Planar Embeddings of Graphs with Specified Edge Lengths Sergio Cabello GIVE, University Utrecht Erik D. Demaine MIT G¨ unter Rote FU Berlin
Problem and motivation Given a graph G Sergio Cabello, sergio@cs.uu.nl, 2/11
Problem and motivation Given a graph G 3 3 1 2 3 2 1 1 1 1 1 2 2 2 1 1 3 2 and specified edge lengths Question: Can we draw G with these edge lengths? Sergio Cabello, sergio@cs.uu.nl, 2/11
Problem and motivation Applications: • Sensor networks • Structural analysis of molecules • Linear cartograms Sergio Cabello, sergio@cs.uu.nl, 3/11
Our results Restriction to planar embeddings (so planar graphs): • Triangulated graphs ⇒ linear time decision 3-connected ( → fixed topology) unit edge lengths, • ⇒ NP-hard. bounded face degree, and generically rigid 2-connected + unit length, or Improves Eades and Wormald ’90 3-connected also in simplicity Sergio Cabello, sergio@cs.uu.nl, 4/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] ⇒ In R 2 : fixing outer face, the topology is completely fixed. Sergio Cabello, sergio@cs.uu.nl, 5/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] ⇒ In R 2 : fixing outer face, the topology is completely fixed. ⇒ Fixed outer face, incremental treatment of triangles in O ( n ) time. Sergio Cabello, sergio@cs.uu.nl, 5/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] ⇒ In R 2 : fixing outer face, the topology is completely fixed. ⇒ Fixed outer face, incremental treatment of triangles in O ( n ) time. 1 3 2 8 4 5 7 6 Sergio Cabello, sergio@cs.uu.nl, 5/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] ⇒ In R 2 : fixing outer face, the topology is completely fixed. ⇒ Fixed outer face, incremental treatment of triangles in O ( n ) time. 1 3 2 8 4 5 7 6 Sergio Cabello, sergio@cs.uu.nl, 5/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] ⇒ In R 2 : fixing outer face, the topology is completely fixed. ⇒ Fixed outer face, incremental treatment of triangles in O ( n ) time. 1 3 2 8 4 5 7 6 Sergio Cabello, sergio@cs.uu.nl, 5/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] ⇒ In R 2 : fixing outer face, the topology is completely fixed. ⇒ Fixed outer face, incremental treatment of triangles in O ( n ) time. 1 3 2 8 4 5 7 6 Sergio Cabello, sergio@cs.uu.nl, 5/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] ⇒ In R 2 : fixing outer face, the topology is completely fixed. ⇒ Fixed outer face, incremental treatment of triangles in O ( n ) time. 1 3 2 8 4 5 7 6 Sergio Cabello, sergio@cs.uu.nl, 5/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] ⇒ In R 2 : fixing outer face, the topology is completely fixed. ⇒ Fixed outer face, incremental treatment of triangles in O ( n ) time. 1 3 2 8 4 5 7 6 Sergio Cabello, sergio@cs.uu.nl, 5/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] ⇒ In R 2 : fixing outer face, the topology is completely fixed. ⇒ Fixed outer face, incremental treatment of triangles in O ( n ) time. 1 3 2 8 4 5 7 6 Sergio Cabello, sergio@cs.uu.nl, 5/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] ⇒ In R 2 : fixing outer face, the topology is completely fixed. ⇒ Fixed outer face, incremental treatment of triangles in O ( n ) time. 1 3 2 8 4 5 7 6 Sergio Cabello, sergio@cs.uu.nl, 5/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] ⇒ In R 2 : fixing outer face, the topology is completely fixed. ⇒ Fixed outer face, incremental treatment of triangles in O ( n ) time. 1 3 2 8 4 5 7 6 Longest edge in the outermost face ⇒ Two outer face candidates. Sergio Cabello, sergio@cs.uu.nl, 5/11
Triangulated graphs Planar triangulation ⇒ Planar 3-connected Planar 3-connected ⇒ One topological embedding in S 2 [Whitney] . e ⇒ In R 2 : fixing outer face, m the topology is completely fixed. i t r ⇒ Fixed outer face, incremental treatment of triangles in O ( n ) time. a e n 1 3 2 8 i 4 L 5 7 6 Longest edge in the outermost face ⇒ Two outer face candidates. Sergio Cabello, sergio@cs.uu.nl, 5/11
NP-hardness Th: It is NP-hard for planar 3-connected graphs. Reduction from planar 3-SAT v 1 v 2 v 3 v 4 v 5 v n . . . Sergio Cabello, sergio@cs.uu.nl, 6/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness v 3 v 4 v 5 The holder gadget. Sergio Cabello, sergio@cs.uu.nl, 7/11
NP-hardness The variable gadget. v 3 v 4 v 5 (true literal ≡ pushing towards variable) ¬ v i v i v i v i ≡ true ¬ v i v i v i Sergio Cabello, sergio@cs.uu.nl, 8/11
NP-hardness The variable gadget. v 3 v 4 v 5 (true literal ≡ pushing towards variable) ¬ v i v i v i v i ≡ false ¬ v i v i v i Sergio Cabello, sergio@cs.uu.nl, 8/11
NP-hardness The inverter gadget. pushing towards variable v 3 v 4 v 5 � pushing towards clause Sergio Cabello, sergio@cs.uu.nl, 9/11
NP-hardness The inverter gadget. pushing towards variable v 3 v 4 v 5 � pushing towards clause Sergio Cabello, sergio@cs.uu.nl, 9/11
NP-hardness The inverter gadget. pushing towards variable v 3 v 4 v 5 � pushing towards clause Sergio Cabello, sergio@cs.uu.nl, 9/11
NP-hardness The clause gadget. v 3 v 4 v 5 (realizable ⇔ ∃ literal pushing towards clause) l i ≡ false l j ≡ false the same l k ≡ false Sergio Cabello, sergio@cs.uu.nl, 10/11
NP-hardness The clause gadget. v 3 v 4 v 5 (realizable ⇔ ∃ literal pushing towards clause) l i ≡ true l j ≡ false l k ≡ false Sergio Cabello, sergio@cs.uu.nl, 10/11
NP-hardness The clause gadget. v 3 v 4 v 5 (realizable ⇔ ∃ literal pushing towards clause) l i ≡ true l j ≡ true l k ≡ true Sergio Cabello, sergio@cs.uu.nl, 10/11
NP-hardness The clause gadget. v 3 v 4 v 5 (realizable ⇔ ∃ literal pushing towards clause) l i ≡ false l j ≡ false l k ≡ true Sergio Cabello, sergio@cs.uu.nl, 10/11
What did I explain? Planar drawing of graphs with specified edge lengths. • ⇒ linear time decision Triangulated graphs 3-connected ( → fixed topology) unit edge lengths, • ⇒ NP-hard. bounded face degree, and generically rigid Sergio Cabello, sergio@cs.uu.nl, 11/11
Contents • Problem and motivation • Our results • Triangulated graphs • NP-hardness • What did I explain? Sergio Cabello, sergio@cs.uu.nl, 12/11
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