what does [[x]] mean

Question

anonymous · Answer

I believe it means the greatest integer function or nearest integer function.

asnaseer · Answer

(1) $\lfloor x\rfloor$ is the floor function - i.e. largest integer $\le x$
(2) $\lceil x\rceil$ is the ceiling function - i.e. smallest integer $\ge x$
(3) $\lfloor x\rceil$ is the nearest integer function

Examples of (1)
$\lfloor 2.9\rfloor=2$, $\lfloor 2\rfloor=2$, $\lfloor 2.1\rfloor=2$, $\lfloor -2.1\rfloor=-3$

Examples of (2)
$\lceil 2.9\rceil=3$, $\lceil 2\rceil=2$, $\lceil 2.1\rceil=3$, $\lceil -2.1\rceil=-2$

Examples of (3)
$\lfloor 2.9\rceil=3$, $\lfloor 2\rceil=2$, $\lfloor 2.1\rceil=2$, $\lfloor -2.1\rceil=-2$

(1) is also sometimes written as: $[x]$, floor$x$) or int($x$)
(3) is also sometimes written as: $[x]$, Round($x$), nint($x$) or $||x||$

So you can see that $[x]$ can be ambiguous as it can mean (1) or (3).