1. Spline Interpolation Method
Major: All Engineering Majors
Authors: Autar Kaw, Jai Paul
Transforming Numerical Methods Education for STEM Undergraduates

2. Spline Method of Interpolation http://numericalmethods.eng.usf.edu

3. What is Interpolation ?
Given (x0,y0), (x1,y1), …… (xn,yn), find the value of ‘y’ at a value of ‘x’ that is not given.

4. Interpolants Evaluate Differentiate, and Integrate.
Polynomials are the most common choice of interpolants because they are easy to:
Evaluate
Differentiate, and
Integrate.

5. Why Splines ?

6. Why Splines ?
Figure : Higher order polynomial interpolation is a bad idea

7. Linear Interpolation

8. Linear Interpolation (contd)

9. Example
The upward velocity of a rocket is given as a function of time in Table 1. Find the velocity at t=16 seconds using linear splines.
Table Velocity as a
function of time
(s)
(m/s) 10
227.04 15
362.78 20
517.35
22.5
602.97 30
901.67
Figure. Velocity vs. time data
for the rocket example

10. Linear Interpolation

11. Quadratic Interpolation

12. Quadratic Interpolation (contd)

13. Quadratic Splines (contd)

14. Quadratic Splines (contd)

15. Quadratic Splines (contd)

16. Quadratic Spline Interpolation Part 1 of 2 http://numericalmethods.eng.usf.edu

17. Quadratic Spline Example
The upward velocity of a rocket is given as a function of time. Using quadratic splines
Find the velocity at t=16 seconds
Find the acceleration at t=16 seconds
Find the distance covered between t=11 and t=16 seconds t
v(t) s
m/s 10
227.04 15
362.78 20
517.35
22.5
602.97 30
901.67

18. Data and Plot t v(t) s m/s 10 227.04 15 362.78 20 517.35 22.5 602.9710
227.04 15
362.78 20
517.35
22.5
602.97 30
901.67 18

19. Solution
Let us set up the equations

20. Each Spline Goes Through Two Consecutive Data Points

21. Each Spline Goes Through Two Consecutive Data Points
v(t) s
m/s 10
227.04 15
362.78 20
517.35
22.5
602.97 30
901.67

22. Derivatives are Continuous at Interior Data Points

23. Derivatives are continuous at Interior Data Points
At t=10
At t=15
At t=20
At t=22.5

24. Last Equation

25. Final Set of Equations

26. Coefficients of Splineai bi ci 1
22.704 2
0.8888
4.928
88.88 3
35.66 4
1.6048
554.55 5
28.86

27. END

28. Quadratic Spline Interpolation Part 2 of 2 http://numericalmethods.eng.usf.edu28

29. Final Solution

30. Velocity at a Particular Point
a) Velocity at t=16

31. Acceleration from Velocity Profile
b) Acceleration at t=16

32. Acceleration from Velocity Profile
The quadratic spline valid at t=16 is given by ,

33. Distance from Velocity Profile
c) Find the distance covered by the rocket from t=11s to t=16s. 33

34. Distance from Velocity Profile

35. Additional Resources
For all resources on this topic such as digital audiovisual lectures, primers, textbook chapters, multiple-choice tests, worksheets in MATLAB, MATHEMATICA, MathCad and MAPLE, blogs, related physical problems, please visit

36. END