# Dilation (metric space)

In mathematics, a dilation is a function $f$ from a metric space into itself that satisfies the identity

$d(f(x),f(y))=rd(x,y)$

for all points $(x, y)$, where $d(x, y)$ is the distance from $x$ to $y$ and $r$ is some positive real number.

In Euclidean space, such a dilation is a similarity of the space. Dilations change the size but not the shape of an object or figure.

Every dilation of a Euclidean space that is not a congruence has a unique fixed point that is called the center of dilation. Some congruences have fixed points and others do not.
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