Theoretical Mathematics & Applications, vol.6, no.1, 2016, 1-14 ISSN: 1792-9687 (print), 1792-9709 (online) Scienpress Ltd, 2016 Numerical solutions of integro-differential equation with purely integral condition by using Laplace transform method Moussa Zakari Djibibe1 , Nadjime Pindra2 and Kokou Tcharie3 Abstract The aims of this paper are to prove the existence, uniqueness and continuous dependence upon the data of solution of following intogrodifferential hyperbolique equation with purely integral conditions. Z t ∂2u ∂2u ∂u + αu(x, t) = ϑ(t − s)u(x, s) ds, 0 < x < `, 0 < t ≤ T, −a 2 −c ∂t2 ∂x ∂x 0 u(x, 0) = φ(x), 0 < x < `, ∂u (x, 0) = χ(x), 0 < x < `, ∂t Z ` u(x, t) dx = E(t), 0 < t ≤ T, 0 Z ` xu(x, t) dx = G(t), 0 < t ≤ T. 0 The proofs are based on a priori estimates and Laplace transform method. We present a numerical approximate solution to integro-differential equation with integral conditions. A Laplace transform method is described 1 2 3 Département de Mathématiques, Université de Lomé, PO Box 1515 Lomé, Togo. E-mail: zakari.djibibe@gmail.com Département de Mathématiques, Université de Lomé, Togo. E-mail: nadjimepindra@gmail.com Département de Mathématiques, Université de Lomé, Togo. E-mail: tkokou09@yahoo.fr Article Info: Received : July 31, 2015. Revised : August 30, 2015. Published online : November 22, 2015. 2 Numerical solutions of integro-differential equation... for the solution of considered equation. Following Laplace transform of the original problem, an appropriate method of solving differential equations is used to solve the resultat time-independent modified equation and solution is inverted numerically back into the time domain. Numerical results are provided to show the accuracy of the proposed method. Mathematics Subject Classification: 35B45; 35L82; 44A10 Keywords: Laplace transform method; Integral conditions; Continuous dependence; Integro-differential 1 Introduction In this paper, we deal with a class of hyperbolic integro-differential equation with purely nonlocal conditions. The precise statement of the problem is a follows : let ` > 0, T > 0, and Ω = {(x, t) ∈ R2 : 0 < x < `, 0 < t < T }. We shall determine a solution u, in Ω of the differential equation ∂ 2u ∂ 2u ∂u −a −c +αu(x, t) = 2 2 ∂t ∂x ∂x Z t ϑ(t − s)u(x, s) ds, 0 < x < `, 0 0 < t ≤, T (1) satisfying the initial conditions u(x, 0) = φ(x), 0 < x < `, ∂u (x, 0) = χ(x), 0 < x < `, ∂t (2) (3) and the integral conditions Z ` u(x, t) dx = E(t), Z 0 < t ≤ T, (4) 0 ` xu(x, t) dx = G(t), 0 < t ≤ T, (5) 0 where ϑ, ξ, φ, E, G are known functions, `, T and a are pasitive constants, and α, c are the reals. M.Z. Djibibe, N. Pindra and K.Tcharie 3 Assumption 1.1. For all x, t) ∈ Ω, we assume that ϑ0 ≤ ϑ(x, t) ≤ ϑ1 , ϑ0 > 0, ϑ1 . > 0 φ is continuously derivate on (0, `). The notion of nonlocal condition has been introduced to extend the study of the classical initial value problems and it is more precise for describing nature phenomena than the classical condition since more information is taken into account, thereby decreasing the negative effects incurred by a possibly erroneous single measurement taken at the initial value. The inportance of nonlocal conditions in many applications is discussed in [10], [16]. Mathematical modelling by evolution problems with a nonlocal constraint of the form Z 1 1 u(x, t) dx = ζ(t) 1−` ` is encountered in heat transmission theory, thermoelasticity, chemical engineering, underground water flow, and plasma physic. Many methods were used to investigate the existence and uniqueness of the solution of mixed problems which combine classical and integral conditions. J. R. Cannon [5] used the potentiel method, combining a Dirichlet and an intégral condition for a parabolic equation. L.A. Mouravey and V. Philinovoski [9] used the maximum principle, combining a Neumann and an integral condition for heat equation. M.Z. Djibibe and K. Tcharie [13], Ionkin [6] and L. Bougoffa [4] used the Fourier method for same purpose. Recently, mixed problems with integral conditions for generalization of equation (1) have been treated using the energy-integral method. See M.Z. Djibibe and K. Tcharie [11] , M.Z. Djibibe and K. Tcharie [12], M.Z. Djibibe el al. [14], [15], N.I. Yurchuk [16], [17], M. Mesloub, A. Bouziani and N. Kechkar [8]. Differently to these works, in the present paper we combine a priori estimate and Fourier’s method to prove existence and uniqueness solution of the problem (1)- (5). The results obtained in this paper generalize the results of [1], and constitute a new contribution to this emerging field of research. It can be a part in the contribution of the development of a priori estimates an Laplace methods for solving such problems. The questions related to these problems are so miscellaneous that the elaboration of a general theory is still premature. Therefore, the investigationof these problems requires at every time a separate study. 4 Numerical solutions of integro-differential equation... The remainder of the paper is organized as follows. After this introduction, in section 2, we present some preliminaries and basic lemmas. Then in Section 3, we establish a priori estimate. Finally, in section 4, we prove existence solution. 2 Preliminaries We transform the problem (1)-(5) with nonhomogeneous boundary conditions (4) and (5) into a problem with homogeneous boundary conditions. For this, we introduce a new unknow function defined by u(x, y) = v(x, t)+w(x, t), where 2` − 4x 4x − 2` 4x − 2` w(x, t) = E(t) + G(t) = (G(t) − E(t)). 4 4 ` ` `4 Then, problem becomes : ∂2v ∂2v ∂v − a −c + αv(x, t) = f (x, t), 2 2 ∂t ∂x ∂x v(x, 0) = ϕ(x), 0 < x < `, ∂v (x, 0) = ψ(x), 0 < x < `, ∂t Z ` v(x, t) dx = 0, 0 < t ≤ T, 0 Z ` xv(x, t) dx = 0, 0 < t ≤ T, 0 < x < `, 0 < t ≤ T, (6) (7) (8) (9) (10) 0 where 4x − 2` (G(0) − E(0)), `4 4x − 2` 0 (G (0) − E 0 (0)), ψ(x) = χ(x) − `4 ϕ(x) = φ(x) − Z t f (x, t) = ϑ(t − s)u(x, s) ds − 0 2(2x − `) 00 (G (t) − E 00 (t)) 4 ` 2(2αx − α` − 2c (G(t) − E(t)). `4 Instead of searching for the function u, we search for the function v. So the solution of problem (1), (2), (3), (4) and (5) will be given by u(x, t) = v(x, t) + w(x, t). − 5 M.Z. Djibibe, N. Pindra and K.Tcharie Lemma 2.1 (Gronwall). Let x(t) ≥ 0, h(t), y(t) the integrables fonctions on [a; b]. If Z t y(t) ≤ h(t) + x(τ )y(τ ) dτ, ∀t ∈ [a; b] a then Z Z t y(t) ≤ h(t) + t h(τ )x(τ ) exp( a x(s) ds) dτ, ∀t ∈ [a ; b]. τ In particular, if x(t) ≡ c is invariable fonction and h(t) is an increasing fonction, then y(t) ≤ h(t)ec(t−a) , ∀t ∈ [a ; b]. 3 Main Results 3.1 Uniqueness and Continuous Dependence of the solution Theorem 3.1. If v(x, t) is a solution of problem (1), (2), (3), (4) and (5), then we have a priori estimates ¶ µZ ` Z `µ µ ¶ Z ` ∂u 2 2 2 2 sup Jx ϕ (x) dx + Jx2 ψ(x) dx + Jx u dx + u dx ≤A ∂t 0≤t≤T 0 0 0 ¶ Z ` + Jx2 ϕ(x) dx . (11) 0 ∂u Proof. Appying Jx to (1), Multiplying with Jx and integrating the re∂t sults obtained over Ωτ = (0, `) × (0, τ ). Observe that Z `Z τ µ 2 ¶ µ ¶ Z `Z τ µ 2 ¶ µ ¶ ∂ v ∂v ∂v ∂ v Jx Jx Jx dt dx − a Jx dt dx 2 2 ∂t ∂t ∂x ∂t 0 0 0 0 Z `Z µ τ −c Jx 0 0 ∂v ∂x ¶ µ ∂v Jx ∂t Z `Z τ = 0 0 ¶ ¶ ∂v dt dx + α Jx v(x, t)Jx dt dx ∂t 0 0 µZ t ¶ µ ¶ ∂v Jx ϑ(t − s)u(x, s) ds Jx dt dx, (12) ∂t 0 Z `Z τ µ 6 Numerical solutions of integro-differential equation... Z x where Jx (u(x, t) = u(ξ, t) dξ. Successive intrgration by parts of integrals 0 on the left-hand of (12) are straight-foward but somewhat tedious. We give only their results µ ¶ Z Z Z Z 1 ` 2 1 ` 2 ∂u(x, τ ) α ` 2 α ` 2 dx − J J ψ(x) dx + J u dx − J ϕ(x) dx 2 0 x ∂t 2 0 x 2 0 x 2 0 x Z Z Z a ` 2 a ` 2 ∂u + u dx − ϕ (x) dx = a u(`, t) dxdt 2 0 2 ∂t Ωτ µ ¶ 0 ¶ µ ¶ Z µ Z ∂u ∂u ∂u dxdt − a (0, t) + u(0, t) Jx dxdt +c uJx ∂t ∂x ∂t Ωτ Ωτ ¶ µ ¶ Z ` Z τ µZ t ∂v + Jx ϑ(t − s)u(x, s) ds Jx dt dx. (13) ∂t 0 0 0 By the Cauchy inequality, ¶ µ ¶ Z Z ` Z τ µZ t ∂v T ϑ0 Jx2 u dx dt Jx ϑ(t − s)u(x, s) ds Jx dt dx ≤ ∂t 2 ΩT 0 0 0 Z TZ ` µ ¶ ∂u ϑ0 T + Jx2 dx dτ, (14) 2 0 0 ∂t µ ¶ Z Z Z ∂u 1 1 ∂u 2 2 u dxdt + Jx dxdt, (15) u(`, t) dxdt ≤ ∂t 2 ΩT 2 ΩT ∂t Ωτ µ ¶ µ ¶ Z Z Z ∂u ∂u 1 1 2 2 uJx u dxdt + Jx dxdt ≤ dxdt. (16) ∂t 2 ΩT 2 ΩT ∂t Ωτ Substuting (16) into (15), yields µ ¶ Z Z Z Z 1 ` 2 ∂u(x, τ ) α ` 2 a ` 2 a ` 2 J dx + J u dx + u dx ≤ ϕ (x) dx 2 0 x ∂t 2 0 x 2 0 2 0 Z Z Z 1 ` 2 α ` 2 |a| + T ϑ0 + |c| + Jx ψ(x) dxAutof orm + Jx ϕ(x) dx + u2 dxdt 2 0 2 0 2 ΩT µ ¶ Z Z ϑ0 T + |c| + 1 ∂u T ϑ0 + Jx2 Jx2 u dxdt. (17) dx dτ + 2 ∂t 2 ΩT ΩT The right-hand side of (17) is independent of τ, hence, replacing the left-hand side by the upper bound with respect to τ and by Gronwall Lemma, we get ¶ ¶ µZ ` Z `µ µ ∂u(x, τ ) 2 2 2 λT + Jx u dx + u dx ≤ e sup Jx ϕ2 (x) dx ∂t 0≤τ ≤T 0 0 ¶ Z ` Z ` + Jx2 ψ(x) dx + Jx2 ϕ(x) dx , (18) 0 0 7 M.Z. Djibibe, N. Pindra and K.Tcharie where µ max λ= ¶ 1 α T ϑ0 + |c| + 1 T ϑ0 + |a| + |c| , , , 2 2 2 2 µ ¶ . 1 α a min , , 2 2 2 From (18), we obtain the priori estimates (11). This complete the proof of Theoreme (3.1), with A = eλT . Corollary 3.2. If problem (1), (2), (3), (4) and (5) has a solution, then this solution is unique and depends continuously on (ϕ, ψ). 3.2 Existence of the Solution Laplace transform is widely used in the area of engineering technology and mathematical science. There are many problems whose solution may be found in terms of the Laplace. In fact, it is an efficient method for solving many diffential equations and partial differential equation. The mains difficult of the method of Laplace domain into the real domain. Hence in this section, we apply the technique of the Laplace transform to find solutions of the problem (1)-(5). Suppose that v(x, t) is défined and is of the exponential order for t ≥ 0, there exists λ > 0, β > 0 and t0 > 0 such that |v(x, t)| ≤ λeβt for t ≥ t0 . Then the Laplace transform V (x, s) includind the function v(x, t) is defined by Z +∞ V (x, s) = v(x, t)e−st dt, (19) 0 where s is know as a Laplace variable and V is a function in the Laplace domain. Applying the Laplace transform on both sides of (14), we obtain Z +∞ 0 ∂ 2 v −st e dt−a ∂t2 Z +∞ ∂ 2 v −st e dt − c ∂x2 Z +∞ ∂v −st e dt+ ∂x 0 0 Z +∞ Z +∞ Z t −st +α v(x, t)e dt = ϑ(t − s)v(x, s) ds dt. (20) 0 0 0 8 Numerical solutions of integro-differential equation... The standard integration by parts of the terms on the left-hand of (20), leads Z +∞ Z 0 Z 0 +∞ +∞ 0 ∂ 2 v −st e dt = −ψ(x) − sϕ(x) + s2 V (x, s), 2 ∂t d2 V (x, s) ∂ 2 v −st e dt = , ∂x2 dx2 ∂v −st dV (x, s) e dt = . ∂x dx (21) (22) (23) Substuting (21), (22) and (23) into (20), we get d2 V (x, s) dV (x, s) −c + (α + s2 )V (x, s) = f (x, s) + ψ(x) + sϕ(x), (24) 2 dx dx Z +∞ Z t where f (x, s) = ϑ(t − s)v(x, s) ds dt. −a 0 Similarly, we have 0 Z Z ` V (x, s) dx = 0, (25) xV (x, s) dx = 0. (26) 0 ` 0 Now, we distinguish the following cas : I Case 1 : If c2 + 4aα + 4as2 = 0. I Case 2 : If c2 + 4aα + 4as2 > 0. I Case 3 : If c2 + 4aα + 4as2 < 0. In this article, we only deal Case 1 and Case 2 For Case 1, that is c2 + 4aα + 4as2 = 0, the solution general of (26) is given by V (x, s) = (C1 (s)x + C2 (s))e c x − 2a 1 − a Z x c (x − τ )(f (τ, s) + ψ(τ ) + sϕ(τ ))e 2a τ dτ. 0 (27) M.Z. Djibibe, N. Pindra and K.Tcharie 9 Putting the intagral conditions (25) and (26) in (27), we get µ µ ¶¶ c ¢ c` −c` c ¡ 2 − 1 + e 2a C1 (s) + 1 − e− 2a C2 (s) 2a 2a Z `Z x c =2 (x − y)(f (τ, s) + ψ(τ ) + sϕ(τ ))e 2a τ dτ dx, 0 0 4a2 + (c2 `2 − 4ac` − 4a1 ))C1 (s) + (2a − (2a + `c))C2 (s) Z `Z x c 2 = 4a x(x − τ )(f (τ, s) + ψ(τ ) + sϕ(τ ))e 2a τ dτ dx. 0 0 For Case 1, that is c2 + 4aα + 4as2 > 0, Using the method of variation of parameter, to solve (26), we have the general solution as ! c2 + 4a(α + s2 ) x V (x, s) = C1 (s)exp − 2a à ! p c + c2 + 4a(α + s2 ) 2 + C2 (s)exp − x −p 2a c2 + 4a(α + s2 ) à ! p Z x 2 + 4a(α + s2 ) c(x−τ ) c × (f (τ, s) + ψ(τ ) + sϕ(τ )) e− 2a sinh (x − τ ) dτ, 2a 0 à c− p (28) where C1 et C2 are arbitrary functions of s. Substuting (28) into (25) and (26), we have ! p c2 + 4a(α + s2 ) x dx C1 (s) exp − 2a 0 à ! p Z ` c + c2 + 4a(α + s2 ) 2 + C2 (s) exp − x dx = p 2a c2 + 4a(α + s2 ) 0 à ! p Z `Z x 2 + 4a(α + s2 ) c(x−τ ) c × (f (τ, s) + ψ(τ ) + sϕ(τ )] e− 2a sinh (x − τ ) dτ dx, 2a 0 0 Z ` à c− (29) 10 Numerical solutions of integro-differential equation... ! p c2 + 4a(α + s2 ) C1 (s) x dx xexp − 2a 0 à ! p Z ` c + c2 + 4a(α + s2 ) 2 + C2 (s) xexp − x dx = p 2a c2 + 4a(α + s2 ) 0 à ! p Z `Z x 2 + 4a(α + s2 ) c(x−τ ) c × x (f (τ, s) + ψ(τ ) + sϕ(τ )] e− 2a sinh (x − τ ) dτ dx, 2a 0 0 Z ` à c− (30) where à ! à !−1 à ! C1 (s) a11 (s) a12 (s) b1 (s) = × , C2 (s) a21 (s) a22 (s) b2 (s) and ! p c2 + 4a(α + s2 ) a11 (s) = exp − x dx, (31) 2a 0 à ! p Z ` c + c2 + 4a(α + s2 ) a12 (s) = exp − x dx, (32) 2a 0 à ! p Z ` 2 2 c − c + 4a(α + s ) a21 (s) = xexp − x dx, (33) 2a 0 à ! p Z ` c + c2 + 4a(α + s2 ) a22 (s) = xexp − x dx, (34) 2a 0 Z `Z x c(x−τ ) a (f (τ, s) + ψ(τ ) + sϕ(τ )] e− 2a (35) b1 (s) = − p c2 + 4a(α + s2 ) 0 0 ! Ãp c2 + 4a(α + s2 ) (x − τ ) dτ dx, (36) × sinh 2a Z `Z x c(x−τ ) a b2 (s) = − p x (f (τ, s) + ψ(τ ) + sϕ(τ )] e− 2a c2 + 4a(α + s2 ) 0 0 (37) Ãp ! c2 + 4a(α + s2 ) × sinh (x − τ ) dτ dx. (38) 2a Z ` à c− If it is not possible to calculate the integral directly, then we calculate tem numerically. If the Laplace inversion is possibly computed directly for (28) and 11 M.Z. Djibibe, N. Pindra and K.Tcharie (38), we obtain our solution explicitly. Otherwise, we use the suitable approximate method, then we use the numerical inversion of the Laplace transform. We have ! c2 + 4a(α + s2 ) a11 (s) = x dx exp − 2a 0 à ! p n c − c2 + 4a(α + s2 ) 1X = ki exp − (xi + 1) , 2 i=1 2a Z ` à c− p ! p c2 + 4a(α + s2 ) a12 (s) = exp − x dx 2a 0 à ! p n c + c2 + 4a(α + s2 ) 1X = ki exp − (xi + 1) , 2 i=1 2a Z ` à ! p c2 + 4a(α + s2 ) a21 (s) = xexp − x dx 2a 0 à ! p n c − c2 + 4a(α + s2 ) 1X = ki (xi + 1)exp − (xi + 1) , 4 i=1 2a Z ` à c+ (39) ! c2 + 4a(α + s2 ) a22 (s) = xexp − x dx 2a 0 à ! p n c + c2 + 4a(α + s2 ) 1X = ki (xi + 1)exp − (xi + 1) , 4 i=1 2a Z ` à c− c+ p (40) b1 (s) = − p a Z `Z x (f (τ, s) + ψ(τ ) + sϕ(τ )] e− c2 + 4a(α + s2 ) 0 0 ! Ãp c2 + 4a(α + s2 ) (x − τ ) dτ dx × sinh 2a c(x−τ ) 2a 12 Numerical solutions of integro-differential equation... ¶ µ ¶ · µ 1 1 =− p ki f (xi + 1), s + ψ (xi + 1 2 2 4 c2 + 4a(α + s2 ) i=1 µ ¶ µ ·µ ¶ 1 c 1 + 1 − ( (xi + 1) exp − 1 − (xi + 1) xj 2 2a 2 Ãp µ ¶¸¶ X n c2 + 4a(α + s2 ) 1 sinh + 1 + (xi + 1) 2 2a j=1 · ·µ ¶ µ ¶¸ ¸¶ 1 1 1 1 × 1 − (xi + 1) xj + 1 + (xi + 1) − (xi + 1) 2 2 2 2 n X a a b2 (s) = − p Z `Z x x (f (τ, s) + ψ(τ ) + sϕ(τ )] e− c(x−τ ) 2a c2 + 4a(α + s2 ) 0 0 Ãp ! c2 + 4a(α + s2 ) × sinh (x − τ ) dτ dx 2a · µ ¶ µ ¶ 1 1 ki f b2 (s) = − p (xi + 1), s + ψ (xi + 1 2 2 4 c2 + 4a(α + s2 ) i=1 µ ¶¸ µ ¶ µ ·µ ¶ 1 1 1 1 +sϕ (xi + 1 1 − ( (xi + 1) 1 − (xi + 1) xj 2 2 2 2 ¶¸¶ µ ·µ ¶ µ c 1 1 exp − 1 − (xi + 1) xj + 1 + (xi + 1) 2 2a 2 Ãp µ ¶¸¶ X n c2 + 4a(α + s2 ) 1 + 1 + (xi + 1) sinh 2 2a j=1 · ·µ ¶ µ ¶¸ ¸¶ 1 1 1 1 × 1 − (xi + 1) xj + 1 + (xi + 1) − (xi + 1) . 2 2 2 2 a n X where xi and ki are the abscissa and weights, defined as xi : ith zero of Pn (x), ki = 2 (1 − x2i )(P 0 (x))2 Their tabulated values can be found in [7] for different values of N. Using Stehfest’s algorithm, the time domain solution is approximated as µ ¶ min(k,n) 2n X ln 2 X k ln 2 in (2i)!(−1)k+n v(x, t) ' V x, . t k=1 2 t 3 (n − i)!i!(i − 1)!(k − i)!(2i − k)! k+1 5 i=4 2 (41) M.Z. Djibibe, N. Pindra and K.Tcharie 13 References [1] A. Merad, On solvability of the integrodifferential hyperbolic equation with purely nonlocal conditions, Science Direct, Acta Mathematica Science. [2] A. Merad and al., Existence and Uniqueness for a Solution of pseudohyperbolic equation with Nonlocal Boundary Condition, Applied Mathematics & Information Science, 9(2), (2015), 1-7. [3] A. Merad and al., Numerical Solutions of the hyperbolic equation with purely integral condition by using Laplace Transform method, Palestine Journal of Mathematics, 4(1), (2015), 30-36. [4] L. Bougoffa, Parabolic equations with nonlocal conditions, Applied Mathematical Science, 1(21), (2007), 1041-1048. [5] J.R. Cannon, The solution of heat equation to the specification of energy, Quart. Appl. 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