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Abstract—In this paper, a numerical scheme, based on
fractional order generalized hat functions operational matrix of
integration for solving fractional integro-differential equations
of Bratu-type is presented. The operational matrix is used to
reduce the fractional integro-differential equation to a system of
algebraic equations. The error analysis of generalized hat
functions is also given. Numerical examples are provided to
demonstrate the validity and applicability of the method.
Moreover, comparing the methodology with the known
technique shows that our approach is more efficient and more
accurate.
Index Terms—Fractional Bratu-type equations; generalized
hat functions; operational matrix; error analysis; uniqueness;
numerical solution.
I. INTRODUCTION
RCTIONAL calculus is a 300 years old mathematical
discipline, and has been developed progressively up to
now. Compared with integer order differential equations,
fractional differential equations have the advantage that they
can better explain some natural physics processes and
dynamic system processes [1-5] because the fractional order
differential operators are non-local operators. Differential
equations involving fractional order derivatives are used to
describe a lot of systems, of which the important applications
lie in field of electrode-electrolyte polarization, heat
conduction, viscoelasticity, electromagnetic waves, diffusion
equations and so on [6-7]. In general, it is difficult to derive
the analytical solutions to most of the fractional differential
equations. Therefore, it is important to develop some reliable
and efficient techniques to solve fractional differential
equations. The numerical solutions of fractional differential
equations have attracted considerable attention from many
researchers. In recent years, an increasing number of
numerical methods are being developed. The most
commonly used methods are Variational Iteration Method
[8], Adomian Decomposition Method [9-10], Generalized
Manuscript received July 22, 2016; revised December 20, 2016.
Mulin Li is with the Inner Mongolia Vocational and Technical College of
Communications, Department of electronic and information engineering,
Inner Mongolia, Chifeng, China.
Lifeng Wang (Corresponding author) is with the School of Aeronautic
Science and Engineering, Beihang University, Beijing, China (e-mail:
Yu Liu is with the Inner Mongolia Vocational and Technical College of
Communications, Department of electronic and information engineering,
Inner Mongolia, Chifeng, China.
Differential Transform Method [11-12], and Wavelet
Method [13-14].
Bratu’s problem is also discussed in all kinds of
applications, such as chemical reaction theory, the fuel
ignition model of the thermal combustion theory and
nanotechnology [15-17]. About Bratu’s problem, both
mathematicians and physicists have devoted a lot of effort. In
Ref. [18], Syam and Hamdan presented the Laplace Adomian
decomposition method for solving Bratu’s problem. Wazwaz
[19] proposed the Adomian decomposition method for
solving Bratu’s problem. Yigit Aksoy and Mehmt Pakdemirli
[20] had solved Bratu-type equation of new perturbation
iteration solutions. Yi et. al [21] used CAS wavelets method
to solve fractional integro-differential equations of
Bratu-type.
The main objective of the present paper is to introduce
generalized hat functions operational matrix to solve the
fractional integro-differential equations of Bratu-type. In this
study, we consider the following equation:
( )
0( ) ( , ) ( ) 0
1 , 0 , 1
xu tD u x k x t e dt g x
r r x t
(1)
with initial condition: ( ) (0)j
ju b , 0,1, , 1j n (2)
Dis the fractional derivative in the Caputo sense, r is a
positive integer. is a real constant. ( )u x is the solution to
be determined. 2 2[0,1), ([0,1) [0,1))g L k L are
given functions.
The structure of this paper is as follows: In Section 2, the
generalized hat functions are introduced. The generalized hat
functions operational matrix of fractional integration is also
introduced and the error analysis of generalized hat functions
is given in Section 3. In Section 4, we summarize the
application of generalized hat functions operational matrix
method to the solution of the fractional integro-differential
equations of Bratu-type. In Section 5, uniqueness theorem of
this equation is proposed. Two numerical examples are
provided to clarify the method in Section 6. The conclusion is
given in Section 7.
II. GENERALIZED HAT FUNCTIONS AND THEIR PROPERTIES
The interval [0, ]T is divided into n subintervals
[ ,( 1) ]ih i h , 0,1,2, , 1i n , of equal lengths
h where /h T n . The generalized hat functions’ family of
Generalized Hat Functions Method for Solving
Fractional Integro-Differential Equations of
Bratu-type
Mulin Li1, Lifeng Wang2, Yu Liu1
F
IAENG International Journal of Computer Science, 44:1, IJCS_44_1_12
(Advance online publication: 22 February 2017)
______________________________________________________________________________________
first 1n hat functions is defined as follows [22]:
0
, 0 ,( )
0, ,
h xx h
x h
otherwise
(3)
( 1), ( 1) ,
( 1)( ) , ( 1) ,
0, ,
1,2, , 1,
i
x i hi h x ih
h
i h xx ih x i h
h
otherwise
i n
(4)
( ), ,
( )
0, .n
x T hT h x T
x h
otherwise
(5)
Using the definition of generalized hat functions, we have
following observations
1, ,( )
0,i
i kkh
i k
(6)
and
( ) ( ) 0, 2i jx x i j (7)
Any arbitrary function 2[0, ]u L T is approximated in
vector form as
1 1
0
( ) ( ) ( )n
T
i i n n
i
u x u x U x
(8)
where 1 0 1[ , , , ]T
n nU u u u and
1 0 1( ) [ ( ), ( ), , ( )]T
n nx x x x .
The important aspect of using the generalized hat functions
in the approximation of function ( )u x , lies in the fact that
the coefficients iu in Eq.(8) are given by
( ), 0,1,2, ,iu u ih i n (9)
III. OPERATIONAL MATRIX OF THE INTEGRATION FOR
GENERALIZED HAT FUNCTIONS
A. Fractional calculus
Before we derive the generalized hat functions operational
matrix of the fractional integration, we first review some
basic definitions of fractional calculus, which have been
given in [2].
Definition 1. The Riemann-Liouville fractional integral
operator J of order is given by
1
0
1( ) ( ) ( ) , 0
( )
x
J u x x u d
(10)
0 ( ) ( )J u x u x (11)
Definition 2. The Caputo definition of fractional differential
operator is given by
( )
10
( ), ;
1 ( )( ) ,
( ) ( )
0 1 .
r
r
rx
r
d u xr N
dx
uD u x d
r x
r r
(12)
The Caputo fractional derivatives of order is also defined
as ( ) ( )r rD u x J D u x , where rD is the usual integer
differential operator of order r . The relation between the
Riemann- Liouville operator and Caputo operator is given by
the following expressions:
( ) ( )D J u x u x (13)
1( )
0
( ) ( ) (0 ) , 0!
krk
k
xJ D u x u x u x
k
(14)
B. Fractional order generalized hat functions operational
matrix of integration.
In this part, we may simply introduce the operational
matrix of fractional integration of generalized hat functions,
more detailed introduction can be found in the Ref. [23].
If J is fractional integration operator of generalized hat
functions, we can get:
1 1 1( ) ( )n n nJ x P x
(15)
where
1 2 3
1 2 1
1 2
1
3
( 1) ( 1)
0
0 1
0 0 1
0 0 0 1( 2)
0 0 0 0 1
n
n
n
n
n
n n
hP
(16)
where 1( 1) ( 1) , 1,2, ,k k k k k n (17)
and 1 1 1( 1) 2 ( 1)
1,2, , 1
k k k k
k n
(18)
1nP
is called the generalized hat functions operational matrix
of fractional integration.
Apart from the generalized hat functions, we consider
another basis set of block pulse functions. The set of these
functions, over the interval [0, )T , is defined as:
1, ( 1)( )
0, ,i
ih x i hb x
otherwise
0,1,2, , 1i n (19)
with a positive integer value for n and T
hn
.
The following properties of block pulse functions will be
used in this paper
0,( ) ( )
( ),i j
i
i jb x b x
b x i j
(20)
IAENG International Journal of Computer Science, 44:1, IJCS_44_1_12
(Advance online publication: 22 February 2017)
______________________________________________________________________________________
0
0,
( ) ( ),
T
i j
i j
b x b x dx Ti j
n
(21)
Let 0 1 1( ) [ ( ), ( ), , ( )]T
n nB t b t b t b t . We suppose
( ) ( )n n nJ B x F B x , then nF is called the block
pulse operational matrix of fractional integration , here
1 2 1
1 2
3
1
0 11
0 0 1( 2)
0 0 0 1
n
n
n nF h
and
1 1 1( 1) 2 ( 1)k k k k ,
1,2, , 1k n .
There is a relation between the block pulse functions and
generalized hat functions, namely
1( ) ( )n nt B t (22)
where 1 0 1( ) [ ( ), ( ), , ( )]T
n nx x x x , and
( 1)
1/ 2 0 0 0
1/ 2 1/ 2 0 0
0 1/ 2 1/ 2 0
0 0 1/ 2 1/ 2
0 0 1/ 2n n
.
C. Error analysis
In this section, from Eq.(8), we suppose
0
( ) ( ) ( )n
n i
i
u x u ih x
(23)
and
1
0
1( ) ( ) ( )
( )
x
n nJ u x x u d
(24)
where ( )nJ u xdenotes the n th approximate of order
Riemann-Liouville fractional integral of ( )u x .
Let ( ) ( ) ( )n nx J u x J u x , then we have the
following theorem.
Theorem 3.1. If ( ), [0, ]u x x T is approximated by the
Eq.(8), then
(i) ( ) ( ) 0nu jh u jh , for 0,1,2, ,j n ;
(ii)2 3
1 1( ) ( ) ( )
2nu x u x u jh O
n n
,
for ( 1) , 0,1,2, , 1jh t j h j n ;
(iii) For ( 1)jh t j h ,
2
2 3
1( )
2 ( 1)n
MTx O
n n
,
where ( )u jh M , 0M .
Proof. (i) From Eq.(6), the value of ( )nu x at j th point
, 0,1,2, ,x jh j n is given by
0
( ) ( ) ( ) ( )n
n i
i
u jh u ih jh u jh
, then
( ) ( ) 0nu jh u jh , for 0,1,2, ,j n .
(ii) If ( 1) , 0,1,2, , 1jh t j h j n , then from
Eq.(3)-(5) and Eq.(23), we have
0
1
( ) ( ) ( )
( ) ( ) (( 1) ) ( )
( 1)( ) ( )
( ) ( ) ( ) ( )( )
( ) ( )( ) ( )
n
n i
i
j j
u x u ih x
u jh x u j h x
j h x x jhu jh u jh h
h h
u jh h u jh u jh h u jhu jh jh x
h h
u jh h u jhu jh x jh
h
(25)
when 0h , we obtain
( ) ( ) ( ) ( )nu x u jh x jh u jh (26)
Using the Taylor’s series of ( )u x , in the powers of
( )x jh , we have
( )
0
( )( ) ( )
!
kk
k
x jhu x u jh
k
(27)
where ( )ku denotes the k th order derivative of ( )u x . From
Eq.(26) and Eq.(27), we get
( )
2
23
( )( ) ( ) ( )
!
( )( ) ( )
2
kk
n
k
x jhu x u x u jh
k
x jhu jh O x jh
(28)
Because ( ) ,x jh h nh T , so we have
2
2 3
1( ) ( ) ( )
2n
Tu x u x u jh O
n n
(29)
(iii) According to the definition of the absolute error ( )n x ,
we obtain
1
0
( ) ( ) ( )
1( ) ( ) ( )
( )
n n
x
n
x J u x J u x
x u u d
(30)
For ( 1)jh t j h , we get
1
0
1( 1)
1
0
1
1( ) ( ) ( ) ( )
( )
( ) ( ) ( )1
( )( ) ( ) ( )
x
n n
jr h
nrh
r
x
njh
x x u u d
x u u d
x u u d
(31)
Substituting Eq.(29) into Eq.(31), we have
IAENG International Journal of Computer Science, 44:1, IJCS_44_1_12
(Advance online publication: 22 February 2017)
______________________________________________________________________________________
21( 1)
1
2 30
21
2 3
1 1( ) ( ) ( )
( ) 2
1( ) ( )
2
jr h
nrh
r
x
jh
Tx x u rh O d
n n
Tx u rh O d
n n
(32)
If ( )Max u kh M , 0,1,2, ,k j , then we obtain
1( 1)
12
02 3
1
2
2 3
2
2 3
( )1 1
( )( ) 2
( )
1
( 1) 2
1
2 ( 1)
jr h
rhr
nx
jh
x dMT
x On n
x d
x MTO
n n
MTO
n n
(33)
This completes the proof.
The fractional order integration of the function t was
selected to verify the correctness of matrix 1nP
. The
fractional order integration of the function ( )u t t is easily
obtained as follows
1(2)( )
( 2)J u x x
(34)
When 0.5, 32m , the comparison results for the
fractional integration is shown in Fig. 1.
Fig.1 0.5-order integration of the function ( )u x x .
IV. NUMERICAL SOLUTION OF EQ.(1)-(2)
In this section, the generalized hat functions method is
used for solving the fractional order integro-differential
equation of Bratu-type in the form Eq.(1). For this aim, we
approximate functions * ( )D u x, ( )g x and ( , )k x t in the
matrix forms.
Let 1 1( ) ( )T
n nD u x U x
, 1 1( ) ( )T
n ng x G x ,
1 1( , ) ( ) ( )T
n nk x t x K t . In this paper, we suppose
( )
0
( )
!
il
u t
i
u te
i
, then
1( )
1 1 1
0
1 1 1 1
( ) ( ) (0)!
( )
knT k
n n n
k
T T
n n n n
xu x U P x u
k
U P Q x
(35)
where coefficient 1nQ
is known and can be obtained by
using the initial conditions.
Substituting Eq.(22) into Eq.(35), we obtain
1 1 1 1
1 1 1
( ) ( )
( )
T T
n n n n
T T
n n n n
u x U P Q x
U P Q B x
(36)
Define 1 1 1 1 2[ , , , ]T T
n n n nU P Q a a a A
, then
( ) ( )nu x AB x .
Applying the properties of block pulse functions, we have
1 2[ ( )] [ , , , ] ( ) ( )i i i i
n n i nu x a a a B x A B x (37)
By substituting the above expanded forms into Eq.(1), we get
( )
0
1 1 1 10
0
1 1
1 1 10
0
1 1
1 1 1
0
( ) ( , ) ( )
[ ( )]( ) ( ) ( )
!
( )
( )( ) ( ) ( )
!
( )
1( ) ( ) ( ) (
!
xu t
jlxT T
n n n n
j
T
n n
T Tlx n jT T
n n n n
j
T
n n
lT T
n n n j n
j
D u x k x t e dt g x
u tU x x K t dt
j
G x
B t AU x x K B t dt
j
G x
U x x K diag A Bj
0
1 1
1
1 1 1
0
1 1
1
1
0
1
1 1
)
( )
1( ) ( ) ( ) ( )
!
( )
1( ) ( ) ( ) ( )
!
( )
( ) ( ) ( ) 0
x
T
n n
lT T
n n n j n n
j
T
n n
lT T T
n n n j n n
j
T
n n
T T T
n n n n n n
t dt
G x
U x x K diag A F B xj
G x
U B x B x K diag A F B xj
G B x
U B x W B x G B x
(38)
where nW is a n -vector with elements equal to the diagonal
entries of the following matrix
1
0
1( )
!
lT
j n
j
W K diag A Fj
(39)
Putting the collocation points 1
0
n
i ix
into Eq. (38), Eq.(38)
will be
1 1 0T T T
n n nU Q G (40)
Solving the system of equations given by Eq.(40), the
numerical solution ( )u x is obtained. The Eq.(40) can be
solved by iterative numerical technique such as Newton’s
method. Also the Matlab function “fsolve” is available to
deal with such a nonlinear system of algebraic equations.
IAENG International Journal of Computer Science, 44:1, IJCS_44_1_12
(Advance online publication: 22 February 2017)
______________________________________________________________________________________
V. EXISTENCE OF UNIQUENESS
Theorem1. (Uniqueness theorem) Eq. (1) has a unique
solution whenever 0 1 , where =( ) ( 1)
ML
,
0 , 1
sup ( , )x t
M k x t
。
Proof. Suppose 0,1t , then ( )u x is bounded. Therefore
the nonlinear term ( )u te in Eq. (1) is Lipschitz continuous
with *
*
uue e L u u , 0L .
Letu and*u be two different solutions of Eq. (1) , then we
can get
( )
0( ) ( , ) ( )
xu tD u x k x t e dt g x (41)
* ( )
*0
( ) ( , ) ( )x
u tD u x k x t e dt g x (42)
Using Rieman-Liouville fractional integration, we have
1
0
1 ( )
0 0
1( ) ( ) ( )
( )
( ) ( , )( )
x
xu t
J D u x x g d
x k t e dtd
(43)
*
1
*0
( )1
0 0
1( ) ( ) ( )
( )
( ) ( , )( )
x
xu t
J D u x x g d
x k t e dtd
(44)
Because
1( )
0
( ) ( ) (0 )!
knk
k
tJ D x t x t x
k
, so Eq. (43)
and Eq. (44) can be transformed into 1
( ) 1
00
1 ( )
0 0
1( ) (0) ( ) ( )
! ( )
( ) ( , )( )
jn xj
j
xu t
xu x u x g d
j
x k t e dtd
(45)
*
1( ) 1
* *0
0
( )1
0 0
1( ) (0) ( ) ( )
! ( )
( ) ( , )( )
jn xj
j
xu t
xu x u x g d
j
x k t e dtd
(46)
Then we have
*
*
*
1 ( )
0 0
*
( )1
0 0
( )1 ( )
0 0
( )1 ( )
0 0
1
*0
( ) ( , )( )
( ) ( , )( )
( ) ( , )( )
( ) ( , )( )
( )( )
( )
xu t
xu t
xu tu t
xu tu t
x
x k t e dtd
u u
x k t e dtd
x k t e e dtd
x k t e e dtd
MLu u x d
MLu
1 1
*
*
1
( ) ( 1)
x xu
MLu u
Therefore * 1 0( ) ( 1)
MLu u
.
This implies that* (1 ) 0u u , where
=( ) ( 1)
ML
.
As 0 1 ,* 0u u , imply
*u u , so we can prove
Eq.(1) has the uniqueness solution.
VI. NUMERICAL EXAMPLES
To test the efficiency and accuracy of the proposed
generalized hat functions operational matrix of fractional
integration method, here we consider two examples and
suppose l n .
Example 6.1. Consider the following equation [21]:
0.5 ( )
0
1( ) ( ) ( ) 0
2
xu tD u x x t e dt g x (47)
where
21.5 0.5(3) (2)( ) ( 1)
(2.5) (1.5) 2
x xxg x x x e
, and
subject to the initial condition (0) 0u . The exact solution
of this problem is 2( )u x x x . Table I shows the
absolute errors obtained by generalized hat functions and
CAS wavelets (see [21]) method, respectively. The
comparison between the numerical solutions and the exact
solution by generalized hat functions and CAS wavelets
method are shown in Fig.2-4.
IAENG International Journal of Computer Science, 44:1, IJCS_44_1_12
(Advance online publication: 22 February 2017)
______________________________________________________________________________________
TABLE I.
ABSOLUTE ERRORS AT DIFFERENT POINTS FOR DIFFERENT n .
t 6n 12n 24n
Ours CAS Ours CAS Ours CAS
0 0 0.05345 0 0.02590 0 0.00591
1/6 0.02885 0.06527 0.00899 0.03850 0.00303 0.00861
2/6 0.01991 0.05142 0.00658 0.01273 0.00222 0.00925
3/6 0.01690 0.02376 0.00556 0.00782 0.00186 0.00174
4/6 0.01518 0.03786 0.00496 0.00811 0.00165 0.00314
5/6 0.01404 0.08725 0.00456 0.04440 0.00150 0.03718
Fig.2. The comparison between numerical and exact solution for 6n .
Taking a closer to Table I and Fig. 2-4, with k increasing,
we see that the approximate solutions converge to the exact
solution. From the comparison between two methods, we
find that generalized hat functions method can reach higher
degree of accuracy when solving the same equation.
Fig.3. The comparison between numerical and exact solution for 12n .
Fig.4. The comparison between numerical and exact solution for 24n .
Example 6.2. Consider this equation:
( )
0( ) 3 ( ) ( ) 0,
xu tD u x x t e dt g x (48)
such that the initial conditions (0) 0u ,
and2( ) 1/ 1 3 ( 1)/2g x x x x . The value of
1 is the only case for which we know the exact solution
( ) ln( 1)u x x . The numerical results are calculated
when the parameter 24n . The numerical solutions for
various are presented in Fig.5.
Fig.5. Numerical solution and exact solution of 1 .
The numerical results in Fig.5 corresponding to 1 are
in good agreement with the exact results. Therefore, we hold
that the solutions for 0.75 and 0.85 are also
credible.
VII. CONCLUSION
In this work, we introduce the generalized hat functions
and operational matrix of the fractional integration. Using
this matrix and block pulse functions to solve the fractional
integro- differential equations of Bratu-type numerically.
The error analysis of generalized hat functions and the
uniqueness theorem of this equation are proposed. The
present method is better than CAS wavelets method.
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IAENG International Journal of Computer Science, 44:1, IJCS_44_1_12
(Advance online publication: 22 February 2017)
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