The Islamic University of Gaza Faculty of Engineering Civil Engineering Department
The Islamic University of Gaza Faculty of Engineering Civil Engineering Department
description
Transcript of The Islamic University of Gaza Faculty of Engineering Civil Engineering Department
![Page 1: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/1.jpg)
The Islamic University of Gaza
Faculty of Engineering
Civil Engineering Department
Numerical Analysis
ECIV 3306
Chapter 4
1
Truncation Errors and Taylor Series
![Page 2: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/2.jpg)
Introduction
Truncation errors
• Result when approximations are used to represent exact mathematical procedure
• For example:
2
![Page 3: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/3.jpg)
3
Taylor Series - Definition
• Mathematical Formulation used widely in numerical methods to express functions in an approximate fashion……. Taylor Series.
• It is of great value in the study of numerical methods.
• It provides means to predict a functional value at one point in terms of:
- the function value - its derivatives at another point
![Page 4: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/4.jpg)
Taylor’s Theorem
Where:
ii xxh 1
1)1(
)!1(
)(
n
n
n hn
fR
4
n
ni
nii
iiiR
n
hxfhxfhxfhxfxfxf
!
)(.......
!3
)(
!2
)('')()()(
)(3)3(2'
1
General Expression
Rn is the remainder term to account
for all terms from n+1 to infinity.
And is a value of x that lies somewhere between xi and xi+1
![Page 5: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/5.jpg)
Taylor’s Theorem
)()(1 ii
xfxf
!2
)('')()()(
2'
1
hxfhxfxfxf i
iii
hxfxfxf iii)()()( '
1
5
Zero- order approximation: only true if xi+1 and xi are very close to each other. First- order approximation: in form of a straight line
Second- order approximation:
Any smooth function can be approximated as a polynomial
![Page 6: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/6.jpg)
Taylor’s Theorem - Remainder Term
Remainder Term: What is ξ ?
h
Rf o)(' oii
Rxfxf
)()(1
6
If Zero- order approximation:
![Page 7: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/7.jpg)
Taylor Series - Example Use zero-order to fourth-order Taylor series expansions to
approximate the function. f(x)= -0.1x4 – 0.15x3 – 0.5x2 – 0.25x +1.2
From xi = 0 with h =1. Predict the function’s value at xi+1 =1.
Solution f(xi)= f(0)= 1.2 , f(xi+1)= f(1) = 0.2 ………exact solution
• Zero- order approx. (n=0) f(xi+1)=1.2
Et = 0.2 – 1.2 = -1.0
• First- order approx. (n=1) f(xi+1)= 0.95 f(x)= -0.4x3 – 0.45x2 – x – 0.25, f ’(0)= -0.25 f( xi+1)= 1.2- 0.25h = 0.95 Et = 0.2 - 0.95 = -0.75
)()(1 ii
xfxf
hxfxfxf iii)()()( '
1
7
![Page 8: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/8.jpg)
Taylor Series - Example• Second- order approximation (n=2) f(xi+1)= 0.45
f ’’(x) = -1.2 x2 – 0.9x -1 , f ’’(0)= -1
f( xi+1)= 1.2 - 0.25h - 0.5 h2 = 0.45
Et = 0.2 – 0.45 = -0.25
• Third-order approximation (n=3) f(xi+1)= 0.3
f( xi+1)= 1.2 - 0.25h - 0.5 h2 – 0.15h3 = 0.3
Et = 0.2 – 0.3 = -0.1
!2
)('')()()(
2'
1
hxfhxfxfxf i
iii
!3
)(
!2
)('')()()(
3(3)2'
1
hxfhxfhxfxfxf ii
iii
8
![Page 9: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/9.jpg)
Taylor Series - Example
• Fourth-order approximation (n = 4) f(xi+1)= 0.2
f( xi+1)= 1.2 - 0.25h - 0.5 h2 – 0.15h3 – 0.1h 4= 0.2
Et = 0.2 – 0.2 = 0
The remainder term (R4) = 0
because the fifth derivative of the fourth-order polynomial is zero.
!4
)(
!3
)(
!2
)('')()()(
4)4(3)3(2'
1
hxfhxfhxfhxfxfxf iii
iii
5)5(
4 !5
)(h
fR
9
![Page 10: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/10.jpg)
10
Approximation using Taylor Series Expansion
The nth-order Approximation
![Page 11: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/11.jpg)
Taylor Series
• In General, the n-th order Taylor Series will be exact for n-th order polynomial.
• For other differentiable and continuous functions, such as exponentials and sinusoids, a finite number of terms will not yield an exact estimate. Each additional term will contribute some improvement.
(see example 4.2)
11
![Page 12: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/12.jpg)
Example 4.2
12
![Page 13: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/13.jpg)
13
![Page 14: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/14.jpg)
Effect of non-linearity
14
![Page 15: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/15.jpg)
15
![Page 16: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/16.jpg)
16
![Page 17: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/17.jpg)
Taylor Series
• Truncation error is decreased by addition of terms to the Taylor series.
• If h is sufficiently small, only a few terms may be required to obtain an approximation close enough to the actual value for practical purposes.
17
![Page 18: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/18.jpg)
18
Effect of step size
![Page 19: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/19.jpg)
19
![Page 20: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/20.jpg)
20
![Page 21: The Islamic University of Gaza Faculty of Engineering Civil Engineering Department](https://reader037.fdocuments.us/reader037/viewer/2022102801/56814e02550346895dbb70c0/html5/thumbnails/21.jpg)
21