1 INTERPOLASI

Direct Method of Interpolation

3 What is Interpolation ? Given (x 0,y 0 ), (x 1,y 1 ), …… (x n,y n ), find the value of ‘y’ at a value of ‘x’ that is not given. Figure 1 Interpolation of discrete.

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

5 Direct Method Given ‘n+1’ data points (x 0,y 0 ), (x 1,y 1 ),………….. (x n,y n ), pass a polynomial of order ‘n’ through the data as given below: where a 0, a 1,………………. a n are real constants. Set up ‘n+1’ equations to find ‘n+1’ constants. To find the value ‘y’ at a given value of ‘x’, simply substitute the value of ‘x’ in the above polynomial.

6 Example 1 The upward velocity of a rocket is given as a function of time in Table 1. Find the velocity at t=16 seconds using the direct method for linear interpolation Table 1 Velocity as a function of time. Figure 2 Velocity vs. time data for the rocket example

7 Linear Interpolation Solving the above two equations gives, Hence Figure 3 Linear interpolation.

8 Example 2 The upward velocity of a rocket is given as a function of time in Table 2. Find the velocity at t=16 seconds using the direct method for quadratic interpolation Table 2 Velocity as a function of time. Figure 5 Velocity vs. time data for the rocket example

9 Quadratic Interpolation Solving the above three equations gives Quadratic Interpolation Figure 6 Quadratic interpolation.

10 Quadratic Interpolation (cont.) The absolute relative approximate error obtained between the results from the first and second order polynomial is

11 Example 3 The upward velocity of a rocket is given as a function of time in Table 3. Find the velocity at t=16 seconds using the direct method for cubic interpolation Table 3 Velocity as a function of time. Figure 6 Velocity vs. time data for the rocket example

12 Cubic Interpolation Figure 7 Cubic interpolation.

13 Cubic Interpolation (contd) The absolute percentage relative approximate error between second and third order polynomial is

14 Comparison Table Table 4 Comparison of different orders of the polynomial.

15 Distance from Velocity Profile Find the distance covered by the rocket from t=11s to t=16s ?

16 Acceleration from Velocity Profile Find the acceleration of the rocket at t=16s given that

Lagrange Method of Interpolation

18 What is Interpolation ? Given (x 0,y 0 ), (x 1,y 1 ), …… (x n,y n ), find the value of ‘y’ at a value of ‘x’ that is not given.

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

20 Lagrangian Interpolation

21 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 the Lagrangian method for linear interpolation. Table Velocity as a function of time Figure. Velocity vs. time data for the rocket example (s) (m/s)

22 Linear Interpolation

23 Linear Interpolation (contd)

24 Quadratic Interpolation

25 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 the Lagrangian method for quadratic interpolation. Table Velocity as a function of time Figure. Velocity vs. time data for the rocket example (s) (m/s)

26 Quadratic Interpolation (contd)

27 Quadratic Interpolation (contd) The absolute relative approximate error obtained between the results from the first and second order polynomial is

28 Cubic Interpolation

29 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 the Lagrangian method for cubic interpolation. Table Velocity as a function of time Figure. Velocity vs. time data for the rocket example (s) (m/s)

30 Cubic Interpolation (contd)

31 Cubic Interpolation (contd) The absolute relative approximate error obtained between the results from the first and second order polynomial is

32 Comparison Table Order of Polynomial 123 v(t=16) m/s Absolute Relative Approximate Error % %

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

34 Acceleration from Velocity Profile, Find the acceleration of the rocket at t=16s given that

Newton’s Divided Difference Method of Interpolation

36 What is Interpolation ? Given (x 0,y 0 ), (x 1,y 1 ), …… (x n,y n ), find the value of ‘y’ at a value of ‘x’ that is not given.

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

38 Newton’s Divided Difference Method Linear interpolation: Given pass a linear interpolant through the data where

39 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 the Newton Divided Difference method for linear interpolation. Table. Velocity as a function of time Figure. Velocity vs. time data for the rocket example

40 Linear Interpolation

41 Linear Interpolation (contd)

42 Quadratic Interpolation

43 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 the Newton Divided Difference method for quadratic interpolation. Table. Velocity as a function of time Figure. Velocity vs. time data for the rocket example

44 Quadratic Interpolation (contd)

45 Quadratic Interpolation (contd)

46 Quadratic Interpolation (contd)

47 General Form where Rewriting

48 General Form

49 General form

50 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 the Newton Divided Difference method for cubic interpolation. Table. Velocity as a function of time Figure. Velocity vs. time data for the rocket example

51 Example The velocity profile is chosen as we need to choose four data points that are closest to

52 Example

53 Example

54 Comparison Table

55 Distance from Velocity Profile Find the distance covered by the rocket from t=11s to t=16s ?

56 Acceleration from Velocity Profile Find the acceleration of the rocket at t=16s given that