Mar 29, 2002 ------------ - Introduction to splines - piecewise polynomials that are "as smooth as possible" - Applications and contexts - draftsmen in 1800s (plastic and wood strips) - free-form curves in Microsoft Word - surface splines (e.g., automobile surfaces) - computer animation (in-betweening) - aesthetics (e.g., reversing a car) - Advantages of being piecewise - allows you to be local in your modeling - an interpolating polynomial oscillates widely as degree increases - recall f(x) = max(0,1-x) - Advantages of being a polynomial - have continuous derivatives of all orders! - Examples of piecewise polynomials - piecewise constant - piecewise linear - piecewise quadratic - piecewise cubic - Types of continuity - values only: C^0 - values and first derivatives: C^1 - " + second derivatives: C^2 - Definition of spline - piecewise polynomial of degree n - joined together at break points (called knots) - with (n-1) continuous derivatives - Why only (n-1)? - Usage of word spline varies widely from books - your book: first two conditions above are enough - other books: a C^2 piecewise cubic (very specific) - because human eye can't notice jumps in third derivative - we will use the above definition - Two types of splines - interpolating spline - approximating spline - Evaluating piecewise polynomials - linear search through entries - binary search - shifted power form (around left knot) is advantageous - Finding splines: piecewise linear - 2k unknowns (coefficients) - 2k conditions - Finding splines: piecewise quadratic - 3k coefficients - 2k + k - 1 = 3k-1 conditions (impose one more condition yourself, e.g., S'(t_0) = 0) - Started on Problem 7.1.7 from textbook Apr 1, 2002 ------------ - Revisiting the three conditons for splines - why are they necessary? - Completed Problem 7.1.7 - Cubic splines - two missing conditions here - many ways of cooking these up - Natural cubic splines: one specific way of cooking up - S''(t_0) = S''(t_n) = 0 Apr 3, 2002 ------------ - Algorithm for natural cubic splines - Tridiagonal system solution - formulating the system around second derivatives - solving it - finding piecewise polynomials from previous - Parametric splines Apr 5, 2002 ------------ - More working out problems from book - Example 2 - Problem 7.2.32 - Problem 7.2.26 - B-Splines - need for a basis Apr 8, 2002 ------------ - Introduction to B-Splines - B^0 splines - B^1 splines - Finding coefficients for B^0 and B^1 splines - just read off the values! - Recursive definition of B^1 splines - linear combination of two B^0 splines - Extending the analogy - Curves and surfaces using B-splines