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Single & Multi-step Methods for First Order Differential Equations

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Chapter 06.indd   135 5/31/2017   10:59:53 AM
Page 2


    
    
 
 
  
  
  
  
  
  
     
 
 
  
  
      
      
  
  
   
 
   
    
      
Chapter 06.indd   135 5/31/2017   10:59:53 AM
    
\ In general,
 y
n+1
 = y
n
 + hy
n
' + 
h
2
2!
 y
n
? +… will be the iterative formula.
Example
Given 
dy
dx
 = x - y
2
 with the initial condition y(0) = 1
Find y (0.1) using Taylor series method with step size 0.1.
Solution
 f (x, y) = x - y
2
x = 0.1, x
0
 = 0, y
0
 = 1, h = 0.1
y' = x - y
2
 ? y'(0) = x
0
 - y
0
2
 = - 1;
y? = 1 - 2yy' ? y?(0) = 1 - 2y
0
y
0
'
= 1 - 2 (1) (-1) = 3
y?' = -2yy? - 2(y')
2
? y?' (0) = -2 (1) (3) - 2 (-1)
2
= -6 - 2 = -8
By Taylor’ s formula,
 y (0.1) = y
1
 = y
0
 + hy ' (0) + 
h
2
2!
y? (0) + 
h
3
3!
y'? (0) + 
…
? y
1
 = 1 + (0.1) (-1) + 
(. )
!
()
(. )
!
()
01
2
3
01
3
8
23
+- + 
…
= 1 - 0.1 + 0.015 - 0.0013 + 
…
y
1
 = 0.9137.
Picard’s Method of Successive  
Approximation
Given the differential equation 
dy
dx
 = f (x, y) (1)
Integrate Eq. (1) from x
0
 to x, we get
dy fx ydx
x
x
x
x
=
? ?
(, )
0 0
 
?- =
?
yx yx fx ydx
x
x
() () (, )
0
0
 
?= +
?
yx yx fx ydx
x
x
() () (, )
0
0
 (2)
Put y = y
0
, we get the first approximation,
y
n
 = y
0
 + fx ydx
n
x
x
(, ).
-
?
1
0
Example 
Given 
dy
dx
 = 1 + xy and y (0) = 1. Evaluate y (0.1) by Picard’ s 
method upto three approximations.
Solution
f (x, y) = 1 + xy
x
0
 = 0, y
0
 = 1
The first approximation y
1
 = y
0
 + fx ydx
x
x
(, )
0
0
?
1 + 1
0
0
+
?
xy dx
x
x
 = 1 + 1
0
+
?
xdx
x
y
1
 = 1 + x + 
x
2
2
At x = 0.1, y
1
 = 1 + (0.1) + 
(. ) 01
2
2
 = 1.105
The second approximation y
2
,
= y
0
 + fx ydx
x
x
(, )
1
0
?
? y
2
 = 1 + 1
1
0
+
?
xy dx
x
? y
2
 = 1 + 11
2
2
0
++ +
?
?
?
?
?
?
?
?
?
?
?
?
?
xx
x
dx
x
 = 1 + 1
2
2
3
0
++ +
?
?
?
?
?
? ?
xx
x
dx
x
 = 1 + x
xx x
++ +
234
23 8
At x = 0.1, y
2
 = 1 + (0.1) + 
(. )( .) (. ) 01
2
01
3
01
8
234
++
y(0.1) = 1.10534
The third approximation y
3
 = y
0
 + fx ydx
x
x
(, )
2
0
?
·
? y
3
 = 1 + () . 1
2
0
+
?
xy dx
x
1 + 11
23 8
234
0
++ ++ +
?
?
?
?
?
?
?
?
?
?
?
? ?
xx
xx x
dx
x
1 + 1
23 8
2
34 5
0
++ ++ +
?
?
?
?
?
? ?
xx
xx x
dx
x
= 1 + x + 
x
2
2
 + 
x
3
3
 + 
xx x
45 6
81548
++
At x = 0.1,
 y
3
 = 1 + (0.1) + 
(. )( .) (. )( .) (. ) 01
2
01
3
01
8
01
15
01
48
234 56
++ ++
 
   
(. )( .) (. )( .) (. ) 01
2
01
3
01
8
01
15
01
48
234 56
++ ++
=  1 + 0.1 + 0.005 + 0.0003 + 0.0000125 + 
0.0000006 + 0.00000002
y
3
 = 1.105313
Chapter 06.indd   136 5/31/2017   10:59:56 AM
Page 3


    
    
 
 
  
  
  
  
  
  
     
 
 
  
  
      
      
  
  
   
 
   
    
      
Chapter 06.indd   135 5/31/2017   10:59:53 AM
    
\ In general,
 y
n+1
 = y
n
 + hy
n
' + 
h
2
2!
 y
n
? +… will be the iterative formula.
Example
Given 
dy
dx
 = x - y
2
 with the initial condition y(0) = 1
Find y (0.1) using Taylor series method with step size 0.1.
Solution
 f (x, y) = x - y
2
x = 0.1, x
0
 = 0, y
0
 = 1, h = 0.1
y' = x - y
2
 ? y'(0) = x
0
 - y
0
2
 = - 1;
y? = 1 - 2yy' ? y?(0) = 1 - 2y
0
y
0
'
= 1 - 2 (1) (-1) = 3
y?' = -2yy? - 2(y')
2
? y?' (0) = -2 (1) (3) - 2 (-1)
2
= -6 - 2 = -8
By Taylor’ s formula,
 y (0.1) = y
1
 = y
0
 + hy ' (0) + 
h
2
2!
y? (0) + 
h
3
3!
y'? (0) + 
…
? y
1
 = 1 + (0.1) (-1) + 
(. )
!
()
(. )
!
()
01
2
3
01
3
8
23
+- + 
…
= 1 - 0.1 + 0.015 - 0.0013 + 
…
y
1
 = 0.9137.
Picard’s Method of Successive  
Approximation
Given the differential equation 
dy
dx
 = f (x, y) (1)
Integrate Eq. (1) from x
0
 to x, we get
dy fx ydx
x
x
x
x
=
? ?
(, )
0 0
 
?- =
?
yx yx fx ydx
x
x
() () (, )
0
0
 
?= +
?
yx yx fx ydx
x
x
() () (, )
0
0
 (2)
Put y = y
0
, we get the first approximation,
y
n
 = y
0
 + fx ydx
n
x
x
(, ).
-
?
1
0
Example 
Given 
dy
dx
 = 1 + xy and y (0) = 1. Evaluate y (0.1) by Picard’ s 
method upto three approximations.
Solution
f (x, y) = 1 + xy
x
0
 = 0, y
0
 = 1
The first approximation y
1
 = y
0
 + fx ydx
x
x
(, )
0
0
?
1 + 1
0
0
+
?
xy dx
x
x
 = 1 + 1
0
+
?
xdx
x
y
1
 = 1 + x + 
x
2
2
At x = 0.1, y
1
 = 1 + (0.1) + 
(. ) 01
2
2
 = 1.105
The second approximation y
2
,
= y
0
 + fx ydx
x
x
(, )
1
0
?
? y
2
 = 1 + 1
1
0
+
?
xy dx
x
? y
2
 = 1 + 11
2
2
0
++ +
?
?
?
?
?
?
?
?
?
?
?
?
?
xx
x
dx
x
 = 1 + 1
2
2
3
0
++ +
?
?
?
?
?
? ?
xx
x
dx
x
 = 1 + x
xx x
++ +
234
23 8
At x = 0.1, y
2
 = 1 + (0.1) + 
(. )( .) (. ) 01
2
01
3
01
8
234
++
y(0.1) = 1.10534
The third approximation y
3
 = y
0
 + fx ydx
x
x
(, )
2
0
?
·
? y
3
 = 1 + () . 1
2
0
+
?
xy dx
x
1 + 11
23 8
234
0
++ ++ +
?
?
?
?
?
?
?
?
?
?
?
? ?
xx
xx x
dx
x
1 + 1
23 8
2
34 5
0
++ ++ +
?
?
?
?
?
? ?
xx
xx x
dx
x
= 1 + x + 
x
2
2
 + 
x
3
3
 + 
xx x
45 6
81548
++
At x = 0.1,
 y
3
 = 1 + (0.1) + 
(. )( .) (. )( .) (. ) 01
2
01
3
01
8
01
15
01
48
234 56
++ ++
 
   
(. )( .) (. )( .) (. ) 01
2
01
3
01
8
01
15
01
48
234 56
++ ++
=  1 + 0.1 + 0.005 + 0.0003 + 0.0000125 + 
0.0000006 + 0.00000002
y
3
 = 1.105313
Chapter 06.indd   136 5/31/2017   10:59:56 AM
    
Multi-step Methods
Euler’s Method
For the differential equation 
dy
dx
 = f (x, y) with initial condi-
tion y(x
0
) = y
0
, the Euler’ s iteration formula is
y
n
 = y
n-1
 + h f (x
n-1
, y
n-1
), n = 1, 2, 3,…
The process is very slow and to obtain accuracy, h must 
be very small, i.e., we have to divide [x
0
, x
n
] into a more 
number of subintervals of length ‘h’.
NOTE
Example
Solve 
dy
dx
yx
yx
=
-
+
, y (0) = 1, find y(0.5) by Euler’s method 
choosing h = 0.25.
Solution
f (x, y) = 
yx
yx
-
+
x
0
 = 0, y
0
 = 1, h = 0.25
Euler’ s iteration formula,
y
n
 = y
n-1
 + h f (x
n-1
, y
n-1
)
Put n = 1,
x
1
 = 0.25 ? y
1
 = y(0.25) = y
0
 + h f (x
0
, y
0
)
= 1 + (0.25) 
yx
yx
00
00
-
+
?
?
?
?
?
?
= 1 + (0.25) 
10
10
-
+
 = 1.25
Put n = 2
x
2
 = 0.5 ? y
2
 = y(0.5) = y
1
 + h f (x
1
, y
1
)
= (1.25) + (0.25) 
yx
yx
11
11
-
+
?
?
?
?
?
?
= 1.25 + (0.25) 
1250 25
1250 25
..
..
-
+
?
?
?
?
?
?
= 1.25 + 0.166666 = 1.4166
\ y(0.5) = 1.4166
Modified Euler’s Method
For the differential equation 
dy
dx
 = f (x, y) with initial condi-
tion y(x
0
) = y
0
, the Modified Euler’ s iteration formula is
y
r
(n)
 = y
r-1
 + 
h
2
 [  f (x
r -1
, y
r - 1
) + f (x
r
, y
r
n-1
)]
To find y
n
, we proceed to find the approximations y
n
(0)
, 
y
n
(1)
, y
n
(2)
 … until the two successive approximations are 
approximately equal.
y
n
(0)
 is found by Euler’ s method, i.e., yy hf x
nn n
()
(,
0
11
=+
--
 
y
n-1
)
NOTE
Example 
Find y for x = 0.1 using modified Euler’ s method for the dif-
ferential equation 
dy
dx
 = log(x + y) with y(0) = 1.
Solution
Given f (x, y) = log(x + y)
x
0
 = 0, y
0
 = 1, h = 0.1
To find y
1
, x
1
 = 0.1
y
1
(0)
 = y
0
 + h f (x
0
, y
0
)
= 1 + (0.1) log(0 + 1) = 1
y
1
(1)
 = y
0
 + 
h
2
 [f (x
0
, y
0
) + f (x
1
, y
1
(0)
)]
= y
0
 + 
h
2
[log (x
0
 + y
0
) + log (x
1
 + y
1
(0)
)]
= 1 + 
01
2
.
[log (0 + 1) + log(0.1 + 1)]
= 1 + 
01
2
.
[log 1 + log 1.1] = 1.0047
y
1
(2)
 = y
0
 + 
h
2
[  f (x
0
, y
0
) + f (x
1
, y
1
(1)
)]
= y
0
 + 
h
2
[log(0 + 1) + log(x
1
 + y
1
(1)
)]
= 1 + 
01
2
.
[log(0 + 1) + log(0.1 + 1.0047)] 
= 1.0049
y
1
(3)
 = y
0
 + 
h
2
[  f(x
0
, y
0
) + f(x
1
, y
1
(2)
)]
= 1 + 
01
2
.
[log(0 + 1) + log(0.1 + 1.0049)]
= 1.0049
\ y
1
 = 1.0049.
Runge–Kutta Methods
First Order Runge–Kutta Method
y
1
 = y
0
 + hy
0
1
 [same as Euler’ s method]
Second Order Runge–Kutta Method
The formula is y
1
 = y
0
 + 
1
2
 
(k
1
 + k
2
)
where k
1
 = h f (x
0
, y
0
) and k
2
 = h f (x
0
 + h, y
0
 + k
1
)
Third Order Runge-Kutta Method
The formula is y
1
 = y
0
 + 
1
6
(k
1
 + 4k
2
 + k
3
)
where k
1
 = h f (x
0
, y
0
)
Chapter 06.indd   137 5/31/2017   10:59:58 AM
Page 4


    
    
 
 
  
  
  
  
  
  
     
 
 
  
  
      
      
  
  
   
 
   
    
      
Chapter 06.indd   135 5/31/2017   10:59:53 AM
    
\ In general,
 y
n+1
 = y
n
 + hy
n
' + 
h
2
2!
 y
n
? +… will be the iterative formula.
Example
Given 
dy
dx
 = x - y
2
 with the initial condition y(0) = 1
Find y (0.1) using Taylor series method with step size 0.1.
Solution
 f (x, y) = x - y
2
x = 0.1, x
0
 = 0, y
0
 = 1, h = 0.1
y' = x - y
2
 ? y'(0) = x
0
 - y
0
2
 = - 1;
y? = 1 - 2yy' ? y?(0) = 1 - 2y
0
y
0
'
= 1 - 2 (1) (-1) = 3
y?' = -2yy? - 2(y')
2
? y?' (0) = -2 (1) (3) - 2 (-1)
2
= -6 - 2 = -8
By Taylor’ s formula,
 y (0.1) = y
1
 = y
0
 + hy ' (0) + 
h
2
2!
y? (0) + 
h
3
3!
y'? (0) + 
…
? y
1
 = 1 + (0.1) (-1) + 
(. )
!
()
(. )
!
()
01
2
3
01
3
8
23
+- + 
…
= 1 - 0.1 + 0.015 - 0.0013 + 
…
y
1
 = 0.9137.
Picard’s Method of Successive  
Approximation
Given the differential equation 
dy
dx
 = f (x, y) (1)
Integrate Eq. (1) from x
0
 to x, we get
dy fx ydx
x
x
x
x
=
? ?
(, )
0 0
 
?- =
?
yx yx fx ydx
x
x
() () (, )
0
0
 
?= +
?
yx yx fx ydx
x
x
() () (, )
0
0
 (2)
Put y = y
0
, we get the first approximation,
y
n
 = y
0
 + fx ydx
n
x
x
(, ).
-
?
1
0
Example 
Given 
dy
dx
 = 1 + xy and y (0) = 1. Evaluate y (0.1) by Picard’ s 
method upto three approximations.
Solution
f (x, y) = 1 + xy
x
0
 = 0, y
0
 = 1
The first approximation y
1
 = y
0
 + fx ydx
x
x
(, )
0
0
?
1 + 1
0
0
+
?
xy dx
x
x
 = 1 + 1
0
+
?
xdx
x
y
1
 = 1 + x + 
x
2
2
At x = 0.1, y
1
 = 1 + (0.1) + 
(. ) 01
2
2
 = 1.105
The second approximation y
2
,
= y
0
 + fx ydx
x
x
(, )
1
0
?
? y
2
 = 1 + 1
1
0
+
?
xy dx
x
? y
2
 = 1 + 11
2
2
0
++ +
?
?
?
?
?
?
?
?
?
?
?
?
?
xx
x
dx
x
 = 1 + 1
2
2
3
0
++ +
?
?
?
?
?
? ?
xx
x
dx
x
 = 1 + x
xx x
++ +
234
23 8
At x = 0.1, y
2
 = 1 + (0.1) + 
(. )( .) (. ) 01
2
01
3
01
8
234
++
y(0.1) = 1.10534
The third approximation y
3
 = y
0
 + fx ydx
x
x
(, )
2
0
?
·
? y
3
 = 1 + () . 1
2
0
+
?
xy dx
x
1 + 11
23 8
234
0
++ ++ +
?
?
?
?
?
?
?
?
?
?
?
? ?
xx
xx x
dx
x
1 + 1
23 8
2
34 5
0
++ ++ +
?
?
?
?
?
? ?
xx
xx x
dx
x
= 1 + x + 
x
2
2
 + 
x
3
3
 + 
xx x
45 6
81548
++
At x = 0.1,
 y
3
 = 1 + (0.1) + 
(. )( .) (. )( .) (. ) 01
2
01
3
01
8
01
15
01
48
234 56
++ ++
 
   
(. )( .) (. )( .) (. ) 01
2
01
3
01
8
01
15
01
48
234 56
++ ++
=  1 + 0.1 + 0.005 + 0.0003 + 0.0000125 + 
0.0000006 + 0.00000002
y
3
 = 1.105313
Chapter 06.indd   136 5/31/2017   10:59:56 AM
    
Multi-step Methods
Euler’s Method
For the differential equation 
dy
dx
 = f (x, y) with initial condi-
tion y(x
0
) = y
0
, the Euler’ s iteration formula is
y
n
 = y
n-1
 + h f (x
n-1
, y
n-1
), n = 1, 2, 3,…
The process is very slow and to obtain accuracy, h must 
be very small, i.e., we have to divide [x
0
, x
n
] into a more 
number of subintervals of length ‘h’.
NOTE
Example
Solve 
dy
dx
yx
yx
=
-
+
, y (0) = 1, find y(0.5) by Euler’s method 
choosing h = 0.25.
Solution
f (x, y) = 
yx
yx
-
+
x
0
 = 0, y
0
 = 1, h = 0.25
Euler’ s iteration formula,
y
n
 = y
n-1
 + h f (x
n-1
, y
n-1
)
Put n = 1,
x
1
 = 0.25 ? y
1
 = y(0.25) = y
0
 + h f (x
0
, y
0
)
= 1 + (0.25) 
yx
yx
00
00
-
+
?
?
?
?
?
?
= 1 + (0.25) 
10
10
-
+
 = 1.25
Put n = 2
x
2
 = 0.5 ? y
2
 = y(0.5) = y
1
 + h f (x
1
, y
1
)
= (1.25) + (0.25) 
yx
yx
11
11
-
+
?
?
?
?
?
?
= 1.25 + (0.25) 
1250 25
1250 25
..
..
-
+
?
?
?
?
?
?
= 1.25 + 0.166666 = 1.4166
\ y(0.5) = 1.4166
Modified Euler’s Method
For the differential equation 
dy
dx
 = f (x, y) with initial condi-
tion y(x
0
) = y
0
, the Modified Euler’ s iteration formula is
y
r
(n)
 = y
r-1
 + 
h
2
 [  f (x
r -1
, y
r - 1
) + f (x
r
, y
r
n-1
)]
To find y
n
, we proceed to find the approximations y
n
(0)
, 
y
n
(1)
, y
n
(2)
 … until the two successive approximations are 
approximately equal.
y
n
(0)
 is found by Euler’ s method, i.e., yy hf x
nn n
()
(,
0
11
=+
--
 
y
n-1
)
NOTE
Example 
Find y for x = 0.1 using modified Euler’ s method for the dif-
ferential equation 
dy
dx
 = log(x + y) with y(0) = 1.
Solution
Given f (x, y) = log(x + y)
x
0
 = 0, y
0
 = 1, h = 0.1
To find y
1
, x
1
 = 0.1
y
1
(0)
 = y
0
 + h f (x
0
, y
0
)
= 1 + (0.1) log(0 + 1) = 1
y
1
(1)
 = y
0
 + 
h
2
 [f (x
0
, y
0
) + f (x
1
, y
1
(0)
)]
= y
0
 + 
h
2
[log (x
0
 + y
0
) + log (x
1
 + y
1
(0)
)]
= 1 + 
01
2
.
[log (0 + 1) + log(0.1 + 1)]
= 1 + 
01
2
.
[log 1 + log 1.1] = 1.0047
y
1
(2)
 = y
0
 + 
h
2
[  f (x
0
, y
0
) + f (x
1
, y
1
(1)
)]
= y
0
 + 
h
2
[log(0 + 1) + log(x
1
 + y
1
(1)
)]
= 1 + 
01
2
.
[log(0 + 1) + log(0.1 + 1.0047)] 
= 1.0049
y
1
(3)
 = y
0
 + 
h
2
[  f(x
0
, y
0
) + f(x
1
, y
1
(2)
)]
= 1 + 
01
2
.
[log(0 + 1) + log(0.1 + 1.0049)]
= 1.0049
\ y
1
 = 1.0049.
Runge–Kutta Methods
First Order Runge–Kutta Method
y
1
 = y
0
 + hy
0
1
 [same as Euler’ s method]
Second Order Runge–Kutta Method
The formula is y
1
 = y
0
 + 
1
2
 
(k
1
 + k
2
)
where k
1
 = h f (x
0
, y
0
) and k
2
 = h f (x
0
 + h, y
0
 + k
1
)
Third Order Runge-Kutta Method
The formula is y
1
 = y
0
 + 
1
6
(k
1
 + 4k
2
 + k
3
)
where k
1
 = h f (x
0
, y
0
)
Chapter 06.indd   137 5/31/2017   10:59:58 AM
    
k
2
 = h f x
0
+
1
2
1
2
01
hy k , +
?
?
?
?
?
?
 and
k
3
 = h f (x
0
 + h, y
0
 + k') where k' = h f(x
0
 + h, y
0
 + k
1
).
Fourth Order Runge–Kutta Method
The formula is y
1
 = y
0
 + 
1
6
 (k
1
 + 2k
2
 + 2k
3
 + k
4
)
where k
1
 = h f (x
0
, y
0
)
k
2
 = h f x
0
+
1
2
1
2
01
hy k , +
?
?
?
?
?
?
k
3
 = h f x
0
+
1
2
1
2
02
hy k , +
?
?
?
?
?
?
and k
4
 = h f (x
0
 + h, y
0
 + k
3
)
Example 
Given 
dy
dx
 = x
2
 + y
2
, y (1) = 1.2. Find y(1.05) applying fourth 
order Runge–Kutta method, with h = 0.05.
Solution
 f (x, y) = x
2
 + y
2
, x
0
 = 1, y
0
 = 1.2, h = 0.05
\k
1
 = h f (x
0
, y
0
) = (0.05) [x
0
2
 + y
0
2
]
= (0.05) [1
2
 + (1.2)
2
] = 0.122
k
2
 = h f 
x
h
y
k
00
1
22
++
?
?
?
?
?
?
,
= (0.05) [f (x
0
 + 0.025, y
0
 + 0.061]
= (0.05) [f (1.025, 1.261)]
= (0.05) [(1.025)
2
 + (1.261)
2
] = 0.1320
k
3
 = h f 
x
h
y
k
00
2
22
++
?
?
?
?
?
?
,
= (0.05) f (1 + 0.025, 1.2 + 0.066)
= (0.05) f (1.025, 1.266)
=  (0.05) [(1.025)
2
 + (1.266)
2
] = 0.1326 and k
4
 = h 
f (x
0
 + h, y
0
 + k
3
)
= (0.05) f (1 + 0.05, 1.2 + 0.1326)
= (0.05) f (1.05, 1.3326)
= (0.05) [(1.05)
2
 + (1.3326)
2
] = 0.1439
\ y
1
 = y(1.05) = y
0
 + 
1
6
(k
1
 + 2k
2
 + 2k
3
 + k
4
)
=  1.2 + 
1
6
[0.122 + 2(0.1320) + 2(0.1326)  
+ 0.1439]
= 1.2 + 
1
6
[0.7951] = 1.3325
Predictor–Corrector Methods
Milne’s Predictor Formula
y
n
p
+1
= y
n-3
 + 
4
3
h
 
(2y
n-2
 - y
n-1
 + 2y
n
)
Milne’s Corrector Formula
y
n
c
+1
= y
n-1
 + 
h
3
 
[y
n-1
 + 4y
n
 + y
n+1
p
]
Adams–Bashforth Predictor Formula
y
n
p
+1
= y
n
 + 
h
24
[55y
n
 - 59y
n-1
 + 37y
n-2
 - 9y
n-3
]
Adams–Moulton Corrector Formula
y
n
c
+1
 = y
n
 + 
h
24
[9
1
y
n
p
+
+ 19y
n
 - 5y
n-1
 + y
n-2
]
          
    
    
    
      
    
    
       
    
    
  
   
 
    
    
Chapter 06.indd   138 5/31/2017   11:00:01 AM
Read More

FAQs on Single & Multi-step Methods for First Order Differential Equations

1. What's the difference between Euler's method and Runge-Kutta method for solving first order differential equations?
Ans. Euler's method uses a single slope calculation at each step, making it simple but less accurate, while Runge-Kutta methods (especially fourth-order) use multiple slope evaluations to achieve higher precision. Fourth-order Runge-Kutta is significantly more accurate for the same step size, though computationally more involved. Single-step methods like these don't require previous solution points beyond the current one.
2. Why do multi-step methods like Adams-Bashforth need starting values from single-step methods?
Ans. Multi-step methods rely on multiple previous solution points to calculate the next value, so they cannot start solving immediately. Single-step methods like Runge-Kutta generate the initial required values. Once enough starting values exist, multi-step methods become computationally efficient because they use previously calculated data rather than recalculating slopes at each iteration.
3. How do I know which numerical method to choose when solving differential equations in exams?
Ans. Choose based on required accuracy and computational cost: use Euler's method for quick approximations, fourth-order Runge-Kutta for balanced accuracy-speed, and Adams-Bashforth or Adams-Moulton methods for problems requiring multiple successive steps with stored data. Step size and problem constraints also influence selection. Refer to mind maps and comparison flashcards on EduRev to visualize method characteristics clearly.
4. What does step size mean and how does it affect the accuracy of numerical solutions to differential equations?
Ans. Step size (h) is the interval width between consecutive points in numerical integration. Smaller step sizes produce more accurate solutions by reducing truncation error, but increase computational work and round-off error accumulation. Larger step sizes speed calculations but introduce significant approximation errors. Balance is essential for effective numerical methods in solving first-order differential equations.
5. Can single-step methods like Runge-Kutta solve all types of first order differential equations?
Ans. Single-step methods work for most first-order differential equations solvable analytically, including linear and nonlinear types, but require equations in the form dy/dx = f(x,y). They struggle with stiff equations where solution changes rapidly. Multi-step predictor-corrector methods sometimes handle such cases better. Always verify the method's applicability before applying it to your specific equation.
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