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Hausdorff dimension

Hausdorff dimension is a method of measuring the dimension of a metric space. It is always a non-negative real number, but it need not be an integer; one way to define a fractal? is a metric space with a fractional (non-integral) Hausdorff dimension.

The Hausdorff dimension of the cartesian space ${ℝ}^n$ (or any inhabited open subset thereof) is $n$. The Hausdorff dimension of a self-similar fractal which consists of $n$ copies of itself reduced in size by a factor of $m$ is ${\log }_{m}n$.

In general, Hausdorff dimension may be defined using Hausdorff measure?. See Wikipedia.