In this paper, we study semi-analytical methods entitled fuzzy fractional differential transform method to solve fuzzy impulsive fractional differential equations using Caupto fractional derivative. At the end first of all fuzzy differential transform method in fractional case is defined and its properties are considered completely. Then existence and uniquness theorem for the solution are proved and convergence of the proposed method is considered in details. Some examples indicate that this method can be easily applied to many linear and nonlinear problems.
Fuzzy set theory is the significant tool for modeling unknown problems and can be found in many branches of regional, physical, mathematical and engineering sciences. As a result many things can happen in the real world has a fuzzy meaning. The concept of the fuzzy set theory was first proposed by Zadeh, S. Chang, Zimmerman and Kaleva (see [13, 17, 36]). One of the very important branches of the fuzzy theory is fuzzy differential equations. Then Kandel and Byatt [18] have contributed greatly to the development of fuzzy differential equations. Later many scientists, including M. Friedman et al. [15] applied numerical methods to solve this equations. Also the idea of fuzzy differential equations has been studied by scientists and engineers such as T. Allaviranloo et al. [2, 3] and Dong Qiu et al. [23, 24]. They have considered new method to solve fuzzy differential equation based on fuzzy Taylor expansion as one of the branches of fuzzy differential equations. The idea of the theory of fuzzy impulsive differential equation has been emerging as an effective tool area of investigation in recent years (see [25]). Mouffak Benchohra et al. [11] proposed fuzzy solutions for impulsive differential equations. Subsequently, the basic result for fuzzy impulsive differential equation was defined by S. Vengataasalam et al. [30].
Although the fuzzy fractional differential equations have many branches and many applications and in this research we will restrict our attention to fuzzy impulsive fractional differential equations while fuzzy impulsive fractional differential equations are usually hard to solve analytically and the exact solution is rather difficult to be obtained. There are not too many papers on fuzzy impulsive fractional differential equation up to now. Our aim in this paper is to study the semi-analytical methods for solving fuzzy impulsive fractional differential equations. We will use the fuzzy fractional differential transform method (FFDTM) based on generalized Hukuhara differentiability to solve a nonlinear and linear fuzzy impulsive fractional differential equations given by
In this paper the set of all fuzzy real numbers is denoted RF. It is clear that R ⊂ RF. Where , denote the Caputo fractional generalized derivative of order , and f : J × RF → RF, is continuous fuzzy function, Ik : R → R, is continuous function, represent the right and left limits of y (t) at t = tk. This paper shows that some difficult fuzzy impulsive fractional differential equations can be easily calculated by fuzzy fractional differential transform method.
The paper is organized as follows: We describe the basic notation and prelimition in Section 2. We define the fuzzy fractional differential transform method expansion such that f is generalized Hukuhara differentiable in Section 3. In Section 4, we shall provide extremely useful basic properties of generalized fuzzy fractional differential transform. We describe the fuzzy fractional impulsive differential equation in Section 5. Some numerical examples are given to clarify the details and efficiency of the method in Section 6. This paper ends with conclusion in Section 7.
Preliminaries
In this section, we introduce Definitions, Propositions, Lemmas, Theorems and provided the new Theorem will be needed throughout the paper.
We denote CF [a, b] as the space of all continuous fuzzy-valued function on [a, b]. Also, we denote the space of all Lebesgue integrable fuzzy-valued function on the bounded interval [a, b] ⊂ R by LF [a, b].
Definition 2.1. [7] Let f (x) ∈ CF [a, b] ∩ LF [a, b], and , and such that for all 0 ≤ r ≤ 1, then the Caputo definition of fractional differential operator is given by
where
and
is the Caputo fractional derivative of order .
Definition 2.2. Let f : [a, b] → RF and x0 ∈ (a, b), with and both differentiable at x0 for all r ∈ [0, 1]. We say that f is [(i) - gH]-differentiable at x0 if
-f is [(ii) - gH]-differentiable at x0 if
Definition 2.3. [10] We say that a point t0 ∈ (a, b), is a switching point for the differentiability of f, if in any neighborhood v of t0 there exist points t1 < t0 < t2 such that
type(I): at t1 (2.4) holds while (2.5) does not hold and at t2 (2.5) holds while (2.4) does not hold, or
type(II): at t1 (2.5) holds while (2.4) does not hold and at t2 (2.4) holds while (2.5) does not hold.
Here, we introduced the fuzzy fractional Taylor formula under the Caputo-type derivatives as follow:
Definition 2.4. Let f (x) ∈ CF [a, b] ∩ LF [a, b]. And suppose that
where Then we have
Lemma 2.[5] Let fgH ∈ Cf (R, RF), n ∈ N. Then the following integrals
are continuous functions in xn-1, xn-2, …, x respectively. Here xn-1, xn-2, …, x > x0 and all are real numbers. is the Caputo fractional derivative of order , and
Lemma 3.Consider fgH : [a, b] → RF is gH-differentiable and continuous on [a, b]. Then
Proof. The proof is obvious using the definition.
Theorem 2.1.Let and f (x) ∈ CF [a, b] ∩ LF [a, b]. Consider fgH (t) : [a, b] → RF is gH-differentiable such that type of differentiability fgH (t) in [a, b] does not change. Then for a < t < b and
If fgH (t) is [(i) - gH]-differentiable then is fuzzy Riemann-integralable over [a, b] and
For case [(ii)-gH]-differentialablity we have
Proof 3. The proof is clear.
Fuzzy fractional differential transform method
In this section, we are going to introduce the fuzzy fractional differential transform method. The proposed method is based on generalized Taylor’s formula. We define the generalized fractional differential transform of the k-th derivative of function f (x) in one varible as follows:
where k-times and the differential inverse transform of is defined as follow:
if we substitute Equation (3.1) into Equation (3.2), using the generalized Taylor’s formula, then we get
Where is he order of fractional and F (k) is the fractional differential transform of f (x). We define the fuzzy fractional differential transform for any positive integer k and any , then the follwing equality holds, which is
if f (x) is [(i)-gH]-differentiability then:
And
if f (x) is [(ii)-gH]-differentiability then:
Fuzzy fractional differential transform theorem
In section, we are going to prove fuzzy fractional differential transform expansion for fuzzy valued function in four different cases by using concept of generalized Hukuhara differentiability.
Theorem 3.1.Let with and For x ∈ T
If are [(i)-gH]-differentiability has no change. Then
where
and
where ,for each x ∈ (a, b] and is the Caputo fractional derivative of order , and
If are [(ii)-gH]-differentiability has no change. Then
If are [(i)-gH]-differentiable for i = 2k - 1, k ∈ N, and are [(ii) - gH]-differentiable for i = 2k, k ∈ N ∪ {0}
where
and
If are [(i)-gH]-differentiable for i = 2k, k ∈ N, and are [(ii) - gH]-differentiable for i = 2k - 1, k ∈ N ∪ {0}
where
and
Suppose that Furthermore let f in [a, ξ] is [(i) - gH]-differentiable and in [ξ, b] is [(ii) - gH]- differentiable, in fact ξ is switching point type I for first order derivative of f and t0 ∈ [a, ξ] in neighborhood of ξ. Moreover suppose that second order derivative of f in ζ1 ∈ [t0, ξ] has switching point type II. Moreover type of differentiability for on [ξ, b], does not change. So
Proof 4. We prove only the case (iv) and the proof of other cases are similar to this case.
(iv) According to the hypothesis f is [(i) - gH]-differentiable in [x0, ξ], by Theorem 2.1
and f is [(ii) - gH]-differentiable in [ξ, b], so for x ∈ [ξ, b]
The point ξ is a switching point for differentiability so from Equations (3.16) and (3.17) we obtain
Consider the first integral on the right of the above equation. By hypothesis ζ is switching point type II for gH-derivative of the function f. So is [(ii) - gH]-differentiable on [x0, ζ1], then type of differentiability change. Using Theorem 2.1 we deduce that
Since is [(i) - gH]-differentiable on [ζ1, ξ], such that the type of differentiability does not change. Hence, for x1 ∈ [ζ1, ξ], we have
So, the first integral on the rigth hand side of Equation (3.18) is as follow
Consider the second integral on the rigth side of the Equation (3.18). According to the hypothesis f(i), i = 2, 3 are [(ii) - gH]-differentiable on [ξ, b]. We have
In this section we prove all theorems about generalized fuzzy fractional differential transform by using Theorem 3.1. If are the differential transforms of functions f (x), g (x), h (x) andw (x) respectively, the following theorems are established.
Theorem 4.1.If f (x) = g (x) ± h (x), then .
Theorem 4.2.If f (x) = ag (x), then
Proof 5. The proof is similar to proof Theorem 4.1.
Theorem 4.3.If f (x) = g (x) h (x), then
Proof 6. (i). If are [(i)-gH]-differentiability has no change. Then
(ii). If are [(ii)-gH]-differentiability has no change. Then
(iii). If are [(i)-gH]-differentiable for i = 2k - 1, k ∈ N, and fi are [(ii) - gH]-differentiable for i = 2k, k ∈ N ∪ {0}
Theorem 4.4.If f (x) = g1 (x) g2 (x) g3 (x) … gn-1 (x) gn (x) then
Proof 7. The proof is based on the same way as Theorem 4.3.
Theorem 4.5.If , then
Proof 8. (i). If are [(i)-gH]-differentiability has no change. Then
(ii). If are [(ii)-gH]-differentiability has no change. Then
(iii). If are [(i)-gH]-differentiable for i = 2k - 1, k ∈ N, and fi are [(ii) - gH]-differentiable for i = 2k, k ∈ N ∪ {0}
Theorem 4.6. If , then
Proof 9. The proof is based on the same way as Theorem 4.5.
Theorem 4.7.If then
Proof 10. (i). If are [(i)-gH]-differentiability has no change. Then
By using Theorems 4.3 and 4.6, we get
(ii). If are [(ii)-gH]-differentiability has no change. Then
By using Theorems 4.3 and 4.6, we get
(iii). If are [(i)-gH]-differentiable for i = 2k - 1, k ∈ N, and fi are [(ii) - gH]-differentiable for i = 2k, k ∈ N ∪ {0}
By using Theorems 4.3 and 4.6, we get
Theorem 4.8.If f (x) = (x - x0) p, then where
Proof. The proof is left to the reader.
Theorem 4.9., then by choosing a suitable β ∈ z+ such that we have
Proof 12. The proof is based on the same way as Theorem 4.6.
Fuzzy impulsive fractional differential equation
Consider the following fuzzy impulsive fractional differential equation
where is a real number and the operator denote the Caputo fractional generalized derivative of order , and f : J × RF → RF, is continuous fuzzy function. Also I : R → R is continuous function. In this section, using fractional differential transform method for fuzzy impulsive fractional differential Equation eqrefk : 1 under the conditions eqrefe : 2 and eqrefe : 3 with fuzzy initial conditions is solved under cf [gH]-differentiability.
Lemma 4.[8, 16] The initial value problem eqrefk : 1 under the conditions eqrefe : 2 and eqrefe : 3 is equivalent to one of the following integral equations:
if y (t) be cf [(i) - gH]-differentiable,
if y (t) be cf [(ii) - gH]-differentiable,
if there exists a point t1 ∈ (0, tk+1) such that y (t) is [(i) - gH]-differentiable on [0, t1] and [(ii) - gH]-differentiable on (t1, tk+1).
Theorem 5.1.Assume that
There exists a constant 0 ≤ l such that
There exists a constant 0 ≤ l* such that
if
Such that T is very small numbers therefore, Equations (5.1)–(5.3) has a unique solution on [0, T].
Proof 13. We transform the problems (5.1)–(5.3) into a fixed point problem. Now we introduce
and there exist and with , that is a closed and convex subset of the Banach space of all continuous function on (0, k + 1]. Therefore, pc is a Banach space, too. We suppose that the solution of problems (5.1)–(5.3) is in case [i - gH]-differentiability and [ii - gH]-differentiability is equivalent to integral Equation (5.6). So, we define a mapping
that given by
Therefore, the fixed point of the operator F is the solution of the problems (5.1)–(5.3). We shall use the Banach contraction principle to prove that F has a fixed point. We will show that F is a contraction map. Let x, y ∈ pc (J, RF). Then, for each t ∈ [0, T], and using the Lemma 1 we have
Therefore,
Consequently by (5.9), F is a contraetion. As a consequence of Banach fixed point theorem, we deduce that F has a fixed point which is a solution of problems (5.1)–(5.3).
Let us define . Suppose that Y (K), W (K) andF (K) are the fractional differential transform of the function y (t), w (t) and f (t, y (t)), respectively. Then, by choosing β ∈ z+ such that and using the Theorem 4.9, we obtain
with
Therefore, the solution of (5.1)–(5.3) falls short of providing an explicit farmula
for k = 0, 1, 2, …, (nα - 1), where is the order of the fuzzy impulsive fractional differential equation.
Theorem 5.2.Let then the exact solution of Equations (5.1)–(5.3) could be represented by
Also, the approximate solution y (t) can be obtained by taking finitely many terms in the series representation of y (t) so,
is the exact solution of Equations (5.1)–(5.3). Also let us y (t) and yN (t) be exact and approximate solution of the problems (5.1)–(5.3). We will show that,
Also
Therefore if y (t) and yN (t) be exat and approximate solution of the problems (5.1)–(5.3), without loss of generality suppose that there exists a point t1 ∈ (0, tk+1) such that y (t) is [(i) - gH]-differentiable on [0, t1] and [(ii) - gH]-differentiable on (t1, tk+1). Using Lemma (4), the solution of problems (5.1)–(5.3) in this case is equivalent to integral Equation (5.6). By using Lemma 1 we have,
And
Thus
It follows that
Also
where M1, M2 are constants.
Hence ||d (y (t), yN (t)) ||0→ 0 asn → ∞, the approximate solution convergence uniformly to the exact solution y (t) and its fractional derivative, respectively. The proof for othere case is similar.
Now we claim that solving fuzzy impulsive fractional differential Equations (5.1)–(5.3) by fuzzy fractional differential transform method is convregece.
Theorem 5.3.Cansider the fuzzy impulsive fractional differential Equations (5.1)–(5.3) if there exists a fixed n such that n ≤ k, |f (t, y (t)) | ≤ rk, 0 < r ≤ 1 and then the numerical solution of the present method absolutely convergence.
Proof 15. Without loss of generality suppose the exists a point t1 ∈ (0, tk+1) such that y (t) is [(i) - gH]-differentiable on [0, t1] and [(ii) - gH]-differentiable on (t1, tk+1), proof of the other cases are left to the reader. For simplicity, let . We suppose that the solution of problems (5.1)–(5.3) is [(i) - gH]-differentiable on [0, t1] and [(ii) - gH]-differentiable on (t1, tk+1). Using Lemma (4), the solution of problem (5.1)–(5.3) is equivalent to integral Equation (5.6). So the fuzzy fractional differential transformation of (5.6) is
Suppose is true for all n ≤ k. From (5.25), we have
Let
And
k is large enough, we now proceed by induction, the hypothesis is true. So we have
Numerical examples
We demonstrate the effectiveness of the fuzzy fractional differential transform method,for solving fuzzy impulsive fractional differential equations by the following some examples.
Example 6.1. Let us consider the fuzzy impulsive fractional equation,
In this paper a new approach by presenting fuzzy fractional differential transform expansion based on gH-differentiability was introduced. The numerical results show that the present method is an accurate and reliable analytical technique for fuzzy impulsive fractional differential equation. Moreover, the method can be effective for solving other nonlinear initial value problems.
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