# Definition:Standard Discrete Metric

## Definition

The standard discrete metric on a set $S$ is the metric satisfying:

$\map d {x, y} = \begin{cases} 0 & : x = y \\ 1 & : x \ne y \end{cases}$

This can be expressed using the Kronecker delta notation as:

$\map d {x, y} = 1 - \delta_{x y}$

The resulting metric space $M = \struct {S, d}$ is the standard discrete metric space on $S$.

## Special Cases

### Real Number Plane

The discrete metric on $\R^2$ is defined as:

$\displaystyle d_0 \left({x, y}\right) := \begin{cases} 0 & : x = y \\ 1 & : \exists i \in \left\{{1, 2}\right\}: x_i \ne y_i \end{cases}$

where $x = \left({x_1, x_2}\right), y = \left({y_1, y_2}\right) \in \R^2$.

## Also known as

This metric is also reported in some texts as the discrete metric.

## Also see

• Results about the standard discrete metric can be found here.

## Linguistic Note

Be careful with the word discrete.

A common homophone horror is to use the word discreet instead.

However, discreet means cautious or tactful, and describes somebody who is able to keep silent for political or delicate social reasons.