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euler theorm

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euler theorm

  1. 1. Euler’s theorem and applications Martin B ODIN martin.bodin@ens-lyon.org Euler’s theorem and applications – p. 1
  2. 2. The theorem Euler’s theorem and applications – p. 2
  3. 3. The theoremTheorem. Given a plane graph, if v is the number of vertex,e, the number of edges, and f the number of faces, v−e+f =2 Euler’s theorem and applications – p. 2
  4. 4. The TheoremProof. Consider the plane graph G. Euler’s theorem and applications – p. 3
  5. 5. The TheoremProof. Consider the plane graph G.We consider T , a minimal graph from G, connex. Euler’s theorem and applications – p. 3
  6. 6. The TheoremProof. Consider the plane graph G.We consider T , a minimal graph from G, connex.T is a tree.Thus eT = v − 1, where eT is the number of T ’s edge. Euler’s theorem and applications – p. 3
  7. 7. The TheoremProof. Consider the plane graph G.Then we consider the dual graph. Euler’s theorem and applications – p. 3
  8. 8. The TheoremProof. Consider the plane graph G.Then we consider the dual graph.And the dual D of T . Euler’s theorem and applications – p. 3
  9. 9. The TheoremProof. Consider the plane graph G.Then we consider the dual graph.And the dual D of T .D in a also a tree.Thus eD = f − 1. Euler’s theorem and applications – p. 3
  10. 10. The TheoremProof. Consider the plane graph G.Now, we have eT + eD = e. e = (v − 1) + (f − 1) Euler’s theorem and applications – p. 3
  11. 11. The TheoremProof. Consider the plane graph G.Now, we have eT + eD = e. v−e+f =2 Euler’s theorem and applications – p. 3
  12. 12. Applications Euler’s theorem and applications – p. 4
  13. 13. ApplicationsGiven a plane graph, there exists an edge ofdegree at more 5. Euler’s theorem and applications – p. 4
  14. 14. ApplicationsGiven a plane graph, there exists an edge ofdegree at more 5.Given a finite set of points non all in the sameline, there exists a line that contains only two ofthem. Euler’s theorem and applications – p. 4
  15. 15. Thanks For Your Listenning !Any questions ? Euler’s theorem and applications – p. 5

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