Unary operation

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In mathematics, a unary operation is an operation with only one operand, i.e. a single input. An example is the function f:\ A\to A, where A is a set. The function f is a unary operation on A.

Common notations are prefix notation (e.g. +, −, not), 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.

Unary negative and positive[edit]

As unary operations have only one operand they are evaluated before other operations containing them[citation needed]. 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)

Examples from Programming Languages[edit]

C family of languages[edit]

In the C family of languages, the following operators are unary:

Unix Shell (Bash)[edit]

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

  • Simple expansion: $x
  • Complex expansion: ${#x}
  • Command substitution: $(cmd)
  • Arithmetic expansion: $((expr))

Other languages[edit]

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

See also[edit]

References[edit]