Definition:Euler Characteristic

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Graphs

Let $X = \left({V, E}\right)$ be a graph.

Let $X$ be embedded in a surface.


The Euler Characteristic of a $X$ is written $\chi \left({X}\right)$ and is defined as:

$\chi \left({X}\right) = v - e + f$

where:

  • $v = \left|{V}\right|$ is the number of vertices;
  • $e = \left|{E}\right|$ is the number of edges;
  • $f$ is the number of faces.


Euler Polyhedron Formula

The Euler Polyhedron Formula states that for any planar graph (i.e. which can be drawn on a sphere or plane without any two of its edges meeting except at vertices), $\chi = 2$.


Generalized Formula




Source of Name

This entry was named for Leonhard Paul Euler.

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