Null
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Null is usually that which has no value (nothingness) or no effect. It originates from the Latin word nullus, meaning not any.
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Computer programming
In computer programming, null is a special value for a pointer (or other kind of reference) used to signify that the pointer's target is intentionally not a valid data element. Often, 0 (zero) is used as the null value, as most operating systems consider it an error to try to access such a low memory address. ("Null" also happens to be the German and Norwegian word for zero.)
However, null is used in many other computing disciplines (often interchangeably with nul or nil):
/dev/null, also referred to as the black hole or bit bucket, is a special file on UNIX systems that does nothing with its input and produces no output. The NUL device has similar functionality on DOS and Windows.
In ASCII and Unicode, the code value 0 is the null character.
In some programming languages, such as LISP or Pascal, the designation is called nil.
Programmers using the language C often refer to null values like those listed above. C also supports something called a null pointer.
In many disciplines, the concept of null allows a three-valued logic, with null indicating 'unknown'. For example, this is how NULL is used in the SQL database query language.
Note that this is not the same as the definition of nothing because it is more related to computer science.
See also: Null (SQL), null set, null result, nil
Mathematics
In mathematics, null usually means zero. This is for example used in expressions like null vector.
A mathematical mapping is said to be null potent (or nilpotent) if repeated application can map the whole domain into the null element.
Statistics
In statistics, a null hypothesis is a proposition presumed true unless statistical evidence indicates otherwise. Often it simply asserts the absence of something — for example it may say that a new drug being tested has no effect.
Cryptography
In cryptography, especially classical cryptography, a null is a ciphertext symbol which has no actual meaning, but is intended to confuse the cryptanalyst. Typically, a null will be a character which decrypts to obvious nonsense at the end of an otherwise intelligible phrase. In a null cipher, most of the characters may be nulls.
Electromagnetism
In radio electronics, a null is an area or vector at which the signal from two or more of the antenna elements in an antenna system cancels out almost entirely.
This can be an advantage, as nulls in the horizontal plane can be used to protect other transmitters from interference. If not carefully planned however, nulls can affect the receivability of a signal in any given place. Null fill in the vertical plane is used to prevent this.
Theoretical physics
In the context of special relativity, the adjective null is a synonym of the word light-like.
Scanlation
Null (website (http://www.n-u-l-l.com/)) is a manga scanlation group. They were one of the first groups to continue to translate and release a manga series after it was licensed. One of the manga they translate is the popular One Piece by Eiichiro Oda. The group was founded towards the end of 2002.
See also
External links
- WhatIsNull (http://c2.com/cgi/wiki?WhatIsNull) on the C2 wiki (http://c2.com/cgi/wiki?FrontPage)de:Nullwert