Search for tag: "cs598jge"

∞. Chasing puppies

a. The puppy problem b. Special cases: blind vs. stubborn, puppies vs. guppies c. Configurations and the puppy diagram (Look, actual code!) d. Counting essential critical cycles e. Rubber bands on a…

From  Jeff Erickson 24 plays 0  

26. Planarizing and separating surface maps

a. Shortest non-separating cycles b. Menger's theorem c. Planarizing with at most g cycles via cycles: O(sqrt{gn} log g) d. Greedy tree-cotree again again e. Planarixing via level slicing and…

From  Jeff Erickson 10 plays 0  

25. Approximation schemes via slicing

a. Carvings b. Branch decompositions c. Dynamic programming c. Radial and medial maps d. Radial greedy tree-cotree decomposition e. Branchwidth ≤ diameter ≠ 1 f. Low-diameter slicing

From  Jeff Erickson 18 plays 0  

24. Maximum flows in surface maps

a. 1-chains = pseudoflows, circulations b. 2-chains = face potentials = Alexander numberings, boundary circulations c. Real-homology d. cycles, cocycles, and homology annotations e. Duality between…

From  Jeff Erickson 25 plays 0  

23. Minimum cuts in surface maps

a. Even subgraphs, cycle space, edge cuts, and cut spaceb. Planar duality c. Boundary subgraphs d. Z2-homology e. Systems of cycles and cocycles f. Homology anotations g. Dual of minimum cut is…

From  Jeff Erickson 25 plays 0  

22. Shortest nontrivial cycles in surfaces

a. Planarization b. Contractible versus separating c. Thomassen's 3-path condition ⇒ O(n³) time d. Greedy tree-cotree decompositions e. Greedy (reduced) cut graph ⇒ O(n² log…

From  Jeff Erickson 43 plays 0  

21. Homotopy testing on surfaces

a. Modeling curves on surfaces as walks in maps b. Spur and face moves c. System of loops d. Contractible in surface = closed in universal cover e. Dehn's lemma f. Dehn's algorithm g.…

From  Jeff Erickson 50 plays 0  

20. Surface Classification

a. Kerékjártó-Rado theorem (Every surface supports a map.) b. Tree-cotree decompositions and systems of loops c. Detaching handles by contracting two-sided loops d.…

From  Jeff Erickson 29 plays 0  

19. Surface Maps

a. 2-manifolds b. Polygonal schemata c. Cellular embeddings and rotation systems d. Orientation and genus e. Band decompositions f. Reflection systems g. Deletion and contraction in reflection systems

From  Jeff Erickson 30 plays 0  

18. Faster minimum cuts and maximum flows

a. FR-Dijkstra summary b. O(n log log n) minimum cut overview c. Technical details d. Planar maximum flow history e. Venkatesan's duality between flows and shortest paths f. Parametric shortest…

From  Jeff Erickson 22 plays 0  

17. FR-Dijkstra and faster minimum cuts

a. Monge heap operations: Revealing columns and hiding rows b. Range minimum queries c. Monge heap implementation d. High-level overview of FR-Dijkstra e. Monge structure of nice r-divisions f.…

From  Jeff Erickson 27 plays 0  

16. Planar minimum cuts

a. Duality: Shortest essential cycle b. Crosses shortest path at most once c. Slicing into a shortest-path problem d. Easy algorithms: Brute force and MSSP e. Divide-and-conquer: O(n log k) time f.…

From  Jeff Erickson 23 plays 0  

15. Planar shortest paths

a. Dense distance graphs b. Improving Dijkstra to O(n log log n) time c. Repricing d. Nested dissection e. Monge arrays and SMAWK f. Planar distances are (almost) Monge) g. Shortest paths with…

From  Jeff Erickson 25 plays 0  

14. Planar separators

a. Tree separators b. Fundamental cycle separators c. BFS level separators d. Face-level cycles e. Short cycle separators f. Good r-divisions

From  Jeff Erickson 33 plays 0  

13. Multiple-source shortest paths

a. Problem statement b. Shortest paths and slacks c. Disk-tree lemma and compact output d. Red and blue vertices, active darts e. Dynamic forest data structures f. Summary: O(n) pivots, each in O(log…

From  Jeff Erickson 60 plays 0  

12. Tutte's spring embedding

a. Tutte drawings b. Physical intuition: energy minimization c. Halfplane lemma d. No degenerate vertex neighborhoods e. No degenerate faces

From  Jeff Erickson 46 plays 0  

11. Straight-line planar maps

a. Simple triangulation lemma b. Hole filling (Every pentagon is star-shaped) c. Vertex deletion d. Schnyder woods e. Grid embedding

From  Jeff Erickson 38 plays 0  

10. Deletion and contraction

a. Deletion and contraction in abstract graphs b. Spanning trees c. Planar duality: (Σ\e)* = Σ*/e* d. Implementing deletion and contraction in maps e. Cycle-cut duality f. Tree-cotree…

From  Jeff Erickson 48 plays 0  

9. Planar graphs and maps

a. What is a graph? (vertices and darts) b. Incidence list and incidence array data structures c. Planar maps: faces, shores, face degree d. Rotation systems e. Stereographic projection f. Planar map…

From  Jeff Erickson 55 plays 0  

8. Curve homotopy and curve invariants

a. Steinitz's contraction algorithm (spindle removal) b. Rotation number: Smiles minus frowns c. Rotation number: Initial winding and writhe d. Defect

From  Jeff Erickson 26 plays 0  

7. Unsigned Gauss codes

a. Winding numbers and Alexander numbering b. Gauss smoothing and Seifert decompositions c. Gauss' parity condition and the Nagy graph d. Dehn smoothing and Euler tours e. Tree-onion…

From  Jeff Erickson 43 plays 0  

6. Generic curves in the plane

a. Definitions: transverse intersection, generic curve (immersion) b. Isotopy c. Image graphs and their faces d. Homotopy moves e. Planarity: F = V+2 f. Gauss codes and Gauss diagrams g. Tracing…

From  Jeff Erickson 44 plays 0  

5. Shortest homotopic paths

a. Shortest paths in simple polygons b. Crossing sequences via triangulation c. Dual tree of a polygon triangulation d. The funnel algorithm e. Adding holes: Nothing changes! f. Universal cover:…

From  Jeff Erickson 42 plays 0  

4. Faster homotopy testing

a. Quadratic lower bound? b. Trapezoidal decomposition c. Bentley-Ottmann sweep-line algorithm d. Horizontal and vertical ranks e. Rectification f. Sliding brackets g. Overall time analysis

From  Jeff Erickson 51 plays 0