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Allen's interval algebra is a calculus for temporal reasoning that was introduced by James F. Allen in 1983. The calculus defines possible relations between time intervals and provides a composition table that can be used as a basis for reasoning about temporal descriptions of events.
In summary, a set of the real numbers is an interval, if and only if it is an open interval, a closed interval, or a half-open interval. [4] [5] A degenerate interval is any set consisting of a single real number (i.e., an interval of the form [a, a]). [6] Some authors include the empty set in this definition.
The main objective of interval arithmetic is to provide a simple way of calculating upper and lower bounds of a function's range in one or more variables. These endpoints are not necessarily the true supremum or infimum of a range since the precise calculation of those values can be difficult or impossible; the bounds only need to contain the function's range as a subset.
Interval class Play ⓘ.. In musical set theory, an interval class (often abbreviated: ic), also known as unordered pitch-class interval, interval distance, undirected interval, or "(even completely incorrectly) as 'interval mod 6'" (Rahn 1980, 29; Whittall 2008, 273–74), is the shortest distance in pitch class space between two unordered pitch classes.
Since () is a sequence of nested intervals, the interval lengths get arbitrarily small; in particular, there exists an interval with a length smaller than . But from s ∈ I n {\displaystyle s\in I_{n}} one gets s − a n < s − σ {\displaystyle s-a_{n}<s-\sigma } and therefore a n > σ {\displaystyle a_{n}>\sigma } .
All-interval tetrachords (Play ⓘ). An all-interval tetrachord is a tetrachord, a collection of four pitch classes, containing all six interval classes. [1] There are only two possible all-interval tetrachords (to within inversion), when expressed in prime form. In set theory notation, these are [0,1,4,6] (4-Z15) [2] and [0,1,3,7] (4-Z29). [3]
The notation is also used to denote the characteristic function in convex analysis, which is defined as if using the reciprocal of the standard definition of the indicator function. A related concept in statistics is that of a dummy variable .
The dramatic clout of the interval was further exploited by operatic composers during the nineteenth century. Robert Donington (1963, p. 175) heard the dark, atmospheric Prelude to Wagner ’s opera Siegfried as "a kind of elemental brooding…Its material is an uneasy sequence of thirds low in the bass, and separated by a diminished seventh ...