Unary operation

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In mathematics, a unary operation is an operation with only one operand, i.e. a single input. This is in contrast to binary operations, which use two operands. An example is the function f : AA, where A is a set. The function f is a unary operation on A.

Common notations are prefix notation (e.g. +, , ¬), postfix notation (e.g. factorial n!), functional notation (e.g. sin x or sin(x)), and superscripts (e.g. transpose AT). Other notations exist as well. For example, in the case of the square root, a horizontal bar extending the square root sign over the argument can indicate the extent of the argument.

Examples[edit]

Unary negative and positive[edit]

As unary operations have only one operand they are evaluated before other operations containing them. Here is an example using negation:

3 − −2

Here, the first '−' represents the binary subtraction operation, while the second '−' represents the unary negation of the 2 (or '−2' could be taken to mean the integer −2). Therefore, the expression is equal to:

3 − (−2) = 5

Technically there is also a unary positive but it is not needed since we assume a value to be positive:

(+2) = 2

Unary positive does not change the sign of a negative operation:

(+(−2)) = (−2)

In this case a unary negative is needed to change the sign:

(−(−2)) = (+2)

Trigonometry[edit]

In trigonometry the functions , , , and the other trigonometric functions are unary operations. This is because it is possible to input only one term with the operation and retrieve a result, compared with operations, such as addition, where two different terms are needed to compute a result.

Examples from programming languages[edit]

C family of languages[edit]

In the C family of languages, the following operators are unary:[1][2]

Unix Shell (Bash)[edit]

In the Unix/Linux shell (bash/sh), '$' is a unary operator when used for parameter expansion, replacing the name of a variable by its (sometimes modified) value. For example:

  • Simple expansion: $x
  • Complex expansion: ${#x}

Windows PowerShell[edit]

  • Increment: ++$x, $x++
  • Decrement: −−$x, $x−−
  • Positive: +$x
  • Negative: $x
  • Logical negation: -not $x
  • Invoke in current scope: .$x
  • Invoke in new scope: &$x
  • Cast: [type-name] cast-expression
  • Cast: +$x
  • Array: ,$array

See also[edit]

References[edit]

  1. ^ "Chapter 5. Expressions and Operators". C/C++ Language Reference. www-01.ibm.com. Version 6.0. p. 109. Archived from the original on 2012-10-16.
  2. ^ "Unary Operators - C Tutorials - Sanfoundry". www.sanfoundry.com.