ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Numerical Integration
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Objectives
• The student should be able to
– Understand the need for numerica...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Need for Numerical Integration!
( )
6
11
01
2
1
3
1
23
1
1
0
231
0
2
=−


...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Interpolation!
• If we have a function that needs to be
integrated between tw...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Example
• To perform the
definite integration of
the function between
(x0 & x...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Example
• Performing the integration on the approximate
function:
( ) ( )∫∫ ...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Example
• Performing the integration on the approximate
function:





...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
The Trapezoidal Rule
( ) ( )
2
01
01
yy
xxI
+
−≈
( ) ( )
( ) ( )
2
2
12
12
01...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
General Trapezoidal Rule
• For all the points equally separated
(xi+1-xi=h)
•...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
In general






++≈ ∑
−
=
n
n
i
i yyy
h
I
1
1
0 2
2
Where n is the num...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Example
• Integrate
• Using the trapezoidal
rule
• Use 2 points and
compare w...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Solution
• Using 2 points (n=1),
h=(1-0)/(1)=1
• Substituting:
( )21
2
1
yyI ...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Solution
• Using 3 points (n=2),
h=(1-0)/(2)=0.5
• Substituting:
( )321 2
2
5...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Quadratic Interpolation
• If we get to interpolate a quadratic equation
betwe...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Integrating
( ) ( ) ( )( )1010
2
3021 xxxxxxbxxbbxf ++−+−+≈
( ) ( ) ( )( )∫∫ ...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
After substitutions and
manipulation!
( ) [ ]210 4
3
2
0
yyy
h
dxxf
x
x
++≈∫
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
For 4-Intervals
( ) [ ]23210 424
3
4
0
yyyyy
h
dxxf
x
x
++++≈∫
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
In General: Simpson’s Rule
( ) 





+++≈ ∑∑∫
−
=
−
=
n
n
i
i
n
i
i
x
x...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Example
• Integrate
• Using the Simpson
rule
• Use 3 points
∫=
1
0
2
dxxI
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Solution
• Using 3 points (n=2),
h=(1-0)/(2)=0.5
• Substituting:
• Which is t...
ENEM602 Spring 2007
Dr. Eng. Mohammad Tawfik
Homework #7
• Chapter 21, pp. 610-612, numbers:
21.1, 21.3, 21.5, 21.25, 21.2...
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08 numerical integration

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08 numerical integration

  1. 1. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Numerical Integration
  2. 2. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Objectives • The student should be able to – Understand the need for numerical integration – Derive the trapezoidal rule using linear interpolation – Apply the trapezoidal rule – Derive Simpson’s rule using parabolic interpolation – Apply Simpson’s rule
  3. 3. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Need for Numerical Integration! ( ) 6 11 01 2 1 3 1 23 1 1 0 231 0 2 =−      ++=       ++=++= ∫ x xx dxxxI ( ) 11 0 1 0 1 −−− −=−== ∫ eedxeI xx ∫ − = 1 0 2 dxeI x
  4. 4. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Interpolation! • If we have a function that needs to be integrated between two points • We may use an approximate form of the function to integrate! • Polynomials are always integrable • Why don’t we use a polynomial to approximate the function, then evaluate the integral
  5. 5. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Example • To perform the definite integration of the function between (x0 & x1), we may interpolate the function between the two points as a line. ( ) ( )0 01 01 0 xx xx yy yxf − − − +≈
  6. 6. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Example • Performing the integration on the approximate function: ( ) ( )∫∫       − − − +≈= 1 0 1 0 0 01 01 0 x x x x dxxx xx yy ydxxfI 1 0 0 2 01 01 0 2 x x xx x xx yy xyI               − − − +≈
  7. 7. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Example • Performing the integration on the approximate function:                 − − − +−                 − − − +≈ 00 2 0 01 01 0010 2 1 01 01 10 22 xx x xx yy xyxx x xx yy xyI ( ) ( ) 2 01 01 yy xxI + −≈ • Which is equivalent to the area of the trapezium!
  8. 8. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik The Trapezoidal Rule ( ) ( ) 2 01 01 yy xxI + −≈ ( ) ( ) ( ) ( ) 2 2 12 12 01 01 yy xx yy xxI + −+ + −≈ Integrating from x0 to x2:
  9. 9. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik General Trapezoidal Rule • For all the points equally separated (xi+1-xi=h) • We may write the equation of the previous slide: ( ) ( ) ( ) ( ) ( )321 23 23 12 12 2 2 22 yyy h yy xx yy xxI ++= + −+ + −≈
  10. 10. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik In general       ++≈ ∑ − = n n i i yyy h I 1 1 0 2 2 Where n is the number if intervals and h=total interval/n
  11. 11. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Example • Integrate • Using the trapezoidal rule • Use 2 points and compare with the result using 3 points ∫= 1 0 2 dxxI
  12. 12. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Solution • Using 2 points (n=1), h=(1-0)/(1)=1 • Substituting: ( )21 2 1 yyI +≈ ( ) 5.010 2 1 =+≈I
  13. 13. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Solution • Using 3 points (n=2), h=(1-0)/(2)=0.5 • Substituting: ( )321 2 2 5.0 yyyI ++≈ ( ) 375.0125.0*20 2 5.0 =++≈I
  14. 14. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Quadratic Interpolation • If we get to interpolate a quadratic equation between every neighboring 3 points, we may use Newton’s interpolation formula: ( ) ( ) ( )( )103021 xxxxbxxbbxf −−+−+≈ ( ) ( ) ( )( )1010 2 3021 xxxxxxbxxbbxf ++−+−+≈
  15. 15. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Integrating ( ) ( ) ( )( )1010 2 3021 xxxxxxbxxbbxf ++−+−+≈ ( ) ( ) ( )( )∫∫ ++−+−+≈ 2 0 2 0 1010 2 3021 x x x x dxxxxxxxbxxbbdxxf ( ) ( ) 2 0 2 0 10 2 10 3 30 2 21 232 x x x x xxx x xx x bxx x bxbdxxf             ++−+      −+≈∫
  16. 16. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik After substitutions and manipulation! ( ) [ ]210 4 3 2 0 yyy h dxxf x x ++≈∫
  17. 17. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik For 4-Intervals ( ) [ ]23210 424 3 4 0 yyyyy h dxxf x x ++++≈∫
  18. 18. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik In General: Simpson’s Rule ( )       +++≈ ∑∑∫ − = − = n n i i n i i x x yyyy h dxxf n 2 ,..4,2 1 ,..3,1 0 24 30 NOTE: the number of intervals HAS TO BE even
  19. 19. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Example • Integrate • Using the Simpson rule • Use 3 points ∫= 1 0 2 dxxI
  20. 20. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Solution • Using 3 points (n=2), h=(1-0)/(2)=0.5 • Substituting: • Which is the exact solution! ( )210 4 3 5.0 yyyI ++≈ ( ) 3 1 125.0*40 3 5.0 =++≈I
  21. 21. ENEM602 Spring 2007 Dr. Eng. Mohammad Tawfik Homework #7 • Chapter 21, pp. 610-612, numbers: 21.1, 21.3, 21.5, 21.25, 21.28. • Due date: Week 8-12 May 2005
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