Prince

A prince is a male ruler, monarch, or member of a monarch's or former monarch's family. Prince is also a hereditary title in the nobility of some European states. The feminine equivalent is a princess. The English word derives, via the French word prince, from the Latin noun princeps, from primus (first) + capio (to seize), meaning "the chief, most distinguished, ruler, prince".

Historical background

The Latin word prīnceps (older Latin *prīsmo-kaps, literally "the one who takes the first [place/position]"), became the usual title of the informal leader of the Roman senate some centuries before the transition to empire, the princeps senatus.

Emperor Augustus established the formal position of monarch on the basis of principate, not dominion. He also tasked his grandsons as summer rulers of the city when most of the government were on holiday in the country or attending religious rituals, and, for that task, granted them the title of princeps.

The title has generic and substantive meanings:

Star

A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun. Other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, and the brightest stars gained proper names. Extensive catalogues of stars have been assembled by astronomers, which provide standardized star designations.

For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and then radiates into outer space. Once the hydrogen in the core of a star is nearly exhausted, almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the star's lifetime and, for some stars, by supernova nucleosynthesis when it explodes. Near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity (chemical composition), and many other properties of a star by observing its motion through space, luminosity, and spectrum respectively. The total mass of a star is the principal determinant of its evolution and eventual fate. Other characteristics of a star, including diameter and temperature, change over its life, while the star's environment affects its rotation and movement. A plot of the temperature of many stars against their luminosities, known as a Hertzsprung–Russell diagram (H–R diagram), allows the age and evolutionary state of a star to be determined.

Michael Jackson

Michael Joseph Jackson (August 29, 1958 – June 25, 2009) was an American singer, songwriter, record producer, dancer, and actor. Called the King of Pop, his contributions to music and dance, along with his publicized personal life, made him a global figure in popular culture for over four decades.

The eighth child of the Jackson family, he debuted on the professional music scene along with his elder brothers Jackie, Tito, Jermaine, and Marlon as a member of the Jackson 5 in 1964, and began his solo career in 1971. In the early 1980s, Jackson became a dominant figure in popular music. The music videos for his songs, including those of "Beat It", "Billie Jean", and "Thriller" from his 1982 album Thriller, were credited with breaking down racial barriers and with transforming the medium into an art form and promotional tool. The popularity of these videos helped to bring the then-relatively-new television channel MTV to fame. His 1987 album Bad spawned the U.S. Billboard Hot 100 number-one singles "I Just Can't Stop Loving You", "Bad", "The Way You Make Me Feel", "Man in the Mirror", and "Dirty Diana", becoming the first album to have five number-one singles on the Billboard Hot 100. With videos such as "Black or White" and "Scream", he continued to innovate the medium throughout the 1990s, as well as forging a reputation as a touring solo artist. Through stage and video performances, Jackson popularized a number of complicated dance techniques, such as the robot and the moonwalk, to which he gave the name. His distinctive sound and style has influenced numerous artists of various music genres.