In mathematics, a unary operation is an operation with only one operand, i.e. a single input.[1] This is in contrast to binary operations, which use two operands.[2] An example is any function f : A → A, 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.
Obtaining the absolute value of a number is a unary operation. This function is defined as [math]\displaystyle{ |n| = \begin{cases} n, & \mbox{if } n\geq0 \\ -n, & \mbox{if } n\lt 0 \end{cases} }[/math][3] where [math]\displaystyle{ |n| }[/math] is the absolute value of [math]\displaystyle{ n }[/math].
This is used to find the negative value of a single number. Here are some examples:
As unary operations have only one operand they are evaluated before other operations containing them. Here is an example using negation:
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:
Technically, there is also a unary + operation but it is not needed since we assume an unsigned value to be positive:
The unary + operation does not change the sign of a negative operation:
In this case, a unary negation is needed to change the sign:
In trigonometry, the trigonometric functions, such as [math]\displaystyle{ \sin }[/math], [math]\displaystyle{ \cos }[/math], and [math]\displaystyle{ \tan }[/math], can be seen as unary operations. This is because it is possible to provide only one term as input for these functions and retrieve a result. By contrast, binary operations, such as addition, require two different terms to compute a result.
In JavaScript, these operators are unary:[4]
++x
, x++
--x
, x--
+x
-x
~x
!x
In the C family of languages, the following operators are unary:[5][6]
++x
, x++
--x
, x--
&x
*x
+x
-x
~x
!x
sizeof x, sizeof(type-name)
(type-name) cast-expression
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:
$x
${#x}
++$x
, $x++
--$x
, $x--
+$x
-$x
!$x
.$x
&$x
[type-name] cast-expression
+$x
,$array
Original source: https://en.wikipedia.org/wiki/Unary operation.
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