local properties of graphs and the hamilton cycle problem
play

Local Properties of Graphs and the Hamilton Cycle Problem Johan de - PowerPoint PPT Presentation

Local Properties of Graphs and the Hamilton Cycle Problem Johan de Wet 1 , 2 and Marietjie Frick 1 1 University of Pretoria 2 DST-NRF Centre of Excellence in Mathematical and Statistical Sciences (CoE-MaSS) Bucharest 2018 Johan de Wet et al. (UP,


  1. The HCP for LT graphs with maximum degree 6 z 1 z 4 z i V(G’) z 2 z 5 Z i is the corresponding Graph G’ z 6 z 3 node in G Z 1 Z 4 Z 2 Graph G Z 5 Z 3 Z 6 Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 11 / 31

  2. The HCP for LT graphs with maximum degree 6 Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 12 / 31

  3. The HCP for LT graphs with maximum degree 6 Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 12 / 31

  4. The HCP for LT graphs with maximum degree 6 Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 12 / 31

  5. The HCP for LT graphs with maximum degree 6 Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 12 / 31

  6. The HCP for LT graphs with maximum degree 6 Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 12 / 31

  7. Locally hamiltonian (LH) graphs Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 13 / 31

  8. Locally hamiltonian (LH) graphs Smallest connected nonhamiltonian LH graph has order 11 and ∆ = 8 (Pareek et al. 1983). Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 13 / 31

  9. Locally hamiltonian (LH) graphs Smallest connected nonhamiltonian LH graph has order 11 and ∆ = 8 (Pareek et al. 1983). Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 13 / 31

  10. Locally hamiltonian (LH) graphs Smallest connected nonhamiltonian LH graph has order 11 and ∆ = 8 (Pareek et al. 1983). HCP NP-complete for ∆ = 9 Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 13 / 31

  11. Hamilton Cycle Problem for LH graphs Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 14 / 31

  12. Hamilton Cycle Problem for LH graphs The HCP for maximally planar graphs is NP-complete (Chv´ atal 1985) Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 14 / 31

  13. Hamilton Cycle Problem for LH graphs The HCP for maximally planar graphs is NP-complete (Chv´ atal 1985) Chv´ atal’s proof is valid for ∆ ≥ 12. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 14 / 31

  14. Hamilton Cycle Problem for LH graphs The HCP for maximally planar graphs is NP-complete (Chv´ atal 1985) Chv´ atal’s proof is valid for ∆ ≥ 12. Theorem (van Aardt et al. 2016) If G is a connected LH graph with ∆( G ) ≤ 6, then G is hamiltonian. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 14 / 31

  15. Hamilton Cycle Problem for LH graphs The HCP for maximally planar graphs is NP-complete (Chv´ atal 1985) Chv´ atal’s proof is valid for ∆ ≥ 12. Theorem (van Aardt et al. 2016) If G is a connected LH graph with ∆( G ) ≤ 6, then G is hamiltonian. There exist connected LH graphs with maximum degree 8 that are nonhamiltonian. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 14 / 31

  16. Locally Hamiltonian Graphs Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 15 / 31

  17. Locally Hamiltonian Graphs Triangle identification G 1 G 2 G v 1 v 2 v u 2 u 1 u w 2 w 1 w Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 15 / 31

  18. Locally Hamiltonian Graphs Triangle identification G 1 G 2 G v 1 v 2 v u 2 u 1 u w 2 w 1 w Theorem Let G 1 and G 2 be two LH graphs, and let G be a graph obtained from G 1 and G 2 by identifying suitable triangles. Then Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 15 / 31

  19. Locally Hamiltonian Graphs Triangle identification G 1 G 2 G v 1 v 2 v u 2 u 1 u w 2 w 1 w Theorem Let G 1 and G 2 be two LH graphs, and let G be a graph obtained from G 1 and G 2 by identifying suitable triangles. Then (a) G is LH . Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 15 / 31

  20. Locally Hamiltonian Graphs Triangle identification G 1 G 2 G v 1 v 2 v u 2 u 1 u w 2 w 1 w Theorem Let G 1 and G 2 be two LH graphs, and let G be a graph obtained from G 1 and G 2 by identifying suitable triangles. Then (a) G is LH . (b) If G 1 and G 2 are planar, then so is G . Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 15 / 31

  21. Locally Hamiltonian Graphs Triangle identification G 1 G 2 G v 1 v 2 v u 2 u 1 u w 2 w 1 w Theorem Let G 1 and G 2 be two LH graphs, and let G be a graph obtained from G 1 and G 2 by identifying suitable triangles. Then (a) G is LH . (b) If G 1 and G 2 are planar, then so is G . (c) If G is hamiltonian, so are both G 1 and G 2 . Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 15 / 31

  22. LH Graphs - the Hamilton Cycle Problem Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 16 / 31

  23. LH Graphs - the Hamilton Cycle Problem Theorem The HCP for LH graphs with ∆ ≥ 9 is NP-complete. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 16 / 31

  24. LH Graphs - the Hamilton Cycle Problem Theorem The HCP for LH graphs with ∆ ≥ 9 is NP-complete. We will use the same approach as for LT graphs. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 16 / 31

  25. LH Graphs - the Hamilton Cycle Problem Theorem The HCP for LH graphs with ∆ ≥ 9 is NP-complete. We will use the same approach as for LT graphs. v 1 H D v 2 x 2 v 3 u 3 x 3 x 1 u 2 u 1 (a) (b) The graph H is locally hamiltonian and nonhamiltonian. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 16 / 31

  26. LH Graphs - the Hamilton Cycle Problem Graph H is combined with two copies of graph D to create the graph F : Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 17 / 31

  27. LH Graphs - the Hamilton Cycle Problem Graph H is combined with two copies of graph D to create the graph F : F i Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 17 / 31

  28. LH Graphs - the Hamilton Cycle Problem Vertices and Nodes and edges in G’ borders in G Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 18 / 31

  29. LH Graphs - the Hamilton Cycle Problem Vertices and Nodes and edges in G’ borders in G Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 18 / 31

  30. LH Graphs - the Hamilton Cycle Problem Vertices and Nodes and edges in G’ borders in G Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 18 / 31

  31. LH Graphs - the Hamilton Cycle Problem z 1 z 4 z i V(G’) z 5 Graph G’ z 2 Z i is the corresponding z 6 z 3 node in G Z 4 Z 1 Graph G Z 2 Z 5 Z 3 Z 6 Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 19 / 31

  32. LH Graphs - the Hamilton Cycle Problem F i Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 20 / 31

  33. LH Graphs - the Hamilton Cycle Problem F i Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 20 / 31

  34. LH Graphs - the Hamilton Cycle Problem F i Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 20 / 31

  35. Locally 2-nested hamiltonian (L2H) graphs Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 21 / 31

  36. Locally 2-nested hamiltonian (L2H) graphs A graph G is L2H if G is LH and � N ( v ) � is LH for any v ∈ V ( G ). Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 21 / 31

  37. Locally 2-nested hamiltonian (L2H) graphs A graph G is L2H if G is LH and � N ( v ) � is LH for any v ∈ V ( G ). Smallest connected nonhamiltonian (L2H) graph has order 13 and ∆ = 10. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 21 / 31

  38. Locally 2-nested hamiltonian (L2H) graphs A graph G is L2H if G is LH and � N ( v ) � is LH for any v ∈ V ( G ). Smallest connected nonhamiltonian (L2H) graph has order 13 and ∆ = 10. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 21 / 31

  39. Locally 2-nested hamiltonian (L2H) graphs A graph G is L2H if G is LH and � N ( v ) � is LH for any v ∈ V ( G ). Smallest connected nonhamiltonian (L2H) graph has order 13 and ∆ = 10. HCP NP-complete for ∆ = 13 Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 21 / 31

  40. L2H Graphs - the Hamilton Cycle Problem z 1 z 4 z i V( G’) Graph G’ z 2 z 5 Z i is the corresponding z 6 z 3 node in G Z 1 Z 4 Graph G Z 5 Z 2 Z 6 Z 3 Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 22 / 31

  41. Locally Hamilton-connected graphs Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 23 / 31

  42. Locally Hamilton-connected graphs A graph G is Hamilton-connected if there is a Hamilton path connecting any two vertices u and v in V ( G ). Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 23 / 31

  43. Locally Hamilton-connected graphs A graph G is Hamilton-connected if there is a Hamilton path connecting any two vertices u and v in V ( G ). Smallest connected nonhamiltonian (LHC) graph has order 15 and ∆ = 11. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 23 / 31

  44. Locally Hamilton-connected graphs A graph G is Hamilton-connected if there is a Hamilton path connecting any two vertices u and v in V ( G ). Smallest connected nonhamiltonian (LHC) graph has order 15 and ∆ = 11. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 23 / 31

  45. Locally Hamilton-connected graphs A graph G is Hamilton-connected if there is a Hamilton path connecting any two vertices u and v in V ( G ). Smallest connected nonhamiltonian (LHC) graph has order 15 and ∆ = 11. HCP NP-complete for ∆ = 15 Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 23 / 31

  46. LHC Graphs - the Hamilton Cycle Problem The graph G ’ The graph G Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 24 / 31

  47. Locally Chv´ atal-Erd¨ os graphs A graph G is Chv´ atal-Erd¨ os if α ( G ) ≤ κ ( G ). Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 25 / 31

  48. Locally Chv´ atal-Erd¨ os graphs A graph G is Chv´ atal-Erd¨ os if α ( G ) ≤ κ ( G ). A graph is locally Chv´ atal-Erd¨ os if α ( � N ( v ) � ) ≤ κ ( � N ( v ) � ) for any v ∈ V ( G ). Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 25 / 31

  49. Locally Chv´ atal-Erd¨ os graphs A graph G is Chv´ atal-Erd¨ os if α ( G ) ≤ κ ( G ). A graph is locally Chv´ atal-Erd¨ os if α ( � N ( v ) � ) ≤ κ ( � N ( v ) � ) for any v ∈ V ( G ). A graph is closed-locally Chv´ atal-Erd¨ os if α ( � N [ v ] � ) ≤ κ ( � N [ v ] � ) for any v ∈ V ( G ). Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 25 / 31

  50. Locally Chv´ atal-Erd¨ os graphs A graph G is Chv´ atal-Erd¨ os if α ( G ) ≤ κ ( G ). A graph is locally Chv´ atal-Erd¨ os if α ( � N ( v ) � ) ≤ κ ( � N ( v ) � ) for any v ∈ V ( G ). A graph is closed-locally Chv´ atal-Erd¨ os if α ( � N [ v ] � ) ≤ κ ( � N [ v ] � ) for any v ∈ V ( G ). A cl-LCE graph is 1-tough (Chen et al. 2013). Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 25 / 31

  51. Locally Chv´ atal-Erd¨ os graphs A graph G is Chv´ atal-Erd¨ os if α ( G ) ≤ κ ( G ). A graph is locally Chv´ atal-Erd¨ os if α ( � N ( v ) � ) ≤ κ ( � N ( v ) � ) for any v ∈ V ( G ). A graph is closed-locally Chv´ atal-Erd¨ os if α ( � N [ v ] � ) ≤ κ ( � N [ v ] � ) for any v ∈ V ( G ). A cl-LCE graph is 1-tough (Chen et al. 2013). It is not known if cl-LCE graphs are hamiltonian. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 25 / 31

  52. Discussion Table: The values of key parameters for various local properties. LC LT LH L2H LHC cl-LCE LCE Minimum n ( G ) if G is not 1-tough 5 7 11 13 15 N/A N/A Minimum ∆( G ) if G is not 1-tough 4 5 8 10 11 N/A N/A HCP is NP-complete for ∆( G ) at least 5 6 9* 13* 15* ? ? Minimum degree of local connectedness 1 1 2 3 3 1 2 *It is not known whether these values are best possible. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 26 / 31

  53. Discussion Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 27 / 31

  54. Discussion We can generalize the concept of L2H graphs to LkH graphs. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 27 / 31

  55. Discussion We can generalize the concept of L2H graphs to LkH graphs. Locally ( k + 1)-connected Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 27 / 31

  56. Discussion We can generalize the concept of L2H graphs to LkH graphs. Locally ( k + 1)-connected The HCP for LkH graphs is NP-complete for any k ≥ 1. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 27 / 31

  57. Discussion We can generalize the concept of L2H graphs to LkH graphs. Locally ( k + 1)-connected The HCP for LkH graphs is NP-complete for any k ≥ 1. The important variable is the relationship between the local connectivity and local independence number. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 27 / 31

  58. Discussion Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 28 / 31

  59. Discussion Oberly-Sumner Conjecture: A connected graph that is locally k -connected and K 1 , k +2 -free is hamiltonian. Johan de Wet et al. (UP, CoE) Local Properties and the HCP Bucharest 2018 28 / 31

Download Presentation
Download Policy: The content available on the website is offered to you 'AS IS' for your personal information and use only. It cannot be commercialized, licensed, or distributed on other websites without prior consent from the author. To download a presentation, simply click this link. If you encounter any difficulties during the download process, it's possible that the publisher has removed the file from their server.

Recommend


More recommend