Properties of Floor Function

Theorem

This page gathers together some basic propeties of the floor function.

Floor is between Number and One Less

$x - 1 < \floor x \le x$

where $\floor x$ denotes the floor of $x$.

Floor of Number plus Integer

$\forall n \in \Z: \floor x + n = \floor {x + n}$

Real Number minus Floor

$x - \floor x \in \hointr 0 1$

Real Number is between Floor Functions

$\forall x \in \R: \floor x \le x < \floor {x + 1}$

Real Number is Floor plus Difference

There exists an integer $n \in \Z$ such that for some $t \in \hointr 0 1$:

$x = n + t$

if and only if:

$n = \floor x$

Floor Function is Idempotent

$\floor {\floor x} = \floor x$

Range of Values of Floor Function

Number less than Integer iff Floor less than Integer

$\floor x < n \iff x < n$

Number not less than Integer iff Floor not less than Integer

$x \ge n \iff \floor x \ge n$

Integer equals Floor iff between Number and One Less

$\floor x = n \iff x - 1 < n \le x$

Integer equals Floor iff Number between Integer and One More

$\floor x = n \iff n \le x < n + 1$

Also see

• Properties of Ceiling Function