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Page 1
?= +
- ?
?
?
+
-+
+
?
?
?
dy
dx h
y
p
y
pp
y
12 1
2
36 2
3
0
2
0
2
3
0
??
?
()
!
()
!
?
?
?
?
?
?
?
dy
dx
at x = x
0
=? -? +? -? +?
?
?
?
?
?
?
11
2
1
3
1
4
1
5
0
2
0
3
0
4
0
5
0
h
yy yy …
(
\ At i = x
0
; p = 0)
And
dy
dx
d
dx
dy
dx
d
dp
dy
dx
dp
dx h
2
2
1
=
?
?
?
?
?
?
=
?
?
?
?
?
?
=
?? ?
2
0
3
0
2
4
0
66
3
12 36 22
4
1
y
p
y
pp
y
h
+
-
+
-+ ?
?
?
?
?
?
!!
dy
dx h
y
p
y
pp
y
2
2
2
0
3
0
2
4
0
16 6
3
12 36 22
1
2
?
?
?
?
?
?
=? +
-
?+
-+ ?
?
?
?
?
?
?
!!
dy
dx
xx
2
2
0
?
?
?
?
?
?
= at
=? -? +? -? +
?
?
?
?
?
?
111
12
5
6
2
2
0
3
0
4
0
5
0
h
yy yy
\ By using Newton’ s forward interpolation formula,
the first and second derivatives of y = f (x) at x = x
0
are
given by
dy
dx
xx
?
?
?
?
?
?
=
0
=? -? +? -? +?
?
?
?
?
?
?
11
2
1
3
1
4
1
5
0
2
0
3
0
4
0
5
0
h
yy yy y…
and
dy
dx h
yy yy
xx
2
22
2
0
3
0
4
0
5
0
0
111
12
5
6
?
?
?
?
?
?
=? -? +? -? +
?
?
?
?
?
?
=
…
2. Derivatives using newton’s backward difference
interpolation formula: We know that the Newton’s
backward difference interpolation formula is y = y
n
+
p? y
n
+
pp ()
!
+1
2
?
2
y
n
+
pp p ()()
!
++ 12
3
+ ?
3
y
n
…
Differentiating on both sides wrt p,
dy
dx
y
p
y
pp
y
nn n
=? +
+
?+
++
?+
21
2
36 2
3
2
2
3
!
As p
xx
h
dp
dx h
n
=
-
=
1
Chapter 06.indd 131 5/31/2017 10:59:42 AM
Page 2
?= +
- ?
?
?
+
-+
+
?
?
?
dy
dx h
y
p
y
pp
y
12 1
2
36 2
3
0
2
0
2
3
0
??
?
()
!
()
!
?
?
?
?
?
?
?
dy
dx
at x = x
0
=? -? +? -? +?
?
?
?
?
?
?
11
2
1
3
1
4
1
5
0
2
0
3
0
4
0
5
0
h
yy yy …
(
\ At i = x
0
; p = 0)
And
dy
dx
d
dx
dy
dx
d
dp
dy
dx
dp
dx h
2
2
1
=
?
?
?
?
?
?
=
?
?
?
?
?
?
=
?? ?
2
0
3
0
2
4
0
66
3
12 36 22
4
1
y
p
y
pp
y
h
+
-
+
-+ ?
?
?
?
?
?
!!
dy
dx h
y
p
y
pp
y
2
2
2
0
3
0
2
4
0
16 6
3
12 36 22
1
2
?
?
?
?
?
?
=? +
-
?+
-+ ?
?
?
?
?
?
?
!!
dy
dx
xx
2
2
0
?
?
?
?
?
?
= at
=? -? +? -? +
?
?
?
?
?
?
111
12
5
6
2
2
0
3
0
4
0
5
0
h
yy yy
\ By using Newton’ s forward interpolation formula,
the first and second derivatives of y = f (x) at x = x
0
are
given by
dy
dx
xx
?
?
?
?
?
?
=
0
=? -? +? -? +?
?
?
?
?
?
?
11
2
1
3
1
4
1
5
0
2
0
3
0
4
0
5
0
h
yy yy y…
and
dy
dx h
yy yy
xx
2
22
2
0
3
0
4
0
5
0
0
111
12
5
6
?
?
?
?
?
?
=? -? +? -? +
?
?
?
?
?
?
=
…
2. Derivatives using newton’s backward difference
interpolation formula: We know that the Newton’s
backward difference interpolation formula is y = y
n
+
p? y
n
+
pp ()
!
+1
2
?
2
y
n
+
pp p ()()
!
++ 12
3
+ ?
3
y
n
…
Differentiating on both sides wrt p,
dy
dx
y
p
y
pp
y
nn n
=? +
+
?+
++
?+
21
2
36 2
3
2
2
3
!
As p
xx
h
dp
dx h
n
=
-
=
1
Chapter 06.indd 131 5/31/2017 10:59:42 AM
?=
dy
dx
dy
dp
dp
dx
=? +
+
?+
++
?+
?
?
?
?
?
?
y
p
y
pp
y
h
nn n
21
2
36 2
3
1
2
2
3
!!
?= ?+
+
?+
++ ?
?
?
?+
?
?
?
dy
dx h
y
p
y
pp
y
nn
n
12 1
2
36 2
3
2
2
3
!!
dy
dx
xx
n
?
?
?
?
?
?
=
=? +? +? +? +? +
?
?
?
?
?
?
11
2
1
3
1
4
1
5
23 45
h
yy yy y
nn nn n
...
(
\ At x = x
n
; p = 0)
And
dy
dx
d
dx
dy
dx
d
dp
dy
dx
dp
dx
2
2
=
?
?
?
?
?
?
=
?
?
?
?
?
?
=? +
+
?+
++ ?
?
?
?+
?
?
?
16 6
3
12 36 22
4
1
23
2
4
h
y
p
y
pp
y
h
nn
n
!!
?=
dy
dx h
2
22
1
?+
+
?+
++
?+
?
?
?
?
?
?
23
2
4
66
3
12 36 22
4
y
p
y
pp
y
nn n
!!
?
?
?
?
?
?
?
=? +? +? +?
?
?
?
?
?
?
=
dy
dx h
yy yy
xx
nn nn
n
2
22
23 45
111
12
5
6
\ By using Newton’s backward difference
interpolation formula, the first and second derivatives
of y = f (x) at x = x
n
are given by
dy
dx
xx
n
?
?
?
?
?
?
=
=? +? +? +? +? +
?
?
?
?
?
?
11
2
1
3
1
4
1
5
23 45
h
yy yy y
nn nn n
and
dy
dx
xx
n
2
2
?
?
?
?
?
?
=
=? +? +? +? +
?
?
?
?
?
?
111
12
5
6
2
23 45
h
yy yy
nn nn
Example
Using the values of a function y = f (x) given in the following
table, find the first two derivatives of f (x) at x = 7.
x 2 3 4 5 6 7
y = f(x) 4 8 15 27 36 42
Solution
As we have to find the first two derivatives of y = f (x) at x
= 7, (end point of the given data), we use the derivatives’
formulae obtained from Newton’s backward interpolation
formula.
The backward difference table for the given data is
X y = f(x) Dy D 2
y D 3
y D 4
y D 5
y
2
3
4
5
6
7
4
8
15
27
36
42
4
7
12
9
6
3
5
-3
-3
-2
-8
0
6
8
2
By Newton’s backward interpolation formula, we have
dy
dx
xx
n
?
?
?
?
?
?
==7
=? +? +? +? +?
?
?
?
?
?
?
11
2
1
3
1
5
23 45
h
yy yy y
nn nn n
=+ ×- +× +× +×
?
?
?
?
?
?
==
1
1
6
1
2
3
1
3
0
1
4
8
1
5
2
69
10
69 () .
And
dy
dx
xx
n
2
2
7
?
?
?
?
?
?
==
=? +? ++?+ ?
?
?
?
?
?
?
111
12
5
6
2
23 45
h
yy yy
nn nn
=- ++ ×+ ×
?
?
?
?
?
?
=
1
1
30
11
12
8
5
6
26
2
.
Example
Find the first derivative at x = 6 for a function y = f (x) with
the following data.
x 5 7 10 11 13
y = f(x) 100 294 900 1210 2028
Solution
As the given values of x are not equally spaced, to find the
first derivative of f(x), we will make use of the Newton’s
divided difference interpolation formula, which is given by
y = f(x) = f(x
0
) + (x - x
0
) [x
0
, x
1
] + (x - x
0
)(x - x
1
) [x
0
, x
1
, x
2
] +
(x - x
0
)(x - x
1
)(x - x
2
) [x
0
, x
1
, x
2
x
3
] + (x - x
0
)(x - x
1
)(x - x
2
)
(x - x
3
)][x
0
, x
1
, x
2
, x
3
, x
4
] +
…
(1)
The divided differences of various orders for the given data
can be represented as shown below.
Chapter 06.indd 132 5/31/2017 10:59:45 AM
Page 3
?= +
- ?
?
?
+
-+
+
?
?
?
dy
dx h
y
p
y
pp
y
12 1
2
36 2
3
0
2
0
2
3
0
??
?
()
!
()
!
?
?
?
?
?
?
?
dy
dx
at x = x
0
=? -? +? -? +?
?
?
?
?
?
?
11
2
1
3
1
4
1
5
0
2
0
3
0
4
0
5
0
h
yy yy …
(
\ At i = x
0
; p = 0)
And
dy
dx
d
dx
dy
dx
d
dp
dy
dx
dp
dx h
2
2
1
=
?
?
?
?
?
?
=
?
?
?
?
?
?
=
?? ?
2
0
3
0
2
4
0
66
3
12 36 22
4
1
y
p
y
pp
y
h
+
-
+
-+ ?
?
?
?
?
?
!!
dy
dx h
y
p
y
pp
y
2
2
2
0
3
0
2
4
0
16 6
3
12 36 22
1
2
?
?
?
?
?
?
=? +
-
?+
-+ ?
?
?
?
?
?
?
!!
dy
dx
xx
2
2
0
?
?
?
?
?
?
= at
=? -? +? -? +
?
?
?
?
?
?
111
12
5
6
2
2
0
3
0
4
0
5
0
h
yy yy
\ By using Newton’ s forward interpolation formula,
the first and second derivatives of y = f (x) at x = x
0
are
given by
dy
dx
xx
?
?
?
?
?
?
=
0
=? -? +? -? +?
?
?
?
?
?
?
11
2
1
3
1
4
1
5
0
2
0
3
0
4
0
5
0
h
yy yy y…
and
dy
dx h
yy yy
xx
2
22
2
0
3
0
4
0
5
0
0
111
12
5
6
?
?
?
?
?
?
=? -? +? -? +
?
?
?
?
?
?
=
…
2. Derivatives using newton’s backward difference
interpolation formula: We know that the Newton’s
backward difference interpolation formula is y = y
n
+
p? y
n
+
pp ()
!
+1
2
?
2
y
n
+
pp p ()()
!
++ 12
3
+ ?
3
y
n
…
Differentiating on both sides wrt p,
dy
dx
y
p
y
pp
y
nn n
=? +
+
?+
++
?+
21
2
36 2
3
2
2
3
!
As p
xx
h
dp
dx h
n
=
-
=
1
Chapter 06.indd 131 5/31/2017 10:59:42 AM
?=
dy
dx
dy
dp
dp
dx
=? +
+
?+
++
?+
?
?
?
?
?
?
y
p
y
pp
y
h
nn n
21
2
36 2
3
1
2
2
3
!!
?= ?+
+
?+
++ ?
?
?
?+
?
?
?
dy
dx h
y
p
y
pp
y
nn
n
12 1
2
36 2
3
2
2
3
!!
dy
dx
xx
n
?
?
?
?
?
?
=
=? +? +? +? +? +
?
?
?
?
?
?
11
2
1
3
1
4
1
5
23 45
h
yy yy y
nn nn n
...
(
\ At x = x
n
; p = 0)
And
dy
dx
d
dx
dy
dx
d
dp
dy
dx
dp
dx
2
2
=
?
?
?
?
?
?
=
?
?
?
?
?
?
=? +
+
?+
++ ?
?
?
?+
?
?
?
16 6
3
12 36 22
4
1
23
2
4
h
y
p
y
pp
y
h
nn
n
!!
?=
dy
dx h
2
22
1
?+
+
?+
++
?+
?
?
?
?
?
?
23
2
4
66
3
12 36 22
4
y
p
y
pp
y
nn n
!!
?
?
?
?
?
?
?
=? +? +? +?
?
?
?
?
?
?
=
dy
dx h
yy yy
xx
nn nn
n
2
22
23 45
111
12
5
6
\ By using Newton’s backward difference
interpolation formula, the first and second derivatives
of y = f (x) at x = x
n
are given by
dy
dx
xx
n
?
?
?
?
?
?
=
=? +? +? +? +? +
?
?
?
?
?
?
11
2
1
3
1
4
1
5
23 45
h
yy yy y
nn nn n
and
dy
dx
xx
n
2
2
?
?
?
?
?
?
=
=? +? +? +? +
?
?
?
?
?
?
111
12
5
6
2
23 45
h
yy yy
nn nn
Example
Using the values of a function y = f (x) given in the following
table, find the first two derivatives of f (x) at x = 7.
x 2 3 4 5 6 7
y = f(x) 4 8 15 27 36 42
Solution
As we have to find the first two derivatives of y = f (x) at x
= 7, (end point of the given data), we use the derivatives’
formulae obtained from Newton’s backward interpolation
formula.
The backward difference table for the given data is
X y = f(x) Dy D 2
y D 3
y D 4
y D 5
y
2
3
4
5
6
7
4
8
15
27
36
42
4
7
12
9
6
3
5
-3
-3
-2
-8
0
6
8
2
By Newton’s backward interpolation formula, we have
dy
dx
xx
n
?
?
?
?
?
?
==7
=? +? +? +? +?
?
?
?
?
?
?
11
2
1
3
1
5
23 45
h
yy yy y
nn nn n
=+ ×- +× +× +×
?
?
?
?
?
?
==
1
1
6
1
2
3
1
3
0
1
4
8
1
5
2
69
10
69 () .
And
dy
dx
xx
n
2
2
7
?
?
?
?
?
?
==
=? +? ++?+ ?
?
?
?
?
?
?
111
12
5
6
2
23 45
h
yy yy
nn nn
=- ++ ×+ ×
?
?
?
?
?
?
=
1
1
30
11
12
8
5
6
26
2
.
Example
Find the first derivative at x = 6 for a function y = f (x) with
the following data.
x 5 7 10 11 13
y = f(x) 100 294 900 1210 2028
Solution
As the given values of x are not equally spaced, to find the
first derivative of f(x), we will make use of the Newton’s
divided difference interpolation formula, which is given by
y = f(x) = f(x
0
) + (x - x
0
) [x
0
, x
1
] + (x - x
0
)(x - x
1
) [x
0
, x
1
, x
2
] +
(x - x
0
)(x - x
1
)(x - x
2
) [x
0
, x
1
, x
2
x
3
] + (x - x
0
)(x - x
1
)(x - x
2
)
(x - x
3
)][x
0
, x
1
, x
2
, x
3
, x
4
] +
…
(1)
The divided differences of various orders for the given data
can be represented as shown below.
Chapter 06.indd 132 5/31/2017 10:59:45 AM
x y = f(x) First divided differences Second divided differences Third divided differences Fourth divided differences
5
7
10
11
13
100
294
900
1,210
2,028
294 100
75
97
-
-
=
900 294
10 7
202
-
-
=
1210 900
11 10
310
-
-
=
2028 1210
13 11
409
-
-
=
202 97
10 5
21
-
-
=
310 202
11 7
27
-
-
=
409 310
13 10
33
-
-
=
27 21
11 5
1
-
-
=
33 27
13 7
1
-
-
=
11
13 5
0
-
-
=
Substituting these in Eq. (1), we get
y = f(x) = 100 + (x - 5) × 97 + (x - 5)(x - 7) 21 + (x - 5) (x
- 7)(x - 10) × 1 + (x - 5)(x - 7)(x - 10)(x - 11) × 0
\ f (x) = 100 + 97(x - 5) + 21(x
2
- 12x + 35) + (x
3
- 22x
2
+ 155x - 350)
?=
dy
dx
97 + 21(2x - 12) + (3x
2
- 44x + 155)
?
?
?
?
?
?
?
=
dy
dx
x 6
= 97 + 21(2 × 6 - 12) + (3 × 6
2
- 44 × 6 +155)
= 97 + 0 + (- 1) = 96.
0
0
+
?
?
?
y
n
y
nn
0 0
23
+ +
- ?
?
(
Chapter 06.indd 133 5/31/2017 10:59:48 AM
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