1. Obstructions to Compatible Extensions of Mappings Duke University Joint with John Harer Jose Perea

2. June 1994 Monday (05/26/2014)

3. June 1994 Incremental ‘s Monday (05/26/2014)

4. June 1994 Incremental ‘s Monday (05/26/2014)

5. June 1994 Incremental ‘s 2002 Topological Persistence Monday (05/26/2014)

6. June 1994 Incremental ‘s 2002 Topological Persistence 2005 Computing P.H. Monday (05/26/2014)

7. June 1994 Incremental ‘s 2002 Topological Persistence 2005 Computing P.H. 2008 Extended Persistence Monday (05/26/2014)

8. June 1994 Incremental ‘s 2002 Topological Persistence 2005 Computing P.H. 2008 Extended Persistence 2009 Zig-Zag Persistence … Monday (05/26/2014)

9. June 1994Monday (05/26/2014) Incremental ‘s 2002 Topological Persistence 2005 Computing P.H. 2008 Extended Persistence 2009 Zig-Zag Persistence

11. What have we learned? Study the whole multi-scale object at once Is not directionality, but compatible choices … …

12. For Point-cloud data: 1.Encode multi-scale information in a filtration-like object 2.Make compatible choices across scales 3.Rank significance of such choices

13. To leverage the power of the relative-lifting paradigm and the language of obstruction theory The Goal:

14. To leverage the power of the relative-lifting paradigm and the language of obstruction theory The Goal: For data analysis!

15. Why do we care?

16. Useful concepts/invariants can be interpreted this way: 1.The retraction problem: 2.Extending sections: 3.Characteristic classes.

17. Back to Point-clouds: Model fitting

18. Example (model fitting): (3-circle model) (Klein bottle model) Mumford Data

19. Model fitting Only birth-like events

20. Local to global Example: Compatible extensions of sections

21. Local to global Only death-like events

22. Local to global Model fitting

23. Combine the two: The compatible-extension problem

24. How do we set it up?

25. Definition : The diagram Extends compatibly, if there exist extensions of the so that.

26. For instance :

27. Let be the tangent bundle over, and fix classifying maps If then, where Thus, Extend separately but not compatibly

28. Let be the tangent bundle over, and fix classifying maps If then, where Thus, Extend separately but not compatibly

29. Let be the tangent bundle over, and fix classifying maps If then, where Thus, Extend separately but not compatibly

30. Let be the tangent bundle over, and fix classifying maps If then, where Thus, Extend separately but not compatibly

31. Observation: Relative lifting problem up to homotopy rel Compatible extension problem

32. How do we solve it?

33. Solving the classic extension problem: The set-up Assume Want

34. Solving the classic extension problem: The set-up Assume Want

35. Solving the classic extension problem: The set-up Assume Want

36. Solving the classic extension problem: Assume Want The obstruction cocycle

37. is a cocycle, and if and only if extends. Moreover, if for some then there exists a map so that on, and Theorem

38. is a cocycle, and if and only if extends. Moreover, if for some then there exists a map so that on, and Theorem

39. Solving the compatible extension problem: The set-up Assume

42. Let for some. Then is a cocycle, which is zero if and only if Theorem I (Perea, Harer)

43. Theorem II (Perea, Harer) Let. If for, then and extend compatibly.

44. The upshot: Once we fix so that, then parametrizes the redefinitions of that extend. Moreover, if a pair, satisfies then the redefinitions of and via and, extend compatibly.

45. The upshot: Once we fix so that, then parametrizes the redefinitions of that extend. Moreover, if a pair, satisfies then the redefinitions of and via and, extend compatibly.

46. Putting everything together

48. … … … … …

49. Example

56. Can we actually compute this thing?

58. * Some times

60. Coming soon: Applications to database consistency Topological model fitting Bargaining/consensus in social networks

61. Thanks!!