Principal Curve Lin Binbin Oct. 16th
Prom PCA to Principal curve 1904 Spearman PCA 1983 Trevor Hastie Principal curve “Principal curve and surface”
What is principal curve? Continuous Middle …
What is principal curve? (Hastie and Stuetzle) HS principal curve 1. f does not intersect itself, 2. f has finite length inside any bounded subset of and 3. f is self-consistent, i.e.,
Projecting a points to a curve
HS principal algorithm
HS Result
Summary Measure middle-self consistent One dimensional structure of the manifold Bias Existence Uniqueness Convergence High dimensional generalization
Problem of principal curve No exact object function Theoretical foundation: differential manifold and Riemannian geometry
Kegl principal curve Length constrain Existence
Kegl principal curve Data fittingSmoothness Average curvatureAverage distance
Projection distribution
Result
Failure case
Local and global Top-down strategies – Start with straight line Bottom-up strategies – Start with local neighborhood
Principal oriented points(POPS) POCP: principal curve of oriented points
POPS(Delicado) Each point xOrthogonal vectorDefine a function And a vector b, we have a hyperplane Minimizing the total variance Fixed points of is called principal oriented points. x: center b: direction
LPC algorithm Local principal curve
Summary Theory High dimension